Oithona nana - Tropical Cyclopoid Copepod for Warm-Water Marine Aquaculture

Scientific Classification & Taxonomy

Kingdom: Animalia | Phylum: Arthropoda | Subphylum: Crustacea | Class: Maxillopoda | Subclass: Copepoda | Order: Cyclopoida | Family: Oithonidae | Genus: Oithona | Species: O. nana

Complete Oithona nana Species Profile for Marine Aquaculture

Oithona nana ranks among the most geographically widespread and numerically abundant copepod species in tropical and subtropical oceans worldwide, occurring throughout the Indo-Pacific, Atlantic, and Caribbean regions between approximately 40°N and 40°S latitude. This small warm-water cyclopoid copepod dominates zooplankton communities in oligotrophic (nutrient-poor) tropical waters where its energy-efficient ambush-feeding strategy provides competitive advantages over larger, more active copepod species. For aquaculture operations culturing tropical marine fish—groupers, snappers, sea bass, sea bream, pompano, cobia, mahimahi, barramundi, and coral reef ornamentals—O. nana represents an ultra-small live feed option perfectly adapted to warm-water conditions and capable of bridging critical size gaps during early larval development.

Adult Oithona nana measure 0.6-0.9 millimeters in body length, making this one of the smallest commonly occurring copepod species in marine plankton. Females (0.7-0.9mm) slightly larger than males (0.6-0.8mm). This extremely small adult size positions O. nana as the smallest practical live feed option for marine larviculture, with nauplii measuring only 60-80 micrometers—smaller than many rotifer strains and approaching the theoretical minimum prey size for visual-feeding fish larvae.

Body coloration typically transparent to very pale cream with subtle internal organs visible through the translucent cuticle. Well-fed individuals may show faint orange or brown tint from accumulated carotenoid pigments. The near-transparent appearance makes O. nana virtually invisible in aquarium water, but characteristic jerky swimming behavior—brief pause, rapid burst, pause—creates hydrodynamic disturbances triggering predation responses in fish larvae adapted to detect movement rather than color contrast. Body structure shows typical cyclopoid characteristics: compact, nearly spherical cephalothorax, short abdomen with paired caudal rami (tail appendages), and relatively short first antennae compared to the elongated antennae of calanoid copepods like Acartia or Pseudodiaptomus.

Tropical Specialization and Ambush-Feeding Ecology

Oithona nana exhibits remarkable adaptations to warm, often nutrient-limited tropical waters where many larger copepod species struggle to maintain populations. These adaptations center on an energy-efficient lifestyle minimizing metabolic expenditure while maximizing prey capture efficiency in environments where food resources are sparse and competition intense.

Like all Oithona species, O. nana practices highly specialized "ambush predation" rather than active suspension feeding. The copepod remains nearly motionless in the water column—suspended by occasional subtle antenna movements—while sensitive mechanoreceptors detect hydrodynamic disturbances from approaching prey organisms at distances up to 2-3 body lengths. Upon detecting suitable prey (swimming bacteria, flagellates, ciliates, small phytoplankton cells, organic particles), O. nana strikes with explosive acceleration, capturing prey items in approximately 10-15 milliseconds through rapid extension of specialized feeding appendages.

This sit-and-wait strategy dramatically reduces energy expenditure compared to continuously swimming copepods that create feeding currents. Research suggests O. nana expends 50-70% less energy than similarly sized calanoid copepods, allowing viable populations to persist in oligotrophic tropical waters where food concentrations would starve actively feeding species. The ambush strategy also allows O. nana to exploit prey items other copepods miss—motile microzooplankton (heterotrophic dinoflagellates, ciliates) and bacterial aggregates swimming through the water column rather than suspended phytoplankton cells that suspension feeders capture more efficiently.

In tropical reef environments and open ocean gyres, O. nana plays a critical ecological role connecting microbial food webs (bacteria, nanoflagellates, small phytoplankton) to higher trophic levels (larval fish, small planktivorous fish, larger zooplankton). This "microbial loop" pathway proves essential in tropical waters where most primary production occurs at the bacterial and picoplankton scale (<2 micrometers) rather than the larger phytoplankton cells (>10 micrometers) dominating temperate productive waters.

Environmental Requirements and Tolerance

Salinity: Highly euryhaline with broad tolerance 18-42 ppt, optimal reproduction at 30-36 ppt. Natural populations primarily occur at full marine salinity (33-36 ppt) in open ocean environments, though coastal populations tolerate brackish conditions near river outflows, particularly during rainy seasons in tropical regions. Culture at standard marine salinity 32-35 ppt for optimal reproduction and ease of management, or reduce to 25-30 ppt if cost optimization important (reducing salt consumption 15-30%) without significantly impacting health or reproduction.

Temperature: Tropical/subtropical specialist with warm-water requirements:

• Optimal range: 24-28°C (75-82°F) for maximum reproduction and growth
• Acceptable range: 20-30°C (68-86°F) maintains healthy populations
• Lower tolerance: 18-20°C (64-68°F) causes reduced activity, slower reproduction, increased mortality risk
• Upper tolerance: 30-32°C (86-90°F) tolerated short-term but stressful long-term
• Critical limits: <16°C (<61°F) or >33°C (>91°F) causes rapid mortality

Thermal Preference Implications: O. nana matches temperature requirements of tropical groupers, snappers, cobia, pompano, barramundi, and coral reef ornamentals. Facilities maintaining 25-28°C larval rearing systems can culture O. nana at identical temperatures, eliminating temperature management conflicts. However, O. nana unsuitable for temperate species (sea bass, sea bream, halibut) cultured at 15-20°C—use O. similis or Acartia for cold-water applications.

Water Quality Requirements:

• Ammonia/Nitrite: Must be 0 ppm—highly sensitive to nitrogenous toxins
• Nitrate: <20 mg/L preferred, <50 mg/L maximum
• Dissolved Oxygen: >6 mg/L required, >7 mg/L optimal (warm water holds less oxygen than cold)
• pH: 8.0-8.3 optimal, maintain stability avoiding rapid fluctuations (>0.2 units/day)

Small body size, high surface-area-to-volume ratio, and elevated metabolic rate at warm temperatures require excellent water quality. Adequate aeration absolutely essential—warm water (25-28°C) naturally holds 20-30% less dissolved oxygen than cold water (5-10°C), necessitating vigorous aeration to maintain >6 mg/L. However, avoid excessive turbulence disrupting ambush-feeding behavior. Goal: gentle circulation maintaining high oxygen while preserving calm micro-zones where O. nana can remain motionless for prey detection.

Life Cycle and Reproduction

Egg Stage: Females carry eggs in paired egg sacs attached to genital segment (urosome), characteristic of all cyclopoid copepods. Each egg sac contains 8-18 eggs depending on female size, nutritional status, and temperature. Smaller clutches than larger Oithona species (O. similis, O. plumifera) but higher reproductive turnover compensates. Females provide parental care by carrying eggs until hatching, protecting from predation and maintaining optimal oxygen conditions. Development strongly temperature-dependent: 20°C (4-5 days), 24°C (2.5-3.5 days), 28°C (1.5-2.5 days), 30°C (1-2 days). Eggs measure 45-60 micrometers diameter—among smallest of cultured copepods.

Naupliar Stages: Six stages (N1-N6) showing progressive development. Nauplii hatch at 60-80 micrometers, providing the smallest practical live feeds available for marine larviculture—smaller than most rotifer strains (Brachionus plicatilis S-type 100-150μm, L-type 150-210μm) and approaching the theoretical minimum prey size for visual-feeding fish larvae (approximately 50-60μm). Development: 20°C (12-18 days), 24°C (8-12 days), 28°C (6-9 days), 30°C (5-7 days).

Early nauplii (N1-N3) feed primarily on bacteria, bacterial aggregates (flocs), ultra-small phytoplankton (<3 micrometers including picoplankton), and organic detritus. This feeding flexibility proves advantageous for culture—O. nana nauplii less dependent on high phytoplankton concentrations than calanoid nauplii (Acartia, Pseudodiaptomus) which require abundant phytoplankton for successful development. Later nauplii (N4-N6) increasingly consume larger phytoplankton (3-8 micrometers) and begin predating on small ciliates and heterotrophic flagellates.

Nauplii show moderate positive phototaxis (attraction to light), facilitating visual detection by fish larvae. Swimming behavior alternates between brief swimming bursts and passive sinking/suspension, creating movement patterns triggering predatory strikes from larvae.

Copepodid Stages: Five stages (C1-C5) with progressive size increase and morphological differentiation toward adult form. Development: 20°C (18-26 days), 24°C (12-18 days), 28°C (9-14 days), 30°C (7-11 days). Size progression: C1 (120 micrometers) → C2 (180 micrometers) → C3 (280 micrometers) → C4 (420 micrometers) → C5 (580 micrometers), perfectly scaling with growth of tropical fish larvae from 2.5-3mm at first feeding to 6-9mm at metamorphosis.

Feeding shifts increasingly toward microzooplankton predation: ciliates (Euplotes, Strombidium, Tintinnids), heterotrophic dinoflagellates (Oxyrrhis, Gyrodinium), nauplii of other copepods, and small rotifers. Phytoplankton remains supplemental food source. Ambush-feeding behavior becomes fully developed by C3 stage.

Adult Stage: Sexual maturity reached after final molt from C5 to adult: 20°C (35-50 days from hatching), 24°C (25-38 days), 28°C (20-30 days), 30°C (16-24 days). Faster maturation than cold-water O. similis (60-90 days at 2-8°C) but slower than warm-water harpacticoids like Tisbe biminiensis (12-18 days at 25°C) or tropical calanoids like Parvocalanus (14-20 days at 25-28°C).

Females produce first egg sac 3-7 days after reaching maturity, then release subsequent broods every 4-8 days depending on temperature and food availability. Warmer temperatures within optimal range (27-28°C) accelerate brood production; cooler temperatures (22-24°C) extend inter-brood intervals but may increase egg viability.

Lifespan: 20°C (3-5 months), 24°C (2-4 months), 28°C (1.5-3 months), 30°C (1-2.5 months). Lifetime fecundity 120-400 offspring per female depending on temperature regime and nutritional conditions. Lower total fecundity than larger Oithona species, but faster generation time in warm water allows rapid population growth once established.

Population doubling time: 20°C (25-40 days), 24°C (18-28 days), 28°C (14-22 days), 30°C (12-18 days). Moderate reproduction rate—slower than Acartia tonsa (10-18 days at 18-22°C), Apocyclops panamensis (8-14 days at 25-28°C), or harpacticoids (10-16 days), but adequate for sustained production with proper management.

Nutritional Composition and Ultra-Small Larval Feed Value

Protein: 38-48% dry weight with complete essential amino acid profile suitable for early larval nutrition. Protein content varies with diet—well-fed copepods on mixed phytoplankton show 45-48%, while copepods on bacteria-dominated diets show 38-42%.

Essential Fatty Acids - EPA and DHA:

O. nana fatty acid composition highly flexible, reflecting diverse natural diet (bacteria, phytoplankton, microzooplankton):

• EPA (Eicosapentaenoic Acid, 20:5n-3): 10-28% of total fatty acids depending on phytoplankton diet
• DHA (Docosahexaenoic Acid, 22:6n-3): 6-20% of total fatty acids depending on phytoplankton diet
• Total Omega-3 PUFA: 28-50% of total fatty acids with appropriate enrichment
• Lower baseline EPA+DHA than larger Oithona species or calanoids, but enrichable through targeted feeding

Enrichment Strategy for Maximum EPA+DHA:

For EPA maximization:

• Nannochloropsis oculata (25-40% EPA of total fatty acids): Primary phytoplankton base
• Chaetoceros calcitrans (20-35% EPA): Excellent supplement providing chain-forming diatom structure
• Phaeodactylum tricornutum (20-30% EPA): Alternative diatom option

For DHA maximization:

• Tisochrysis lutea (12-18% DHA, formerly Isochrysis galbana T-ISO): Industry standard DHA source
• Pavlova lutheri (18-25% DHA plus 20-30% EPA): Exceptional balanced profile but more demanding to culture
• Rhodomonas salina (8-15% DHA): Additional DHA source plus high protein

Optimal balanced diet for O. nana enrichment: 60-65% Nannochloropsis (EPA foundation), 25-30% Tisochrysis or Pavlova (DHA source), 10-15% Rhodomonas (additional DHA, protein, vitamins, pigments). Maintain light to medium green water coloration (400,000-900,000 cells/ml total concentration) providing continuous feeding opportunities without excessive organic loading.

Feed phytoplankton continuously rather than batch additions—O. nana feeds throughout 24-hour cycle via ambush strikes on swimming phytoplankton cells. Continuous low-level feeding (via drip system or multiple daily additions) maintains gut fullness and maximizes fatty acid accumulation.

Micronutrient and Digestibility Value:

• High digestibility: 80-90% absorption efficiency despite very small size
• Carotenoid accumulation: Astaxanthin, canthaxanthin, lutein from phytoplankton diet support larval vision development and pigmentation
• Vitamin E and C: Antioxidants supporting larval immune function and stress resistance
• Natural chitinase inhibitors: Support larval digestive enzyme development
• Bacterial associations: Body surface microbiome may provide probiotic benefits to larvae

Critical Advantage - Ultra-Small First Feeds:

O. nana provides smallest practical copepod prey for marine fish larvae:

• Nauplii 60-80μm vs rotifer S-type 100-150μm vs Artemia nauplii 400-500μm
• Bridges critical size gap for species with very small first-feeding larvae (<2.5mm total length)
• Examples: Certain grouper species, small snapper species, butterfly fish, angelfish, anthias
• Larvae with mouth gapes <100μm can successfully capture O. nana nauplii but struggle with larger rotifers

Specialized Marine Fish Hatchery Applications

Ultra-Small Larvae - Critical First-Feeding Applications:

Groupers (Epinephelus spp., Mycteroperca spp.):

• Many grouper species hatch at 1.8-2.2mm total length with mouth gape 60-90μm
• First 5-7 days post-hatch critically sensitive to prey size
• O. nana nauplii (60-80μm) provide ideal first feeds before transitioning to rotifers or larger copepods
• Species benefiting: Coral trout (E. coralicola), Hong Kong grouper (E. akaara), Red grouper (E. morio), Nassau grouper (E. striatus)

Snappers (Lutjanus spp.):

• Larvae hatch at 1.5-2.5mm depending on species
• Small mouth gapes (70-100μm) during first week
• O. nana bridges rotifer-to-larger-copepod transition
• Species benefiting: Mangrove snapper (L. argentimaculatus), Yellowtail snapper (L. chrysurus), Lane snapper (L. synagris)

Coral Reef Ornamentals - High-Value Species:

Angelfish (Pomacanthidae):

• Tiny larvae (1.5-2.0mm) with extended pelagic larval duration (20-40+ days)
• O. nana provides continuous appropriate-sized prey throughout larval development
• Commercial breeding potential: Emperor angelfish, Queen angelfish, French angelfish, Flame angelfish

Butterfly fish (Chaetodontidae):

• Very small larvae requiring ultra-fine prey
• Extended planktonic phase (30-50 days) before settlement
• O. nana maintains size-appropriate feeding throughout development

Anthias (Serranidae subfamily Anthiinae):

• Small larvae (1.8-2.5mm) from these popular reef fish
• O. nana ideal for commercial breeding programs
• Species potential: Lyretail anthias, Bartlett's anthias, Sunburst anthias

Extended Larval Development Species:

Tropical fish with prolonged larval periods (40-90 days) benefit from continuous O. nana supplementation:

• Surgeonfish/tangs (Acanthuridae): Yellow tang, Blue tang, Powder blue tang
• Wrasses (Labridae): Fairy wrasses, Flasher wrasses
• Damselfish (Pomacentridae): Beyond typical clownfish—rare chromis, dascyllus species

Research and Development Applications:

• Larval fish feeding behavior studies using size-graded prey
• Nutritional studies comparing copepod families (Cyclopoida vs Calanoida vs Harpacticoida)
• Prey size selection experiments determining optimal size ranges for different species
• Microbiome research investigating copepod-larva microbial transfer
• First-feeding protocols for newly cultured ornamental species

Current Commercial Limitations:

O. nana not yet widely adopted in commercial hatcheries due to:

• Slower reproduction than Acartia, Parvocalanus, or Apocyclops
• Smaller harvest volumes per liter requiring larger culture infrastructure
• Less established culture protocols compared to industry-standard species
• Higher technical expertise requirements

Primary current use: Research facilities, specialized ornamental fish breeding programs, operations targeting ultra-small-larvae species where O. nana provides unique advantages justifying additional complexity.

Reef Aquarium Applications

Small-Polyp Scleractinian (SPS) Coral Nutrition:

O. nana represents ideal size match for SPS corals with tiny polyps (<3mm):

Acropora species (staghorn, tabletop, branching): Polyps 1-3mm benefit from 60-400μm prey (O. nana nauplii through small copepodids). Regular feeding improves growth rates 30-60%, enhances polyp extension, intensifies coloration through carotenoid pigment accumulation.

Montipora species (plating, encrusting, branching): Polyps 1-2mm perfectly matched to O. nana size range. Feeding supports tissue growth over skeleton, improves coloration (purple, green, orange pigments), increases resistance to bleaching stress.

Pocillopora, Seriatopora, Stylophora: Small-polyp species responding well to zooplankton feeding. O. nana provides authentic planktonic prey triggering natural feeding responses.

Feeding Protocol for SPS Corals:

• Turn off circulation pumps 15-30 minutes
• Add O. nana culture (nauplii through adults) at 500-2000 copepods per 10 gallons
• Observe polyp extension and feeding behavior
• Resume circulation after 20-40 minutes
• Feed 2-4x weekly for best results

Filter-Feeding Invertebrates:

Basket stars (Gorgonocephalidae): Nocturnal suspension feeders capturing copepods with branching arms. O. nana size perfect for arm mesh capture.

Feather stars - Crinoids (Comatulidae): Filter plankton using feathery arms. O. nana swimming behavior triggers capture reflexes.

Feather duster worms (Sabellidae): Radioles (feeding tentacles) efficiently capture copepods 50-500μm. O. nana provides complete size range.

Christmas tree worms (Serpulidae): Small spiral feeding crowns capture fine zooplankton. O. nana nauplii and copepodids ideal size.

Sponges (Porifera): Some aquarium sponges (especially photosynthetic species with symbiotic zooxanthellae) supplement photosynthesis with filter feeding. O. nana plus bacteria provide nutrition supporting sponge health.

Planktivorous Nano Fish - Ultra-Small Species:

Dwarf gobies (Eviota spp., Trimma spp.): Among smallest marine fish (15-25mm adult). Tiny mouths suited to small copepods. O. nana perfect for acclimation, conditioning, maintaining health in captivity.

Small dartfish (Ptereleotris spp.): Juvenile and small adult dartfish benefit from O. nana during acclimation to aquarium life before transitioning to prepared foods.

Nano anthias: Small anthias species in nano reef aquariums (10-30 gallons) benefit from O. nana preventing overfeeding and bioload issues caused by larger copepods.

Important Feeding Considerations:

Visibility Limitation: O. nana transparent appearance provides minimal visual contrast. Not ideal primary food for species requiring high-contrast prey:

• Mandarins (Synchiropus spp.): Better served by orange Tigriopus californicus
• Seahorses/pipefish: Need larger, more visible prey (Tisbe, Tigriopus, Apocyclops)
• Most wrasses, dottybacks, aggressive feeders: Prefer larger, more visible copepods

Best Used as Supplement: Combine O. nana with more visible copepod species:

• 60-70% Tigriopus californicus (orange, large, benthic)
• 20-30% Tisbe biminiensis or Apocyclops panamensis (medium size, active)
• 10-20% O. nana (ultra-small, planktonic diversity)

This mixed approach provides complete size range (60μm to 1400μm), habitat diversity (benthic and planktonic), and high visibility from Tigriopus combined with specialized ultra-small prey from O. nana.

Refugium Biodiversity Enhancement:

Establishing O. nana populations in refugiums increases zooplankton diversity creating authentic planktonic communities mimicking natural reef environments. Benefits:

• Size-stratified prey availability (different life stages 60-900μm)
• Temporal diversity (24-hour availability vs pulsed feeding)
• Ecological complexity supporting coral, invertebrate, and fish health
• Educational value observing natural zooplankton behavior

Culture Requirements and Methods

Culture Setup - Tropical Temperature Systems:

Small-scale (20-100L): Clear cylindrical containers allowing observation, submersible aquarium heaters (50-200W) maintaining 25-28°C, gentle aeration via fine-bubble air stones, 12-16 hour photoperiod with low-moderate intensity lighting (50-150 μmol photons/m²/s), ambient room temperature 22-26°C reducing heater workload.

Medium-scale (100-500L): Multiple culture vessels for staggered production, centralized heating system (heated room or heated water bath) maintaining stable 26-28°C, filtered seawater supply (1-5 micrometer cartridge filtration), separate vessels for life stages (nauplii/copepodids/adults allow stage-specific optimization), climate-controlled room ideal but not essential if ambient temperature stable.

Large-scale (500-5000+L): Dedicated culture facility with temperature control (heated room 26-28°C most economical for large volumes), continuous phytoplankton culture systems (3-5x copepod culture volume), automated temperature and dissolved oxygen monitoring with alarms, multiple production lines for redundancy and staggered harvests, egg collection systems (less critical than for broadcast spawning species like Acartia), supplemental microzooplankton cultures enhancing nutrition.

Container Design Principles:

• Minimum depth: 40cm (deeper preferable for larger volumes: 60-100cm)
• Shape: Cylindrical or conical vessels with rounded bottoms (no sharp corners where debris accumulates)
• Color: Light-colored or translucent walls aid monitoring (dark bottoms less critical than for Acartia)
• Surface area: Adequate for gas exchange (surface area:volume ratio minimum 1:4, 1:3 better)
• Overflow: Fine mesh (100-120μm) preventing copepod escapement during water exchange
• Coverage: Loose lids or mesh covers preventing contamination while allowing air exchange

Aeration Strategy - Critical for Warm Water:

Warm water (25-28°C) holds 20-30% less dissolved oxygen than cold water (5-10°C), making vigorous aeration essential. However, excessive turbulence disrupts ambush-feeding behavior. Solution: balanced approach.

Recommended aeration setup:

• Fine-bubble air stones positioned near bottom
• Moderate air flow creating gentle vertical circulation
• Rising bubble column lifts water slowly without violent turbulence
• Target: dissolved oxygen >7 mg/L, gentle water movement allowing O. nana to remain suspended for ambush feeding
• Avoid: vigorous splashing, strong horizontal currents, excessive turbulence

Monitor dissolved oxygen daily in warm-water cultures—warm temperatures + high metabolic activity + small copepod size = rapid oxygen depletion if aeration fails.

Lighting:

Low to moderate intensity: 50-150 μmol photons/m²/s, 12-16 hour photoperiod. Primarily supports phytoplankton growth rather than copepod physiology. Excessive lighting unnecessary and promotes nuisance phytoplankton blooms. Many facilities use ambient room lighting (fluorescent ceiling lights on 12-14 hour timer), supplementing with aquarium lights positioned near cultures if needed.

Feeding Strategy - Multi-Trophic Approach

O. nana's diverse natural diet (bacteria, phytoplankton, microzooplankton) suggests multi-trophic feeding approach yields best results:

Primary Phytoplankton Foundation (60-70% of feeding effort):

Nannochloropsis oculata (2-4μm):

• Excellent EPA source (25-40%)
• Small size perfect for all O. nana life stages
• Hardy, reliable cultures tolerating 20-30°C
• Primary phytoplankton base—culture at 3-5x copepod volume

Tisochrysis lutea / Isochrysis galbana (4-6μm):

• Excellent DHA source (12-18%)
• Moderate EPA (8-15%)
• Cultured at 20-26°C
• 20-30% of phytoplankton mix

Rhodomonas salina (6-10μm):

• Good DHA (8-15%)
• Excellent protein content
• Rich vitamins and carotenoids
• 10-15% of phytoplankton mix

Phytoplankton Feeding Protocol:

Maintain light to medium green water: 500,000-1,000,000 cells/ml total phytoplankton concentration. Higher concentrations than typical for Acartia or harpacticoid cultures because:

1. O. nana feeds continuously via ambush strikes requiring constant prey availability
2. Small body size means frequent feeding essential (high surface-area-to-volume ratio)
3. Some phytoplankton consumed by bacterial populations supporting nauplii

Daily feeding schedule:

• Morning (8-9am): Add 30-35% of daily phytoplankton ration
• Midday (12-1pm): Add 15-20% if monitoring shows color fading
• Evening (6-7pm): Add remaining 45-50% of daily ration
• Total daily: Sufficient volume maintaining green color (typically 10-25% of culture volume as concentrated phytoplankton depending on culture density)

Supplemental Microzooplankton (20-30% of feeding effort):

Ciliates (Euplotes, Paramecium):

• Culture separately in small containers (5-20L) at 24-28°C
• Feed ciliates with bacteria cultures or commercial ciliate food
• Add to O. nana cultures: 2,000-5,000 ciliates/ml twice weekly
• Excellent nutrition for copepodids and adults
• Challenging to maintain but significantly improve growth rates

Small rotifers (Brachionus plicatilis):

• Small amounts (100-300 rotifers/ml) once or twice weekly
• Supplemental prey for larger copepodids and adults
• Also consume nuisance bacteria and detritus (beneficial side effect)

Heterotrophic dinoflagellates:

• May establish naturally in mature cultures if organic loading allows
• Do NOT deliberately add unless experienced with dinoflagellate culture
• Can bloom excessively causing water quality problems if uncontrolled

Bacterial Enhancement (10-20% of feeding effort):

Probiotic bacteria additions:

• Small amounts support naupliar nutrition (N1-N3 feed heavily on bacteria)
• Options: Commercial aquaculture probiotics (Bacillus spp.), baker's yeast (Saccharomyces cerevisiae)
• Dosage: 0.05-0.15 g baker's yeast per 100L daily, dissolved in seawater before adding
• Critical: avoid overfeeding—excess organics degrade water quality rapidly in warm water

Benefits: Bacterial aggregates (flocs) provide ultra-small nauplii with abundant food, supporting survival and growth during critical early stages.

Water Management - Maintaining Quality in Warm Systems

Batch Culture Method (Most Common for Small-Medium Operations):

Perform 25-40% water changes 2-3 times weekly (Monday-Wednesday-Friday or Tuesday-Thursday-Saturday):

1. Stop aeration 5-10 minutes before water change
2. Allow copepods to distribute throughout water column or settle slightly
3. Gently siphon water from mid-depth using large-bore tubing (avoid disturbing bottom sediments containing eggs/nauplii)
4. Pass siphoned water through 100-120μm mesh collecting any copepods, rinse collected copepods back into culture
5. Prepare replacement seawater: filter to 1-5 micrometers, adjust temperature to exact culture temperature (±0.5°C maximum difference), adjust salinity matching culture (±1 ppt)
6. Slowly add replacement water over 15-30 minutes avoiding temperature shock or osmotic stress
7. Resume aeration
8. Feed phytoplankton immediately after water change

Critical in warm water: Bacterial metabolism and organic decomposition accelerate dramatically at 25-28°C compared to cold water. Regular water changes essential removing accumulated metabolites, preventing ammonia/nitrite buildup, and maintaining stable pH.

Semi-Continuous Flow (Better for Large-Scale Operations):

5-20% daily water exchange through fine mesh overflow:

• Surface overflow with 100-120μm mesh retaining all copepod life stages
• Drip or slow-flow replacement of filtered, temperature-matched seawater
• Maintains stable water parameters
• Reduces labor compared to manual batch water changes
• Requires reliable temperature control on incoming water (inline heaters or pre-heated reservoir)

Flow-Through (Advanced/High-Density Systems):

Continuous low-flow: 0.5-2 system volumes exchanged daily

• Incoming water through fine mesh (100-120μm) retaining copepods
• Requires abundant phytoplankton supply continuously added
• Highest water quality stability
• Most expensive (heating costs for continuous seawater flow)
• Best for very high-density cultures (>800 copepods/L) or sensitive larvae feeding protocols

Water Quality Monitoring Schedule:

• Temperature: 2-3x daily minimum (morning, afternoon, evening) + continuous data loggers with high/low alarms ideal
• Salinity: Every 3-4 days (±2 ppt acceptable, adjust with RO water or marine salt)
• pH: 2-3 times weekly (8.0-8.3 range, adjust with sodium bicarbonate if declining below 7.8)
• Dissolved Oxygen: Daily in dense cultures (>400 copepods/L), 2-3x weekly in lower density, MUST maintain >6 mg/L minimum, >7 mg/L preferred
• Ammonia: Weekly (must be 0 ppm using Nessler reagent or salicylate method)
• Nitrite: Weekly (must be 0 ppm)
• Nitrate: Weekly (<20 mg/L ideal, <50 mg/L maximum)
• Phytoplankton density: Daily visual assessment (light-medium green), weekly cell counts via microscope or fluorometer if available
• Copepod density: Weekly enumeration via microscope counts of 5-10ml samples (minimum 3 samples per culture for statistical reliability)

Critical Parameter - Dissolved Oxygen in Warm Water:

Warm water holds less oxygen: 8.3 mg/L at 25°C vs 11.3 mg/L at 5°C (30% reduction). Combined with elevated copepod metabolic rate and faster bacterial decomposition, warm-water cultures face continuous oxygen challenges. Install backup aeration systems (battery-powered air pumps, oxygen cylinders) for power outages—copepod mortality begins within 2-4 hours if aeration stops at 25-28°C.

Harvesting Methods and Production Yields

Harvesting Techniques:

Fine mesh collection (120-150μm):

• Most common method for concentrated harvests
• Gently sweep aquarium net through mid-water column
• Avoid disturbing bottom sediments (contain eggs and early nauplii)
• Transfer collected copepods to clean seawater bucket for rinsing before use
• Multiple gentle sweeps concentrate copepods without causing injury

Siphon concentration:

• Use large-bore flexible tubing (1-2cm internal diameter)
• Siphon culture water through fine mesh (120-150μm) collection bucket
• Copepods retained on mesh, culture water flows through
• Very gentle method suitable for delicate nauplii
• Rinse collected copepods with clean seawater at same temperature before transfer

Light attraction (passive harvest - moderate effectiveness):

• O. nana shows moderate positive phototaxis (less than Acartia, more than benthic harpacticoids)
• Place light source on one side of culture 1-2 hours before harvest
• Copepods concentrate near light (especially nauplii and young copepodids)
• Facilitates collection by concentrating population
• Best results at night when contrast between light and surrounding darkness maximized

Surface overflow collection (continuous low-level harvest):

• During water exchanges, slightly increase overflow rate
• Fine mesh on overflow (100-120μm) catches copepods
• Passive collection while performing water maintenance
• Lower stress than active netting
• Yields smaller quantities but consistent and gentle

Recommended Harvest Schedule:

Conservative sustainable harvest: 10-20% of population weekly Standard production harvest: 20-30% of population weekly Intensive harvest: 30-40% of population weekly (requires excellent feeding, water quality, supplemental microzooplankton)

Never exceed 45% harvest in single event—risks population crash and extended recovery period. For continuous daily harvests, limit to 2-5% daily (14-35% weekly total).

Production Yields at Different Management Intensities:

Low-intensity management:

• Minimal intervention: phytoplankton 2-3x weekly, water changes 1-2x weekly
• Standing density: 30-120 copepods/L
• Harvest: 5-20 copepods/L weekly

Medium-intensity management:

• Regular care: daily phytoplankton feeding, 2-3x weekly water changes, weekly monitoring
• Standing density: 120-500 copepods/L
• Harvest: 20-100 copepods/L weekly

High-intensity management:

• Intensive protocols: multiple daily phytoplankton feedings, microzooplankton supplementation, 3-4x weekly water changes, daily monitoring, separate life-stage cultures
• Standing density: 500-1200 copepods/L
• Harvest: 100-350 copepods/L weekly

Commercial-scale targets for specialized operations:

• Maintain standing density: 300-700 copepods/L
• Daily harvest: 40-140 copepods/L
• Weekly total harvest: 280-980 copepods/L

Important Notes on Yields:

1. O. nana yields typically 30-50% lower than Acartia tonsa, Parvocalanus crassirostris, or Apocyclops panamensis at equivalent temperatures due to slower reproduction
2. However, ultra-small size means more copepods needed per liter of fish tank (5,000-10,000 O. nana nauplii vs 2,000-5,000 Acartia nauplii for same fish larvae density)
3. Must scale culture volumes 2-3x larger than for Acartia or Parvocalanus to achieve equivalent larval feeding capacity
4. Justified for specialized applications where ultra-small prey size provides unique advantages

Culture Challenges and Practical Solutions

Challenge: Slower Reproduction Limiting Production Volumes

Problem: Generation time 20-30 days at 25-28°C (vs 10-18 days for Acartia or Parvocalanus), smaller clutch sizes (8-18 eggs vs 20-40 for larger species)

Solutions:

• Maintain larger culture volumes compensating for lower per-liter yields (if target is 50,000 copepods/day harvest, plan for 150-250L culture vs 50-100L for faster-reproducing species)
• Use multiple staggered cultures providing continuous harvests despite slower reproduction
• Plan production 2-3 months in advance of fish spawning seasons
• Optimize nutrition with mixed phytoplankton diets including microzooplankton supplements
• Maintain optimal temperature (27-28°C) within species tolerance for fastest reproduction
• Never overharvest—stay below 30% weekly to maintain population stability

Challenge: Very Small Size Complicates Harvesting and Handling

Problem: Nauplii 60-80μm and adults only 600-900μm difficult to see, collect efficiently, and enumerate accurately

Solutions:

• Use fine mesh nets (120-150μm) rather than standard zooplankton nets (200-300μm) which allow small individuals to escape
• Implement gentle harvesting methods minimizing stress and physical damage
• Use light attraction to concentrate copepods before collection
• Employ passive collection via surface overflow during routine water changes (less stressful than active netting)
• For enumeration, use graduated cylinders or volumetric approach rather than counting individuals (sample 1ml, count under dissecting microscope, multiply by total volume)
• Consider using flow cytometry or automated particle counters for large-scale operations needing precise counts

Challenge: Nearly Invisible in Aquariums - Poor Visual Feedback

Problem: Transparent body provides minimal visual contrast in reef aquariums, difficult for aquarists to observe feeding success or population establishment

Solutions:

• Not a problem for larval fish culture (larvae detect movement, not color)
• For reef aquariums: combine O. nana with visible copepod species (60-70% Tigriopus californicus orange, 20-30% Apocyclops or Tisbe, 10-20% O. nana)
• Examine coral polyp extension and feeding behavior rather than trying to observe copepods directly
• Use microscope to verify population in refugiums (sample small amount, examine under 40-100x magnification)
• Focus on applications where ultra-small size provides unique value justifying invisibility trade-off

Challenge: Multi-Trophic Feeding Requirements

Problem: Best results require phytoplankton + microzooplankton + bacteria rather than simple phytoplankton-only protocols successful for Acartia or Parvocalanus

Solutions:

• Start with phytoplankton-only cultures to establish basic population, then progressively add complexity (microzooplankton, bacteria) as experience grows
• Maintain separate ciliate cultures in small containers (5-20L) requiring minimal space/effort, add to copepod cultures 2x weekly
• Use small amounts of rotifers as easy supplemental microzooplankton (most facilities already culturing rotifers for larviculture)
• Add probiotic bacteria cautiously in small amounts—benefits nauplii without excessive organic loading
• Accept moderate yields initially, optimize gradually as husbandry skills improve

Challenge: Water Quality Deterioration in Warm Water

Problem: Accelerated bacterial metabolism, faster organic decomposition, lower oxygen solubility, higher copepod metabolic rate all stress water quality at 25-28°C

Solutions:

• Implement more frequent water changes than cold-water cultures (3x weekly minimum vs 2x weekly for cold cultures)
• Install robust aeration systems with backup power for outages
• Monitor dissolved oxygen daily rather than 2-3x weekly
• Use larger surface-area-to-volume ratio culture vessels (shallower, wider rather than deep, narrow)
• Avoid overfeeding phytoplankton or bacteria—excess organics cause rapid deterioration
• Consider semi-continuous flow systems for high-density cultures reducing batch water change labor

Challenge: Lower Commercial Availability of Starter Cultures

Problem: Fewer suppliers offer O. nana compared to Acartia, Tigriopus, Tisbe, or Apocyclops

Solutions:

• Search for marine biology research institutions with zooplankton culture programs (universities, government fisheries labs)
• Contact tropical fish hatcheries specializing in grouper, snapper, or ornamental breeding
• Collect wild samples from tropical coastal waters if near suitable habitat (requires species identification expertise)
• Network through aquaculture conferences, industry associations, online forums
• Once obtained, maintain backup cultures in multiple locations for redundancy
• Share cultures with other facilities creating regional cooperative networks

Advantages for Specialized Applications

Smallest Practical Copepod Live Feed: O. nana provides nauplii (60-80μm) smaller than most rotifer strains, allowing successful first-feeding for species with very small larvae that struggle with 100-150μm rotifers.

Perfect Tropical Temperature Match: Thrives at 24-28°C optimal for tropical groupers, snappers, coral reef ornamentals. No temperature compromise balancing copepod vs fish larvae requirements.

Extended Lifespan in Aquariums: Adults survive 2-4 months in reef aquarium refugiums, providing sustained production with less frequent restocking versus short-lived rotifers (2-3 weeks).

Authentic Tropical Planktonic Prey: Tropical reef fish larvae naturally feed on Oithona species in ocean environments. Instinctive recognition and feeding behaviors evolved for this prey type.

SPS Coral Nutrition: Ultra-small size (60-600μm across life stages) perfect match for tiny-polyp Acropora, Montipora, Pocillopora. Improves growth, coloration, stress resistance.

Biodiversity Enhancement: Establishing O. nana in refugiums increases zooplankton diversity creating complex planktonic communities benefiting entire reef ecosystem.

Lower Food Requirements: Ambush-feeding strategy requires less phytoplankton than actively swimming copepods. Can maintain populations in lower-food conditions.

Flexible Diet: Feeds on bacteria, phytoplankton, and microzooplankton providing multiple culture options.

Limitations and Practical Considerations

Slower Reproduction: Generation time 20-30 days (vs 8-18 days for Acartia, Parvocalanus, or harpacticoids) requires larger culture volumes and advance planning.

Lower Per-Liter Yields: Standing densities and harvest rates 30-50% lower than faster-reproducing species, necessitating 2-3x larger culture infrastructure.

Nearly Invisible: Transparent appearance provides poor visual feedback in aquariums. Not ideal for species requiring high-contrast prey (mandarins, seahorses, pipefish).

More Complex Feeding: Best results require multi-trophic approach (phytoplankton + microzooplankton + bacteria) versus simple phytoplankton-only protocols for Acartia.

Limited Commercial Availability: Fewer suppliers offer starter cultures compared to industry-standard species.

Specialized Application: Ultra-small size advantage only relevant for specific applications (ultra-small larvae, tiny-polyp corals, nano fish). Not general-purpose live feed.

Higher Technical Skill: Successful culture requires understanding of diverse feeding strategies, careful water quality management, patient population building.

Ideal Applications for Oithona nana

Highly Recommended For:

• Tropical fish hatcheries targeting species with very small larvae (<2.5mm first-feeding: certain groupers, snappers, angelfish, butterfly fish)
• Ornamental marine fish breeding programs for high-value coral reef species
• Research institutions studying tropical zooplankton ecology, larval fish feeding behavior, or prey size selection
• SPS coral propagation facilities focusing on Acropora, Montipora, and other tiny-polyp species
• Public aquariums with tropical reef exhibits requiring authentic ultra-small zooplankton
• Advanced reef aquarium hobbyists seeking maximum biodiversity in refugium ecosystems

Not Recommended For:

• General commercial fish hatcheries seeking maximum production efficiency (use Acartia, Parvocalanus, or Apocyclops instead)
• Cold-water or temperate fish culture (use O. similis or Acartia)
• Primary food for mandarins, seahorses, pipefish, or other species requiring high-contrast visible prey (use Tigriopus, Tisbe)
• Beginner aquaculturists seeking easy first copepod culture experience (start with Tigriopus californicus or Apocyclops panamensis)
• Operations requiring rapid production startup (<6 weeks)
• Facilities without capacity for multi-trophic feeding approaches

Best Results When:

• Combined with complementary copepod species (Tigriopus for visibility, Tisbe or Apocyclops for medium size)
• Used for specialized applications where ultra-small size provides unique irreplaceable value
• Culturist has experience with other copepod species and ready to advance to more complex protocols
• Infrastructure already supports tropical temperatures (25-28°C) for target fish or corals
• Production timeline allows 2-3 months for population establishment before harvest needs