# Harvesting Systems for Aquaculture: Nets, Pumps, and Grading ## Key Takeaways - Harvest method selection is dictated by scale and species; seine nets are optimal for ponds under 1 acre, while fish pumps are essential for operations exceeding 5,000 pounds per hour, with vacuum pumps offering gentleness over impeller pumps for sensitive species. - Grading should be a post-harvest process, as concurrent grading with pumping significantly elevates fish stress and mortality; bar graders are cost-effective for width-based sorting, while weight graders offer superior accuracy for high-value species. - Critical water quality parameters during harvest include maintaining dissolved oxygen above 5 ppm and avoiding temperatures above 85°F for warmwater species to mitigate rapid depletion and increased metabolic demand, respectively. - Partial harvests, common for species with asynchronous growth like catfish and tilapia, require meticulous handling to protect remaining stock, necessitating careful net mesh selection to allow smaller individuals to escape. - Pathogen transmission is a significant risk; all harvest equipment must be thoroughly cleaned and sanitized between ponds and farms, and harvest data, including mortality and grade distribution, is crucial for informing future stocking and management decisions. - Pre-harvest veterinary consultation is imperative when observing signs of disease, such as lethargy, lesions, or abnormal swimming, to prevent disease spread and ensure food safety. --- Harvesting fish is one of the most stressful events in the production cycle, both for the fish and for the farmer. A poorly planned harvest can damage market value through bruising, scale loss, or mortality, and it can set back the health of remaining stock if you are doing a partial harvest. This guide covers the full range of fish harvesting systems, from simple seine nets for small ponds to high-capacity fish pumps and automated grading lines for commercial operations. It is written for aquaculture producers, farm managers, extension agents, and students who need practical, actionable information on choosing, operating, and maintaining harvest equipment. You will learn how to match the harvest method to your species, facility type, and production volume, how to run each system safely and efficiently, and how to avoid the common mistakes that cost time and money. ## At a Glance - Match the harvest method to your scale: small ponds under 1 acre are best served by seine nets and brails, while operations moving more than 5,000 pounds per hour should invest in fish pumps. - Grading should happen after harvest, not during it. Running fish through graders at the same time as pumping increases stress and mortality. - Water quality during harvest is critical. Oxygen levels drop quickly when fish are crowded in a net or holding tank, so have supplemental aeration ready before you start. - Partial harvests remove the largest fish and leave the rest growing. This works well for catfish, tilapia, and hybrid striped bass but requires careful handling to protect the fish that stay in the pond. - Fish pumps come in three main types: vacuum, impeller, and airlift. Vacuum pumps are gentle but slow, impeller pumps are fast but harder on fish, and airlift pumps are the gentlest but have the lowest capacity. - Grading equipment ranges from simple bar graders to complex drum and vibratory sorters. The right choice depends on whether you grade by length or by weight. - Clean and sanitize all harvest equipment between ponds and between farms to prevent the spread of pathogens. - Record harvest data including total weight, count, mortality, grade distribution, and water temperature. This data drives future stocking decisions. - Call your veterinarian or extension agent before harvest if you see signs of disease, low oxygen, or unusual behavior in the fish. Harvesting stressed or sick fish can spread disease and reduce [food safety](/knowledge/bacteria/livestock-bacteria/cooking-chicken-bacteria-prevention). ## Planning the Harvest Harvesting is not a single event. It is a process that starts weeks before you pull the first net. Good planning protects your fish, your equipment, and your profit. ### Determine the Harvest Type You need to decide whether you are doing a complete harvest or a partial harvest. A complete harvest removes all fish from the pond or tank. This is standard for ponds that need to be drained, renovated, or rested. It is also used when all fish have reached market size and you want to reset the production cycle. Complete harvests are stressful because the fish are crowded into a small area as the water level drops, and you must handle every fish. A partial harvest, also called a selective harvest, removes only the largest fish. The remaining fish continue to grow. This is common in catfish and tilapia production where fish grow at different rates. Partial harvests allow you to generate cash flow throughout the season and reduce the risk of overcrowding as fish grow. The downside is that partial harvests require more careful handling because the fish that remain in the pond must not be injured or overly stressed. ### Assess Fish Readiness Do not harvest fish that are not ready. Check the size distribution before you schedule the harvest. Sample the fish using a small seine or cast net to estimate the average weight and the range of sizes. If you are harvesting for a specific market, such as a restaurant that wants 1.5 pound fish, make sure the majority of the population is at or above that target. Check the condition of the fish. Fish that appear lethargic, have visible lesions, or are swimming abnormally should not be harvested for food. If you see signs of disease, contact your veterinarian before proceeding. ### Check Weather and Water Conditions Weather matters more than most farmers realize. Harvesting during extreme heat increases stress and mortality. Harvesting during storms is dangerous for workers and can muddy the water, which reduces visibility and increases the chance of gill damage from sediment. The ideal harvest day has mild temperatures, light wind, and stable barometric pressure. Water temperature should be within the normal range for your species. For warmwater species like catfish and tilapia, water temperatures below 85 degrees Fahrenheit are preferable. For coolwater species like trout, keep water temperatures below 65 degrees Fahrenheit during harvest. ### Prepare Equipment and Supplies Make a checklist and run through it before you start. You will need: - Harvest nets appropriate for your pond size and fish size - Holding tanks or live cars with aerated water - Grading equipment if you are separating sizes - Transport tanks with oxygen and aeration systems - Ice or chilled water for fish that will be processed immediately - First aid kit for workers - Communication devices such as radios or phones - Backup oxygen tanks and aerators - Clean clothing and boots for workers - Sanitizing solutions for equipment between ponds Inspect all equipment before the harvest day. A torn net or a failing pump seal can ruin a harvest and endanger your fish. ### Schedule the Harvest Time of day matters. Early morning is the best time to harvest in most situations. Water temperatures are cooler, oxygen levels are often higher, and you have the full day ahead to complete the work. Avoid harvesting in the heat of the afternoon when fish are already stressed by warm water and lower dissolved oxygen. Plan for the harvest to take longer than you expect. Rushing increases mistakes and fish stress. Build in extra time for equipment failures, weather changes, and unexpected fish numbers. ## Harvesting with Nets Nets are the oldest and most versatile harvest tool in aquaculture. They work for small ponds, large ponds, raceways, and cages. The key is choosing the right net for your situation and using it correctly. ### Seine Nets Seine nets are the standard for pond harvests. A seine is a long net with floats on the top line and weights on the bottom line. You pull it through the water to encircle fish and guide them toward a collection area. The mesh size of the seine determines what you catch. Small mesh catches all fish but creates more drag and is harder to pull. Large mesh allows small fish to escape, which is useful for partial harvests. For example, a 1 inch mesh seine will hold most fish over 6 inches, while a 1.5 inch mesh will let smaller fish pass through. Seine length should be about 1.5 times the width of the pond. This allows the net to sweep the full width and maintain a proper pocket for collecting fish. A net that is too short leaves gaps at the edges. A net that is too long is difficult to manage and can tangle. Seine depth should be at least 1.5 times the deepest water you will harvest. The bottom line needs to stay on the pond bottom even when the net forms a pocket with fish in it. If the net is too shallow, fish will escape over the top. #### How to Run a Seine Harvest 1. Position the seine at one end of the pond. Attach the tow lines to a vehicle, a winch, or a team of workers, depending on the pond size. 2. Set the net in the water with the floats up and the weights down. Make sure the bottom line is fully on the pond bottom before you start pulling. 3. Pull the seine slowly and steadily toward the collection end of the pond. A slow pull keeps the net on the bottom and allows fish to swim ahead of the net rather than trying to jump over it. 4. As the net approaches the shallow end, begin to close the gap between the two ends. This forms a pocket that concentrates the fish. 5. Once the fish are concentrated, use brails or dip nets to remove them from the seine pocket. Work quickly but carefully to avoid injuring fish. 6. Transfer fish to holding tanks or grading equipment immediately. Do not let fish sit in the net pocket longer than necessary. The biggest mistake in seine harvesting is pulling too fast. A fast pull lifts the bottom line off the pond bottom, allowing fish to escape underneath. It also increases the chance of tearing the net on stumps, rocks, or other obstructions. ### Brails and Dip Nets Brails are large scoop nets with a rigid frame. They are used to lift fish out of a seine pocket or a holding area. A brail is essentially a big dip net, and it comes in many sizes. Small brails for fingerlings might have a 12 inch opening. Large brails for food fish can have a 4 foot opening and require two workers to operate. The mesh of a brail should be fine enough to hold the smallest fish you are harvesting, but large enough to allow water to drain quickly. A brail that holds too much water is heavy and difficult to lift. When using a brail, lower it gently into the water beside the fish. Do not chase fish with the brail. Instead, guide fish into the brail using a smaller hand net or by moving the seine pocket to concentrate fish in one spot. Lift the brail straight up, allow the water to drain, and then tilt it to deposit the fish into a holding tank or grading bin. ### Cast Nets Cast nets are small circular nets with weights around the edge. They are used for sampling and for harvesting in small, shallow ponds where a seine is impractical. A skilled operator can throw a cast net to cover an area of 50 to 100 square feet. Cast nets are not efficient for large-scale harvests. They are best used for checking fish size, estimating population, or catching broodstock. If you find yourself using a cast net for a commercial harvest, you likely need a better system. ### Gill Nets and Trap Nets Gill nets catch fish by entangling them behind the gills. They are selective by mesh size and are sometimes used for removing specific size classes of fish. However, gill nets cause high stress and injury to fish, and they are not recommended for harvesting food fish that will be sold live or fresh. Fish caught in gill nets are often dead or severely stressed by the time you retrieve the net. Trap nets are stationary nets that guide fish into a holding chamber. They are used more for wild capture fisheries than for aquaculture. In aquaculture, trap nets are occasionally used in raceways or channels where fish move in a predictable pattern. They are not a primary harvest tool for most operations. ### Net Harvesting by Facility Type **Ponds:** Seine nets are the standard. For ponds larger than 5 acres, consider using a mechanical winch to pull the seine. For ponds under 1 acre, a four person crew can pull the seine by hand. **Raceways:** Raceways are narrow and have a strong water flow. The most efficient harvest method is to use a blocking screen at the downstream end and a crowding screen that you move from upstream to downstream. This concentrates the fish at the lower end of the raceway, where you can brail them out or pump them. **Cages:** Cage harvests use dip nets or small brails to lift fish from the cage. For larger cages, you can use a fish pump with a suction hose lowered into the cage. This is faster and less stressful than netting if the pump is properly set up. **Tanks:** Tank harvests depend on the tank design. Some tanks have a drain that allows fish to be flushed into a collection sump. Others require netting or pumping. If your tanks have drains, use them. Draining is the least stressful method because you do not have to chase fish with a net. ## Fish Pump Systems Fish pumps move fish through a pipe using water flow. They are the backbone of modern commercial harvest operations because they move large volumes of fish quickly and with less labor than netting. ### Types of Fish Pumps #### Vacuum Pumps A vacuum pump uses suction to draw fish and water into a holding tank. The tank fills, then the vacuum is released and the fish are discharged through a valve into a grading system or transport tank. Vacuum pumps are the most common type in aquaculture because they are relatively gentle on fish. The fish are never in contact with an impeller or blade. They travel through smooth pipes and are cushioned by water. The main limitation of vacuum pumps is capacity. A typical vacuum pump can move 2,000 to 5,000 pounds of fish per hour, depending on the model and the distance the fish must travel. This is adequate for many operations but can be a bottleneck for large harvests. #### Impeller Pumps Impeller pumps use a rotating blade to create flow that carries fish through the system. They are fast, moving 10,000 to 20,000 pounds per hour or more. However, the impeller can injure fish, especially if the pump is oversized for the fish being moved or if the fish are weak or stressed. Impeller pumps are best for hardy species like catfish and tilapia that are being harvested for processing. They are not suitable for delicate species like trout or for fish that will be sold live. #### Airlift Pumps Airlift pumps inject compressed air into a vertical pipe. The rising air bubbles create an upward flow that carries fish and water to the top of the pipe, where they spill out into a collection trough. Airlift pumps are the gentlest type of fish pump. There are no moving parts in contact with the fish. However, they have the lowest capacity, typically moving 1,000 to 3,000 pounds per hour. They are best for small operations or for moving fish short distances. ### Choosing a Fish Pump Consider these factors when selecting a pump: **Species sensitivity:** Delicate fish need vacuum or airlift pumps. Hardy fish can tolerate impeller pumps. **Harvest volume:** Calculate your peak harvest rate. If you need to move 10,000 pounds in two hours, you need a system that can handle 5,000 pounds per hour. **Distance and elevation:** Pumps lose efficiency over long distances and when lifting fish to a higher elevation. A vacuum pump that moves fish 50 feet may not work at 200 feet. **Fish size:** Large fish need larger pipes and more water flow. A pump designed for 1 pound fish will struggle with 10 pound fish. **Power availability:** Some pumps require three phase power. Others can run on single phase or diesel engines. Match the pump to your site infrastructure. **Budget:** Vacuum pumps are moderately priced. Impeller pumps are cheaper per unit of capacity. Airlift pumps are the least expensive but also the least productive. ### Operating a Fish Pump 1. Set up the pump on stable, level ground. Make sure the discharge pipe directs fish into your grading system or transport tank. 2. Connect the suction hose and place it in the water where the fish are concentrated. The suction intake should be fully submerged but not resting on the bottom. 3. Prime the pump according to the manufacturer instructions. Most pumps require the suction line to be filled with water before startup. 4. Start the pump and adjust the water flow. You want enough flow to carry fish but not so much that fish are tumbling or bouncing through the pipe. 5. Guide fish toward the suction intake using a seine or crowding screen. Fish will not voluntarily swim to the pump intake in large numbers. 6. Monitor the discharge continuously. Watch for signs of injury, such as fish with torn fins, missing scales, or reddened areas on the body. 7. If you see injury, reduce the pump speed or switch to a gentler harvest method. 8. Stop the pump when the desired number of fish has been moved. Do not run the pump dry, as this can damage the seals and impeller. ### Reducing Pump Stress on Fish Fish passing through a pump experience acceleration, pressure changes, and possible contact with pipe walls. You cannot eliminate all stress, but you can reduce it. Use the largest diameter pipe that is practical. Larger pipes allow more water per fish and reduce crowding. A good rule of thumb is to keep the fish density in the pipe below 2 pounds per gallon of water. Keep the suction line as short as possible. Every foot of pipe adds friction and turbulence. Place the pump as close to the harvest area as the layout allows. Ensure the water flow is at least 10 times the volume of fish being moved. If you are pumping 100 pounds of fish per minute, you need at least 1,000 pounds of water per minute of flow. Avoid pumping fish when water temperatures are above 85 degrees Fahrenheit. Warm water holds less oxygen, and the additional stress of pumping can cause mortality. ## Fish Grading Equipment Grading is the process of separating fish by size. It is essential for producing uniform market lots, managing feeding programs, and ensuring that smaller fish are not outcompeted for feed. ### Why Grade Fish Fish grow at different rates. In any population, you will have a range of sizes. Grading allows you to: - Sell fish in uniform size classes that meet market specifications - Feed fish according to size to reduce waste - Reduce competition and cannibalism in species like bass and trout - Manage inventory and predict harvest dates - Identify slow growing fish that may need culling Grading can happen at harvest, when you separate market size fish from submarket fish. It can also happen during the production cycle, when you divide a mixed population into size classes and stock them in separate ponds or tanks. ### Manual Grading The simplest grading method is by hand. Workers pick up fish and sort them by visual assessment or by measuring with a ruler or template. This is slow and subjective, but it is the only option for very large fish or for fish that are too delicate for mechanical graders. Hand grading is practical for operations handling fewer than 1,000 fish per day. It is also used for broodstock and for valuable fish where accuracy matters more than speed. ### Bar Graders Bar graders are the most common mechanical grading tool. They consist of a series of parallel bars with a set spacing. Fish pass over the bars, and fish smaller than the spacing fall through while larger fish continue over the top. Bar graders are simple, inexpensive, and effective for grading by body width. They work best for fish with a round or oval cross section, such as catfish, tilapia, and trout. The spacing between bars determines the grade size. You need to match the spacing to the fish species and the target size. For example, a 1 inch spacing will separate catfish at roughly 0.5 pounds, while a 1.5 inch spacing separates at about 1 pound. Bar graders come in two orientations. In a flat grader, fish move horizontally across the bars. In an inclined grader, the bars are angled so fish slide downward while smaller fish drop through. Inclined graders are faster and require less labor because gravity does the work. ### Drum Graders A drum grader is a rotating cylinder with holes or slots of a specific size. Fish enter one end of the drum and are carried along as it rotates. Fish smaller than the openings fall through, while larger fish continue to the discharge end. Drum graders are more gentle than bar graders because the fish tumble less. They are also more compact, making them suitable for operations with limited space. The main limitation of drum graders is that they are more expensive than bar graders and require power to operate. They are best for operations that grade large volumes of fish on a regular basis. ### Vibratory Graders Vibratory graders use a vibrating screen or deck to move fish across a series of openings. The vibration keeps fish moving and prevents them from clogging the openings. These graders are fast and accurate, but they can be hard on fish. The vibration and the bouncing motion stress fish and can cause scale loss. They are best for hardy species and for fish that will be processed immediately. ### Weight Graders Weight graders are the most accurate type of grader. They weigh each fish individually and route it to the appropriate bin. Modern weight graders can process 3,000 to 10,000 fish per hour with accuracy within a few grams. Weight graders are expensive, often costing tens of thousands of dollars. They are justified only for high value species like salmon, trout, and hybrid striped bass, where size uniformity commands a price premium. ### Choosing a Grading System Match the grader to your species, fish size, volume, and budget. | Factor | Bar Grader | Drum Grader | Vibratory Grader | Weight Grader | |---|---|---|---|---| | Initial cost | Low | Moderate | Moderate | High | | Operating cost | Low | Moderate | Moderate | High | | Capacity | Moderate | High | High | High | | Accuracy | Good | Good | Good | Excellent | | Fish stress | Moderate | Low | High | Low | | Power required | None or minimal | Yes | Yes | Yes | | Best for | Small to medium operations | Medium to large operations | Hardy fish, processing plants | High value species | ### Integrating Grading with Harvest The most efficient operations integrate grading directly into the harvest line. Fish come out of the pond through a pump or net, drop into a holding tank, then flow through a grader and into transport tanks or processing bins. A typical harvest line looks like this: 1. Fish are crowded in the pond using a seine or crowding screen. 2. A fish pump lifts fish from the pond and discharges them into a dewatering screen or holding tank. 3. Fish flow from the holding tank into the grader. 4. Graded fish fall into separate holding tanks or transport vehicles for each size class. 5. Water and debris from the dewatering screen are returned to the pond or filtered. This continuous flow system minimizes handling and keeps fish in water at all times. It is the standard for commercial operations harvesting more than 5,000 pounds per day. ## Holding and Transport Systems Fish that are harvested but not immediately processed need to be held in water with adequate oxygen. The holding system is part of the harvest line and must be planned in advance. ### Live Cars and Floating Cages A live car is a mesh enclosure that floats in the pond or a nearby water body. Fish are held in the live car until they are graded, loaded, or processed. Live cars are simple and inexpensive, but they require water exchange to maintain oxygen levels. Live cars work best for short holding periods of a few hours. If fish will be held overnight, you need supplemental aeration. ### Holding Tanks Holding tanks on land provide more control than live cars. They can be aerated, chilled, and monitored. The tank should be sized to hold the maximum harvest volume with at least 1 pound of fish per gallon of water. Lower densities are better for stressed fish. Holding tanks need continuous aeration. Use air stones, diffusers, or paddle wheels to maintain dissolved oxygen above 5 parts per million. If you are holding fish for more than a few hours, consider a recirculating system with biofiltration to manage ammonia. ### Transport Tanks Transport tanks are mounted on trucks and used to move fish from the farm to a processing plant or to another farm. They must be aerated and insulated to maintain water temperature. Loading density in transport tanks depends on the species, water temperature, and trip duration. A general guideline is 1 to 2 pounds of fish per gallon of water for trips under 4 hours, and 0.5 to 1 pound per gallon for longer trips. Reduce density by half when water temperatures are above 75 degrees Fahrenheit. Oxygen requirements are critical during transport. Most transport tanks use compressed oxygen delivered through diffusers. The oxygen flow should be adjusted based on fish activity and water temperature. A good starting point is 1 liter per minute of oxygen for every 100 pounds of fish. ### Ice and Chilling Fish that will be processed immediately need to be chilled to slow spoilage. The standard is to reduce the fish body temperature to below 40 degrees Fahrenheit as quickly as possible after harvest. The most common method is to add ice to the holding tank or transport tank. Use flake ice or crushed ice, which has more surface area and cools faster than block ice. The ratio of ice to fish depends on the initial water temperature. As a starting point, use 1 part ice to 2 parts fish by weight when water temperatures are above 70 degrees Fahrenheit. Do not add ice directly to tanks holding live fish that will be sold live. Rapid temperature changes can kill fish. Instead, chill only the fish that are destined for processing. ## Water Quality Management During Harvest Harvest is a period of intense stress for fish, and water quality is the most important factor in their survival. Poor water quality during harvest can cause mortality that erases the profit from the harvest. ### Dissolved Oxygen Dissolved oxygen drops rapidly when fish are crowded. A dense school of fish can deplete oxygen in a matter of minutes. You must have supplemental aeration running before you start crowding fish. The target dissolved oxygen during harvest is above 5 parts per million. If oxygen drops below 3 parts per million, fish become stressed and may die. Below 2 parts per million, mortality is likely. Aeration options include: - Paddle wheel aerators placed in the pond near the harvest area - Diffused air systems in holding tanks and transport tanks - Liquid oxygen injection for high density holding - Emergency hydrogen peroxide application for rapid oxygen boost Check oxygen levels every 15 minutes during harvest. Use a dissolved oxygen meter or test kit. Do not rely on visual observation of fish behavior, because fish do not always show obvious signs of oxygen stress until it is too late. ### Temperature Water temperature affects oxygen solubility and fish metabolism. Warmer water holds less oxygen and increases fish oxygen demand. This combination makes summer harvests particularly risky. If water temperatures are above 85 degrees Fahrenheit, consider delaying the harvest until cooler weather. If you must harvest in hot weather, reduce fish density in nets and holding tanks, increase aeration, and work quickly. ### Ammonia and Nitrite Ammonia is excreted by fish through their gills and in their urine. During harvest, ammonia levels can rise quickly because fish are crowded and stressed. Ammonia is more toxic at higher pH and temperature. If you are holding fish for more than an hour, monitor ammonia levels. The safe level of un-ionized ammonia is below 0.02 parts per million. If ammonia is rising, reduce fish density or add clean water to dilute it. Nitrite is a product of ammonia breakdown in biofilters. It is less of a concern during short harvests but becomes important if fish are held for extended periods in recirculating systems. ### Carbon Dioxide Carbon dioxide builds up in the water as fish respire. High carbon dioxide levels reduce the ability of fish to absorb oxygen, even when dissolved oxygen is adequate. Carbon dioxide levels above 20 parts per million are stressful to fish. Above 40 parts per million, fish may show signs of distress. Aeration helps remove carbon dioxide, so maintain vigorous aeration throughout the harvest. ### pH pH can shift during harvest due to respiration and decomposition. The ideal pH for most aquaculture species is between 6.5 and 8.5. If pH drops below 6, fish become stressed. If it rises above 9, ammonia becomes more toxic. Test pH at the start of harvest and periodically during the process. If pH is outside the safe range, delay the harvest or adjust the water chemistry. ## Common Harvest Mistakes and How to Avoid Them Experienced farmers make harvest mistakes too. The most common problems are predictable and preventable. ### Crowding Fish Too Tightly The instinct to get all the fish out at once leads to over crowding. Fish packed too tightly in a net or holding tank suffocate and injure each other. The solution is to harvest in batches. Remove a portion of the fish, rest the remaining fish, then resume harvesting. A good rule of thumb is to keep the fish density in a seine pocket below 2 pounds per gallon of water. In a holding tank, keep density below 1 pound per gallon. ### Pulling the Seine Too Fast A fast seine pull lifts the bottom line off the pond bottom and allows fish to escape. It also creates a bow wave that pushes fish ahead of the net, making them harder to capture. Pull the seine slowly and steadily. If you see fish jumping over the top line, you are pulling too fast. ### Using the Wrong Mesh Size Mesh that is too small creates drag and makes the net hard to pull. Mesh that is too large allows small fish to escape. Match the mesh to the smallest fish you want to keep. If you are harvesting food fish of 1 pound or larger, use a mesh of 1.5 to 2 inches. If you are harvesting fingerlings, use a mesh of 0.25 to 0.5 inches. ### Neglecting Oxygen Monitoring Farmers who have harvested the same pond for years may skip oxygen checks because they have never had a problem. This is a dangerous habit. Oxygen levels vary with weather, time of day, and fish density. Always check oxygen before and during harvest. ### Mixing Fish from Different Ponds Do not mix fish from different ponds during harvest unless you have a reason to do so. Mixing can spread diseases between populations and complicates inventory tracking. If you must mix fish, combine them only after harvest and keep records of which ponds contributed. ### Handling Fish Roughly Rough handling causes scale loss, fin damage, and stress. Fish with damaged skin are more susceptible to infection and have a shorter shelf life. Train workers to handle fish gently and to use wet hands or wet gloves when touching fish. ### Delaying the Transfer to Transport Tanks Fish sitting in a holding tank or live car are not safe. They are using oxygen, producing waste, and accumulating stress. Move fish to transport tanks or processing as quickly as possible. Do not let fish wait while you take a break or handle another task. ### Ignoring Worker Safety Harvest is physically demanding work. Workers can be injured by nets, pumps, and wet surfaces. Provide proper training, safety equipment, and breaks. Have a first aid kit on site and a plan for emergencies. ## Monitoring and Recordkeeping Harvest data is some of the most valuable information you will collect all year. It tells you how well your production system is working and guides future decisions. ### Track These Metrics **Total weight harvested:** The total pounds of fish removed from the pond or tank. **Number of fish harvested:** Count fish during grading or use a sample count to estimate the total. **Average weight:** Divide total weight by total count. This tells you if your fish reached market size. **Grade distribution:** The percentage of fish in each size class. This helps you predict future harvests and adjust feeding. **Mortality:** The number or percentage of fish that died during harvest. High mortality indicates a problem with the harvest method or fish health. **Harvest duration:** How long the harvest took. This helps you plan future harvests and schedule labor. **Water quality data:** Temperature, dissolved oxygen, pH, and ammonia readings taken during harvest. **Equipment issues:** Any equipment failures or problems that occurred during harvest. ### Keep a Harvest Log Create a standardized harvest log form that includes all the metrics listed above. Fill it out for every harvest, even small ones. Store the logs in a binder or digital spreadsheet. At the end of each season, review your harvest logs. Look for trends. Are fish reaching market size on schedule? Are mortality rates increasing? Are certain ponds producing better than others? Use this information to adjust stocking rates, feeding programs, and harvest schedules. ### Use Data for Decision Making Harvest data informs several key decisions: **Stocking rates:** If average harvest weight is below target, reduce stocking density next season. If fish are oversized, increase stocking density. **Feed management:** If grade distribution shows many small fish, you may need to feed more or adjust feed particle size. **Pond management:** If certain ponds consistently produce poor harvests, investigate water quality, aeration, and disease history for those ponds. **Market planning:** If you have a surplus of a particular size class, adjust your marketing strategy or schedule harvests to better match market demand. ## When to Call a Veterinarian or Extension Agent Most harvests go smoothly, but some situations require professional help. Do not hesitate to call for assistance when you see problems. ### Signs That Fish Are Unhealthy Before Harvest Call your veterinarian before harvesting if you observe: - Fish swimming erratically or gasping at the surface - Visible lesions, ulcers, or fungal growth on the skin - Pop eye, which is bulging eyes - Pale gills or gills with visible parasites - Unusual mortality in the days before harvest - Fish that are not feeding normally Harvesting sick fish is risky for several reasons. The stress of harvest can trigger disease outbreaks in the remaining population. Diseased fish may not be suitable for human consumption. And processing plants may reject loads that show signs of disease. Your veterinarian can examine the fish, run diagnostic tests, and advise whether it is safe to harvest. If a disease is confirmed, the veterinarian can recommend treatment or a delay in harvest. ### Signs of Water Quality Problems If oxygen levels are low, ammonia is high, or pH is outside the safe range, call your extension agent for advice. They can help you troubleshoot the cause and recommend corrective action. Extension agents can also help with: - Choosing harvest equipment for your specific operation - Setting up a harvest plan - Interpreting harvest data - Connecting you with other producers who have solved similar problems ### Regulatory and [Food Safety](/knowledge/bacteria/livestock-bacteria/cooking-chicken-bacteria-prevention) Concerns If you suspect that harvested fish may be contaminated with chemicals, drugs, or environmental pollutants, contact your extension agent or the appropriate regulatory authority. Do not sell fish that may be contaminated. If fish show signs of a reportable disease, such as viral hemorrhagic septicemia or infectious salmon anemia, contact your veterinarian and the appropriate animal health authority immediately. The WOAH Aquatic Animal Health Code provides guidance on reporting and managing aquatic animal diseases. ## Frequently Asked Questions ### How do I know which harvest method is right for my operation? Start with your production volume and species. For ponds under 2 acres and harvests under 1,000 pounds, a seine net and brail are sufficient. For larger operations, add a fish pump and grading system. Consider the sensitivity of your species. Trout and salmon need gentle vacuum pumps, while catfish and tilapia tolerate impeller pumps. Match the system to your scale and species, and plan for future growth so you do not have to replace equipment in a few years. ### Can I harvest fish without draining the pond? Yes. Seine nets are the standard method for partial and complete harvests without draining. You can also use fish pumps to remove fish from a crowded area of the pond. Draining is necessary only for complete harvests where you need to renovate the pond bottom, repair structures, or remove all fish including those that evade the net. ### How many workers do I need for a seine harvest? A crew of four to six workers can handle most pond harvests. Two workers manage the net ends, one or two operate the brail, and one or two handle fish transfer to holding tanks. For larger ponds, add workers or use a mechanical winch to pull the seine. The key is to have enough people to work quickly, because speed reduces fish stress. ### What is the fastest way to harvest a large pond? A fish pump with a crowding system is the fastest method for ponds over 5 acres. Use a seine to crowd fish into a small area, then place the pump suction in the crowded zone. A high capacity impeller pump can move 10,000 pounds per hour or more. This method requires fewer workers than netting and reduces handling stress. ### How do I prevent fish from dying during harvest? Maintain dissolved oxygen above 5 parts per million at all times. Use supplemental aeration before you start crowding fish. Keep fish densities low in nets and holding tanks. Work quickly but gently. Do not harvest in extreme heat. Monitor water quality throughout the process and adjust as needed. Most harvest mortality is caused by oxygen depletion and rough handling, both of which are preventable. ### What size grader do I need for my fish? The grader size depends on the target market size and the range of fish sizes in your population. Measure the body width of your target size fish and choose a bar spacing that is slightly smaller than that width. For example, if you want to separate fish at 1 pound and those fish have a body width of 1.5 inches, use a bar spacing of 1.25 to 1.4 inches. Test the grader with a sample of fish before running the full harvest. ### How long can fish stay in a holding tank before processing? Fish can stay in a holding tank for several hours if the water is aerated and the density is low. For periods longer than 4 hours, you need to manage ammonia levels and consider chilling the water. If fish will be held overnight, use a recirculating system with biofiltration. The longer fish are held, the more weight they lose and the more stressed they become, so process fish as quickly as possible. ### Should I grade fish before or after transport? Grade before transport if you are shipping fish to different markets or if the transport tanks are sized by fish count. Grading at the farm allows you to load each transport tank with a uniform size class, which simplifies inventory and ensures that buyers receive the size they ordered. If you are delivering all fish to a single buyer, you can grade at the processing plant. ## Related Farming Guides This section will be populated with links to related farming guides on this site. Check back for additional resources on pond management, fish health, water quality, and aquaculture production systems. ## 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 - FAO Fisheries and Aquaculture: https://www.fao.org/fishery/en - USDA Aquaculture: https://www.usda.gov/topics/farming/aquaculture - WOAH Aquatic Animal Health Code: https://www.woah.org/en/what-we-do/standards/codes-and-manuals/aquatic-code-online-access/ - FAO Animal Production and Health: https://www.fao.org/animal-production/en/ - WOAH (World Organisation for Animal Health): https://www.woah.org/en/home/ > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.