# Trout Hatchery Operations: Egg Incubation, Fry Rearing, and Smolt Production ## Key Takeaways - Precise water quality management is paramount throughout trout hatchery operations, with critical parameters including dissolved oxygen (>8 mg/L for eggs, >7 mg/L for fry), total ammonia nitrogen (<0.02 mg/L for fry), and nitrite (<0.1 mg/L). Temperature stability within 1°C of the target range (8-12°C for incubation, 10-16°C for growth) is essential to prevent developmental abnormalities and stress. - Egg incubation requires careful control of water flow (1-2 L/min per liter of eggs in vertical incubators) and disinfection protocols, such as iodophor treatment (100 ppm for 10-15 minutes), to mitigate pathogen loads and prevent fungal spread from dead eggs. - Fry rearing necessitates meticulous first-feeding management with appropriate starter feed particle sizes (0.3-0.5 mm) and frequent small feedings (8-12 times daily), alongside regular grading (every 2-4 weeks) to minimize cannibalism and ensure uniform growth. - Smolt production involves physiological preparation for seawater transfer through photoperiod manipulation (18-24 hours light for 6-8 weeks) and specialized diets (42-48% protein, 20-25% fat, 6-10% salt), with salinity tolerance testing (survival >95% in 30-35 ppt seawater for 24-48 hours) as a critical readiness indicator. - Biosecurity measures, including quarantine protocols for new fish, disinfection of equipment, and strict visitor access, are vital to prevent disease introduction and spread, with professional escalation criteria for contacting a fish health veterinarian triggered by mortality exceeding 1% per day for two consecutive days or non-responsive disease outbreaks. --- Trout hatchery operations require precise control of water quality, temperature, and feeding protocols from egg incubation through smolt production. This article provides practical guidance for rainbow trout (*Oncorhynchus mykiss*) and other salmonid hatchery managers, covering egg incubation methods, fry rearing, grading, and smoltification processes. The content draws on established aquaculture practices and peer-reviewed research to support operational decisions. ## At a Glance | Life Stage | Key Management Focus | Typical Duration | Critical Parameters | |------------|---------------------|------------------|---------------------| | Egg incubation | Water flow, temperature stability, disinfection | 3-6 weeks (species dependent) | Dissolved oxygen >8 mg/L, temperature 8-12°C, light exclusion | | Fry rearing | First feeding, feed particle size, grading | 8-12 weeks | Water exchange rate, [feed conversion ratio](/knowledge/animal-farming/poultry/feed-conversion-ratio-measuring-improving-poultry-efficiency), stocking density | | Smolt production | Photoperiod manipulation, salinity tolerance | 4-8 months | Day length, water temperature, feed composition | ## Egg Incubation Methods ### Incubation System Selection Trout egg incubation typically uses either vertical stack incubators (Heath-type) or horizontal trough systems. Vertical stack incubators allow high-density egg loading in a compact footprint, with water flowing upward through stacked trays. Horizontal trough systems provide easier access for egg inspection and removal of dead eggs. The choice depends on hatchery scale, water supply characteristics, and labor availability. The Food and Agriculture Organization of the United Nations provides guidance on cultured species management through its fisheries and aquaculture resources (www.fao.org/fishery/en/culturedspecies). ### Water Quality and Flow Management Egg survival depends on consistent water quality. Dissolved oxygen must remain above 8 mg/L at the egg surface. Water flow rates should provide at least 1-2 L/min per liter of eggs in vertical incubators. Temperature stability within 1°C of the target range (typically 8-12°C for rainbow trout) reduces developmental abnormalities. Sudden temperature shifts can cause egg mortality or delayed hatching. The USDA Agricultural Research Service conducts ongoing research on aquaculture production systems, including hatchery water management (www.ars.usda.gov/animal-production-and-protection/aquaculture). ### Disinfection and Disease Prevention Egg disinfection with iodophor solutions at 100 ppm for 10-15 minutes shortly after fertilization reduces surface pathogen loads. This practice targets bacterial and fungal agents that can cause egg losses. Regular removal of dead or fungused eggs prevents spread to healthy eggs. A large-scale, multi-year microbial community survey of a freshwater trout aquaculture facility documented the complex microbial dynamics present in hatchery systems, emphasizing the importance of biosecurity protocols (FEMS microbiology ecology, 2022, pubmed.ncbi.nlm.nih.gov/36047934). ### Egg Handling and Shipping Eggs are sensitive to mechanical shock during the first 24-48 hours after fertilization (the water-hardening period). After this window, eggs can be shipped in oxygenated bags or specialized egg transport containers. Maintain temperature at 4-8°C during transport. Upon arrival, acclimate eggs to hatchery water temperature gradually over 30-60 minutes before placing in incubators. Record egg source, date of fertilization, and transport conditions for each batch. ### Dead Egg Removal and Fungal Control Remove dead eggs daily using manual picking or chemical treatments where permitted. Dead eggs appear opaque white and can develop fungal growth that spreads to adjacent healthy eggs. Maintain water flow to prevent dead egg accumulation. Record daily mortality counts by incubator tray or trough section to identify problem areas early. ## Fry Rearing Protocols ### First Feeding Management Fry begin feeding when they absorb their yolk sac and become free-swimming, typically 7-14 days after hatch. Offer starter feed with particle sizes of 0.3-0.5 mm. Feed small amounts frequently (8-12 times daily) to maintain feed availability without overloading the system. Uneaten feed degrades water quality and promotes bacterial growth. The FAO Animal Production and Health division provides resources on feeding strategies for aquaculture species (www.fao.org/animal-production/en). ### Water Quality Monitoring Fry are sensitive to ammonia and nitrite. Maintain total ammonia nitrogen below 0.02 mg/L and nitrite below 0.1 mg/L. Dissolved oxygen should remain above 7 mg/L. Water exchange rates of 2-4 exchanges per hour in troughs or tanks support these parameters. Monitor temperature daily and adjust flow rates if oxygen declines. Test water quality at least twice daily during the first feeding period. ### Grading and Size Sorting Grade fry when size variation exceeds 20% of the population mean. Use bar graders or manual sorting. Grading stress can be minimized by conducting the process during cooler morning hours and using anesthetic baths if needed. Record size distribution before and after grading to track growth uniformity. Grade every 2-4 weeks during the fry stage, more frequently if cannibalism is observed. ### Stocking Density Guidelines Stocking density affects growth rate and feed conversion. For fry up to 1 gram, densities of 50-100 fish per liter are common in flow-through systems. As fish grow, reduce density to maintain water quality. In recirculating aquaculture systems, densities can be higher but require more intensive water treatment. Evaluation of brook trout production in a coldwater recycle aquaculture system demonstrated the feasibility of closed-loop production for salmonids (Aquacultural Engineering, 2009, doi.org/10.1016/j.aquaeng.2009.06.012). Adjust density based on dissolved oxygen levels and ammonia accumulation. ### Feeding Rates and Frequency Feed at 2-5% of body weight daily for fry, decreasing to 1-2% for larger fish. Divide daily ration into 8-12 feedings for fry and 4-6 feedings for fingerlings. Adjust feeding based on water temperature: reduce by 50% when temperature drops below 8°C or exceeds 18°C. Record feed offered and estimated consumption daily. Observe feeding behavior to detect health problems early. ## Smolt Production ### Smoltification Process Smoltification prepares trout for seawater transfer. This physiological transformation involves changes in gill function, osmoregulation, and behavior. Photoperiod manipulation using artificial lighting can induce smoltification outside natural seasons. Typical protocols use 18-24 hours of light per day for 6-8 weeks, followed by a natural or reduced photoperiod. Maintain water temperature at 10-14°C during conditioning. ### Salinity Tolerance Testing Before seawater transfer, test smolt salinity tolerance by exposing a sample group to 30-35 ppt seawater for 24-48 hours. Survival above 95% indicates readiness. Measure plasma chloride levels or gill Na+/K+-ATPase activity for more precise assessment. Fish that fail salinity tolerance tests require additional freshwater rearing time. Test at least 20-30 fish per production batch. ### Feed Formulation for Smolts Smolt diets contain higher salt content (6-10% salt) to prepare the digestive system for seawater. Feed particle size should match fish mouth size. Feed conversion ratios typically range from 0.8 to 1.2 during smolt production. Monitor feed intake daily and adjust rations based on water temperature and fish activity. Use commercial smolt feeds from reputable manufacturers. ### Health Monitoring During Smoltification Smoltification is a stressful period that increases disease susceptibility. Monitor for signs of bacterial kidney disease, furunculosis, and viral infections. Resurgence of Salmonid Herpesvirus-3 Infection (Epizootic Epitheliotropic Disease) in Hatchery-Propagated Lake Trout in Michigan highlights the importance of disease surveillance in hatchery populations (Journal of aquatic animal health, 2019, pubmed.ncbi.nlm.nih.gov/30681187). Quarantine any fish showing abnormal behavior or lesions. Record daily observations of feeding response, swimming behavior, and external appearance. ## Water Quality Management ### Temperature Control Trout are coldwater species with optimal growth temperatures of 10-16°C. Temperatures above 20°C cause stress and increase disease risk. Use spring water, well water, or chilled recirculation systems to maintain target temperatures. Record temperature at least twice daily at multiple points in the system. Install temperature alarms for early warning of system failures. ### Dissolved Oxygen Management Maintain dissolved oxygen above 7 mg/L at all life stages. Use oxygen supplementation (liquid oxygen or oxygen cones) during high-density production or warm water periods. Monitor oxygen levels continuously with probes or handheld meters. Low oxygen events require immediate action: increase water flow, reduce feeding, or add supplemental oxygen. Record oxygen levels at least twice daily. ### Ammonia and Nitrite Control Total ammonia nitrogen should remain below 0.02 mg/L for fry and 0.05 mg/L for larger fish. Nitrite below 0.1 mg/L prevents methemoglobinemia (brown blood disease). In recirculating systems, maintain biofilter function through proper temperature, pH (6.5-8.0), and alkalinity (50-150 mg/L as CaCO3). Test water weekly at minimum, daily during high-density production. Record all test results with date and time. ### pH and Alkalinity pH should remain between 6.5 and 8.0. Alkalinity above 50 mg/L buffers against pH swings. Low alkalinity water (soft water) requires buffering with sodium bicarbonate or calcium carbonate. Record pH and alkalinity weekly and after any water source changes. Sudden pH drops indicate biofilter problems or organic loading. ## Feeding and Nutrition ### Feed Selection by Life Stage | Life Stage | Feed Type | Protein Content | Fat Content | |------------|-----------|-----------------|-------------| | Fry (0-1 g) | Starter crumble | 50-55% | 15-18% | | Fingerling (1-20 g) | Grower pellet | 45-50% | 18-22% | | Smolt (20-100 g) | Smolt diet | 42-48% | 20-25% | ### [Feed Conversion Ratio](/knowledge/animal-farming/poultry/feed-conversion-ratio-measuring-improving-poultry-efficiency) Tracking Calculate feed conversion ratio (FCR) as feed offered divided by weight gain. Target FCR of 0.8-1.2 for trout under optimal conditions. Higher FCR indicates feed waste, poor water quality, or disease. Investigate and correct causes of elevated FCR promptly. Track FCR weekly by tank or production unit. ### Nutritional Deficiencies Signs of nutritional deficiencies include poor growth, fin erosion, color loss, and increased mortality. Ensure feed contains adequate vitamins (especially C and E) and minerals (phosphorus, selenium). Use commercial feeds from reputable manufacturers. Store feed in cool, dry conditions and use within 3 months of manufacture. Record feed batch numbers and manufacture dates. ### Feeding Behavior Observation Observe fish during feeding to detect health problems. Healthy trout actively compete for feed. Reduced feeding response indicates stress, disease, or poor water quality. Record feeding behavior daily as normal, reduced, or absent. Investigate any change lasting more than 24 hours. ## Disease Prevention and Biosecurity ### Quarantine Protocols Quarantine all new fish for at least 30 days before introducing to the main population. Use separate equipment and staff for quarantine areas. Monitor quarantined fish daily for signs of disease. The USDA National Agricultural Library provides resources on animal health and welfare practices for aquaculture operations (www.nal.usda.gov/animal-health-and-welfare). Record all observations during quarantine. ### Vaccination Programs Vaccinate against common bacterial diseases such as enteric redmouth (ERM) and furunculosis. Administer vaccines by injection or immersion according to manufacturer instructions. Record vaccination dates, batch numbers, and fish size at vaccination. Boosters may be needed for long production cycles. Consult a fish health veterinarian for vaccination schedules. ### Common Disease Signs Monitor for these signs daily: - Reduced feed intake - Lethargy or abnormal swimming - Skin lesions or fin erosion - Exophthalmia (pop-eye) - Gill pallor or discoloration - Abdominal swelling - Increased respiratory rate ### Biosecurity Measures Implement these biosecurity practices: - Footbaths with disinfectant at facility entrances - Dedicated equipment for each production unit - Restricted visitor access - Disinfection of eggs and equipment - Dead fish removal and proper disposal - Hand washing between tanks ### Professional Escalation Criteria Contact a fish health veterinarian or diagnostic laboratory when: - Mortality exceeds 1% per day for two consecutive days - Multiple fish show the same clinical signs - Disease does not respond to standard treatments - Unusual lesions or behavior appear - Suspected notifiable disease (report to authorities) ## Records and Measurements ### Daily Records Maintain these daily records: - Water temperature (minimum and maximum) - Dissolved oxygen levels - Feed offered and estimated consumption - Mortality count and cause (if known) - Water flow rates - Observations of fish behavior and health ### Weekly Records Record weekly: - Total ammonia nitrogen and nitrite - pH and alkalinity - Average fish weight (sample 20-30 fish) - Feed conversion ratio - Grading results and size distribution ### Monthly Records Compile monthly: - Total production (kg or number of fish) - Cumulative mortality percentage - Feed usage and cost - Water usage - Disease treatments and outcomes ### Record Keeping Systems Use paper logs or digital spreadsheets. Digital systems allow easier data analysis and trend identification. Back up records regularly. Review records weekly to identify emerging problems. Include notes on equipment maintenance and repairs. ## Common Failure Patterns ### Egg Incubation Failures Common causes of egg mortality include: - Temperature fluctuations exceeding 2°C - Low dissolved oxygen (<6 mg/L) - Fungal infection spreading from dead eggs - Mechanical shock during handling - Poor water quality (ammonia, nitrite) ### Fry Rearing Problems Fry losses often result from: - Overfeeding causing water quality deterioration - Underfeeding causing starvation and cannibalism - Inadequate grading leading to size variation - Temperature stress from rapid changes - Disease introduction from contaminated equipment ### Smolt Production Issues Smoltification failures include: - Incomplete smoltification due to improper photoperiod - Poor salinity tolerance from inadequate conditioning - Disease outbreaks during the stress period - Nutritional deficiencies from improper feed - Water quality deterioration at high densities ### Water Quality Crises Water quality emergencies can arise from: - Pump or aeration failure - Power outage affecting water supply - Algal blooms in source water - Biofilter failure in recirculating systems - Chemical contamination from nearby activities ## Welfare and Safety Context ### Fish Welfare Considerations Good welfare practices improve production outcomes. Provide adequate space, water quality, and nutrition. Minimize handling stress through proper equipment and protocols. Use anesthetics when procedures cause significant stress. The USDA National Agricultural Library offers resources on animal welfare standards for aquaculture (www.nal.usda.gov/animal-health-and-welfare). Monitor fish behavior and appearance daily as welfare indicators. ### Worker Safety Hatchery work involves hazards including: - Wet floors causing slips and falls - Heavy lifting of feed bags and equipment - Electrical equipment near water - Chemical handling (disinfectants, anesthetics) - Cold water exposure Provide appropriate personal protective equipment (non-slip boots, gloves, eye protection). Train workers on safe chemical handling and emergency procedures. Post emergency contact numbers prominently. Conduct regular safety inspections. ### Food Safety Considerations For hatcheries producing fish for human consumption, follow food safety protocols: - Use approved feeds and medications - Observe withdrawal periods for treatments - Maintain clean facilities and equipment - Keep records of all treatments and feed sources - Follow Hazard Analysis Critical Control Point (HACCP) principles ### Environmental Management Hatchery operations can affect local water bodies through effluent discharge. Manage waste through: - Solids removal (settling basins, drum filters) - Nutrient management (reduce feed waste) - Water reuse or recirculation - Compliance with discharge permits Stable isotope tracing of trout hatchery carbon to sediments and foodwebs of limestone spring creeks demonstrated that hatchery-derived organic matter can influence downstream ecosystems (The Science of the total environment, 2008, pubmed.ncbi.nlm.nih.gov/18674799). Monitor effluent quality regularly. ## Practical Decision Framework for Hatchery Water Source Selection and Contingency Planning Water source selection is one of the most consequential decisions in trout hatchery operations, affecting egg survival, fry growth, disease prevalence, and overall production costs. Each water source type presents distinct advantages and limitations that require systematic evaluation before construction or expansion. This section provides a structured decision framework for comparing water sources, establishing contingency plans, and implementing monitoring protocols that protect production continuity. ### Water Source Comparison and Selection Criteria Trout hatcheries typically rely on one of three primary water sources: spring water, well water, or surface water from streams or reservoirs. Spring water offers stable temperature year-round, typically 8-12°C, and consistent water quality with low pathogen loads. Well water provides similar temperature stability but may require degassing to remove supersaturated nitrogen or carbon dioxide. Surface water sources are more variable in temperature and quality but often provide higher flow volumes at lower pumping costs. The Food and Agriculture Organization of the United Nations provides guidance on water quality requirements for cultured species through its fisheries and aquaculture resources (www.fao.org/fishery/en/culturedspecies). When evaluating potential water sources, measure these parameters over at least 12 months to capture seasonal variation: temperature range, dissolved oxygen, pH, alkalinity, total hardness, ammonia, nitrite, nitrate, iron, manganese, and turbidity. Record measurements monthly and identify the lowest and highest values for each parameter. For spring and well water sources, test flow rate during the driest period of the year to confirm adequate supply for maximum production capacity. A hatchery producing 50,000 kg of trout annually typically requires 500-1000 L/min of water flow, depending on stocking density and water temperature. Surface water sources require additional testing for upstream land use activities, agricultural runoff, and potential contamination events. ### Contingency Planning for Water Supply Disruption Water supply interruption is the most critical emergency in trout hatchery operations. Develop a written contingency plan that addresses pump failure, power outage, source water contamination, and drought conditions. The USDA Agricultural Research Service conducts research on aquaculture production systems, including water management strategies (www.ars.usda.gov/animal-production-and-protection/aquaculture). For pump failure or power outage, install backup generators capable of running all water pumps and aeration equipment. Test generators weekly under load and maintain fuel supply for at least 48 hours of continuous operation. Install low-flow alarms on main water supply lines that alert staff immediately when flow drops below minimum thresholds. Document alarm set points and response procedures in the hatchery operations manual. For source water contamination events, maintain an alternative water source or storage reservoir. A minimum of 24 hours of water storage capacity allows time to identify contamination sources and implement corrective actions. If contamination is suspected, stop water flow from the affected source and switch to backup supply. Test water quality before resuming normal operations. Record all contamination events with date, time, suspected cause, and corrective actions taken. ### Water Treatment Decision Matrix The need for water treatment depends on source water quality and hatchery production goals. Use this decision matrix to evaluate treatment requirements: | Water Quality Issue | Treatment Option | Application Point | Monitoring Frequency | |---------------------|------------------|-------------------|---------------------| | Supersaturated nitrogen | Degassing column or packed tower | Before egg incubation | Weekly during stable conditions, daily after system changes | | High iron or manganese | Settling basin or mechanical filtration | Before main supply | Monthly, more frequently if staining observed | | Variable temperature | Mixing with groundwater or chilling system | Before distribution | Daily at multiple points | | High turbidity | Sand filtration or drum filtration | Before egg and fry tanks | Continuous with turbidity meter | | Pathogen presence | UV sterilization or ozone treatment | After filtration, before distribution | Weekly UV intensity or ozone residual | The FAO Animal Production and Health division provides resources on water treatment technologies for aquaculture (www.fao.org/animal-production/en). When selecting treatment equipment, consider capital cost, operating cost, maintenance requirements, and impact on water chemistry. UV sterilization is effective against bacteria and viruses but requires low turbidity water. Ozone treatment provides broader disinfection but requires careful monitoring to avoid fish toxicity. ### Water Quality Monitoring Protocol for Source Water Establish a baseline water quality profile for each water source used in the hatchery. Test all parameters monthly for the first year of operation, then quarterly for established sources. Record results in a standardized format that allows year-to-year comparison. The USDA National Agricultural Library provides resources on water quality monitoring for animal production systems (www.nal.usda.gov/animal-health-and-welfare). For surface water sources, increase monitoring frequency during spring runoff and after heavy rainfall events. Test for agricultural chemicals, heavy metals, and bacterial indicators during these periods. If upstream land use changes occur, conduct additional testing to assess impacts on hatchery water quality. ### Emergency Response Procedures Develop written emergency response procedures for these scenarios: - Complete water loss: Shut off feed, reduce stocking density if possible, and transfer fish to backup water source. If no backup is available, consider emergency harvest or fish salvage operations. - Temperature excursion above 20°C: Reduce feeding by 50-75%, increase water exchange rate, add supplemental oxygen, and monitor dissolved oxygen hourly. If temperature exceeds 22°C for more than 4 hours, contact a fish health veterinarian. - Chemical contamination: Stop water flow from contaminated source, flush system with clean water, and test water quality before resuming normal operations. Report contamination events to environmental authorities if required by local regulations. - Disease outbreak linked to water quality: Isolate affected production units, increase water exchange, and contact a fish health veterinarian. Record all water quality parameters from the 48 hours preceding the outbreak. Post emergency contact numbers prominently in all production areas. Conduct emergency response drills quarterly with all hatchery staff. Review and update emergency procedures annually based on drill outcomes and changes in hatchery infrastructure. ### Records and Measurements for Water Source Management Maintain these records for each water source: - Daily: Flow rate, temperature, dissolved oxygen - Weekly: pH, alkalinity, total ammonia nitrogen - Monthly: Complete water quality profile including metals, hardness, and bacterial indicators - Annually: Flow rate during driest period, temperature range, and comparison to baseline profile Review water source records monthly to identify trends or emerging problems. Investigate any parameter that deviates more than 20% from the baseline average. Record all water treatment system maintenance activities with date, equipment serviced, and parts replaced. ### Professional Escalation Criteria for Water Quality Issues Contact a water quality specialist or extension aquaculture specialist when: - Source water temperature exceeds 18°C for more than 7 consecutive days - Dissolved oxygen in source water drops below 6 mg/L - pH drops below 6.0 or exceeds 8.5 - Total ammonia nitrogen in source water exceeds 0.1 mg/L - Unexplained fish mortality coincides with water quality changes - Suspected groundwater contamination from nearby agricultural or industrial activities Early consultation with specialists can prevent production losses and identify corrective actions before problems escalate. Maintain contact information for water testing laboratories and extension specialists in the hatchery operations manual. ## Frequently Asked Questions ### What is the optimal water temperature for rainbow trout egg incubation? Rainbow trout eggs incubate best at 8-12°C. Temperatures below 6°C slow development and increase fungal risk. Temperatures above 14°C cause developmental abnormalities and higher mortality. Maintain temperature within 1°C of the target throughout incubation. Record temperature hourly during critical periods. ### How often should I grade trout fry? Grade fry when size variation exceeds 20% of the population mean. This typically occurs every 2-4 weeks during the fry stage. More frequent grading may be needed if cannibalism is observed. Record size distribution before and after each grading event. Grade during cooler morning hours to reduce stress. ### What is the typical feed conversion ratio for trout smolts? Target feed conversion ratio for trout smolts is 0.8-1.2 under optimal conditions. Higher ratios indicate feed waste, poor water quality, or health problems. Track FCR weekly and investigate deviations from target. Adjust feeding rates based on water temperature and fish activity. ### How do I induce smoltification in rainbow trout? Use photoperiod manipulation with 18-24 hours of light per day for 6-8 weeks, followed by natural or reduced photoperiod. Maintain water temperature at 10-14°C during conditioning. Feed smolt diets containing 6-10% salt. Test salinity tolerance before seawater transfer. Monitor fish behavior and appearance throughout the process. ### What are the signs of incomplete smoltification? Signs include poor salinity tolerance (survival below 95% in 24-hour seawater challenge), reduced growth after transfer, and behavioral changes such as remaining near the water surface. Fish that fail salinity tolerance tests require additional freshwater rearing time. Retest after 2-4 weeks of additional conditioning. ### How do I prevent fungal infections on trout eggs? Remove dead eggs promptly to prevent fungal spread. Use egg disinfection with iodophor solutions at 100 ppm for 10-15 minutes after fertilization. Maintain good water flow around eggs. Formalin treatments may be used under veterinary guidance where permitted. Record all treatments with date, concentration, and duration. ### What water quality parameters are critical for trout fry? Maintain dissolved oxygen above 7 mg/L, total ammonia nitrogen below 0.02 mg/L, nitrite below 0.1 mg/L, pH between 6.5 and 8.0, and temperature at 10-16°C. Test water quality daily for fry tanks. Adjust water exchange rates to maintain these parameters. Record all test results with date and time. ### When should I contact a fish health veterinarian? Contact a veterinarian when mortality exceeds 1% per day for two consecutive days, multiple fish show the same clinical signs, disease does not respond to standard treatments, unusual lesions or behavior appear, or a notifiable disease is suspected. Early intervention improves treatment outcomes. Keep contact information for diagnostic laboratories readily available. ## Related Farming Guides - __MASK_1__ - __MASK_2__ - __MASK_3__ - __MASK_4__ - __MASK_5__ ## Related Clinical & Scientific Guides * [Pond Sediment Management and Dredging Options](/knowledge/animal-farming/aquaculture/pond-sediment-management-dredging-options) * [Indoor Aquaculture Facilities: Lighting and Insulation](/knowledge/animal-farming/aquaculture/indoor-aquaculture-facilities-lighting-insulation) * [Greenhouse Aquaculture: Extending Growing Seasons](/knowledge/animal-farming/aquaculture/greenhouse-aquaculture-extending-growing-seasons) ## References and Further Reading - __MASK_6__ - __MASK_7__ - __MASK_8__. Food and Agriculture Organization of the United Nations. - __MASK_9__. USDA National Agricultural Library. - __MASK_10__. FEMS microbiology ecology, 2022. - __MASK_11__. Journal of fish biology, 2026. - __MASK_12__. Journal of aquatic animal health, 2019. - __MASK_13__. The Science of the total environment, 2008. - __MASK_14__. Frontiers in genetics, 2024. - __MASK_15__. The Journal of heredity, 2018. - __MASK_16__. Ceur Workshop Proceedings, 2022. - __MASK_17__. Aquaculture, 1996. - __MASK_18__. Aquacultural Engineering, 2009. - __MASK_19__. Aquaculture and Conservation of Inland Coldwater Fishes, 2024. > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.