Aquaculture is an established and viable commercial agricultural practice in many states. It includes a variety of native and exotic species grown for human consumption, fish bait, recreational fishing and hobby use.
At some time in the production cycle from brood fish to marketing different live product forms, one or more life stages of fish must be harvested from the culture facility.
A successful fish farmer must know how to keep fish alive and healthy when they are moved. Different handling operations, like harvesting, can trigger stress-related conditions in fish.
Stress from various handling practices weakens fish and makes them more susceptible to disease outbreaks and adverse physiological imbalances.
The sensitivity of fish to stress associated with handling varies among species. Some are hardy, while others are extremely delicate and sensitive to the smallest of stressors.
Eggs and young fish are more susceptible to sudden changes in their environment than are older, larger fish. More care and precautions are required during harvesting if fish will be restocked into other facilities for further growout rather than sent to a nearby processing plant.
However, recent problems in the catfish industry with red spots and blotches in fillets, called “red spot syndrome,” are thought to be caused by stress incurred during harvest and transport to processing facilities.
Therefore, it is wise to take every stress prevention measure possible any time fish are handled or harvested, regardless of their destination. Several methods can be used to harvest fish efficiently and safely, but careful planning is required for a successful harvesting operation.
Too often, ponds are seined and only a few fish are caught be cause of improper harvesting techniques, poor pond design or insufficient planning. Consequently, harvesting logistics should always be considered in the design and construction of aquaculture ponds.
The approximate number and weight ranges of fish in ponds should also be known or projected so both the pond owner and buying customer are not disappointed with a shortage of fish for delivery.
Pre-harvesting guidelines:
Plan easy removal. Before plan ning the harvest operation, make sure that fish can be removed easily from the production unit. If a cage or raceway is used to growout fish, then harvesting is some what simplified and fish numbers and weights should be known.
However, when fish are in a large pond, several factors can delay or stop harvesting. Also, an inventory of fish stocks is more difficult to maintain when a pond has been in continuous production for several years. In such systems, larger fish are “topped” and smaller fish have been understocked, resulting in a wide diversity of sizes of fish in the pond.
Avoid debris and delays:
First, check for debris on the pond bottom that will snag the seine or livecar. Aquatic plants may not be visible at the water surface, but may be growing at or near the pond bottom. These plants can cause the net to roll up at the bottom and may make seine dragging impossible.
Fish can be killed if they are entrapped in aquatic weeds during harvest. Nuisance weeds should be controlled before harvesting is scheduled. During an unexpected delay in harvesting, fish prices may change, an off-flavor condition may develop, and the crop may have to be held into the next growing season, seriously impacting cash flows. So, avoid unnecessary delays that may be costly.
Take samples. It is important to know what’s in your pond before harvest. Sample fish with a short seine, cast net, lift net or snag hooks, depending on species. Keep records of fish numbers and amounts of feed consumed.
Ensure that the quantity of fish expected to be harvested can be marketed. Otherwise, you may have to release many fish after expending considerable time and labor. The harvesting operation may severely stress fish after they are trapped, crowded and held.
Release of these fish back into the pond or culture facility can markedly affect their mortality risk.
Check fish health:
It is essential that fish are healthy and in good condition before being harvested. Signs of good condition include good feeding appetites, no mortalities and no obvious external problems. A sample of fish can be examined by a qualified fish health specialist to determine if any obvious health-related problems exist.
This does not mean that fish are certified to be disease free, but it does provide more information to determine the condition of fish stocks. If sick fish are handled, the added stress can trigger a disease outbreak that can cause high mortalities.
Try to pick favorable conditions:
You should have adequate labor, equipment and supplies available for harvesting. Weather and water quality conditions may also be important. On many farms, food sized fish for processors are harvested regardless of the weather. Only thick ice on ponds may stop some harvesting operations.
Movement of large trucks and harvesting equipment can rut and damage levee tops that are excessively wet and lack protective cover such as gravel. In severe cases, equipment may not even be able to reach ponds because of the poor condition of access roads or levee tops. Main levees should have a gravel cover that provides an all-weather surface.
Stop feeding:
Take fish off feed before they are harvested. Withdrawal varies from one to two days during summer, to three or more days during winter. This is especially true if fish will be transported long distances.
Undigested food can be regurgitated in the transport tank and foul the water quality. Fish are also hardier and less stress occurs when their stomachs are empty. If food fish have been fed medicated feed, be sure that the proper withdrawal time has passed before they are harvested for processing.
A 21-day withdrawal period is required for Terramycin® medicated feeds and three days for feeds containing prescribed levels of Romet® for catfish. Water quality conditions should be good during harvest. Beware of possible low oxygen concentrations when fish are harvested at or shortly after sunrise.
Check for hydrogen sulfide:
In deep water ponds, hydrogen sulfide can accumulate in oxygen-deficient bottom muds and may be released upon disturbance of the pond bottom. This gas is highly toxic to fish and can be detected by a smell similiar to that of rotten eggs. If unsure about this condition, stir up the mud around the proposed harvesting site to determine if a potential problem exists.
If a rotten egg smell is noticed, find another suitable site. Stir up the site to release the gas before harvesting or treat with potassium permanganate to oxidize the gas. This condition is seldom a problem in shallow, warmwater fish ponds.
Check temperatures:
Harvest sensitive species during the early morning when water temperatures are lower and sunlight is less intense. Some fish, like golden shiners, striped bass and the striped bass hybrids, are harvested most successfully at water temperature less than 65°F to minimize stress and fish losses. They require special handling during harvest at higher temperatures.
Fish should be moved quickly from ponds to buckets or transport tanks in freezing, windy weather. Exposure to sudden temperature changes can shock fish, especially small ones.
Investigate custom harvesting:
In some areas, harvesting can be contracted. The custom harvester supplies the labor, equipment and expertise. Cost is based on the total pounds of fish harvested and possibly a distance factor.
Producers may also cooperate in a local area by sharing labor and capital for harvesting purposes. Many farms have their own harvesting capability when harvesting is frequent or self-sufficiency is needed because of the unavailability of custom services. Purchase of specialized harvesting equipment should be cost beneficial, and adequate labor is essential.
Authors:
Gary L. Jensen and Martin W. Brunson
