Chapter 11: Harvesting and Handling
A major distinction between a hatchery and many other forms of aquaculture is that a hatchery’s goal to produce a live healthy product. When fish are produced for consumption they need only to remain alive a limited time after harvest but in a hatchery the fish must be harvested and handled in a manner so they will remain alive and healthy for an extended period of time. A successful harvest requires advanced preparation and scheduling. The recipients of the harvest must be notified and be prepared to receive the fish, holding facilities at the hatchery must be available, and a distribution schedule prepared. The method of harvesting is an important management decision that must be made well in advance of the harvesting season when fish are to be produced in ponds. Methods of harvesting ordinarily used are seining (pond full or nearly so), trapping, draining, or a combination of these.
Seining is the method of choice when the number of fish needed is relatively small or when ponds cannot be drained, and the fish are large enough to be handled safely. Seining is used to reduce the standing crop in a pond when the standing crop is too great to be safely harvested by draining the entire quantity of fish into a catch basin for harvest. Seining of a full pond can be efficient for larger fish that tolerate handling and can be concentrated in a small area in response to being offered a formulated feed or are a species that moves in a compact school.
Primary nursery ponds are usually not harvested by seining until the pond water level is lowered and the fish concentrated in the catch basin. At harvest the standing crop in a primary nursery pond is not too high, and the fish may be too delicate to be seined. A seine can be used in a primary nursery pond to crowd the fish, allowing the fish to be scooped up in water for transfer to a transport tank.
Some fish species are more easily seined than others. Fast swimming or bottom dwelling species often cannot be harvested efficiently by seining. Larger ponds become increasingly difficult to harvest. Considerable manpower or a mechanical seine puller is required for large ponds. Ponds with notable amounts of filamentous algae and rooted weeds can be very difficult to seine. Appropriate vegetation control should be applied far enough in advance to eliminate such weeds and allow water quality to return to normal before the start of the harvest. Seining is stressful to the fish, particularly when water temperature is high. Seining is not sufficient to completely harvest most ponds, and at some point the pond mush be drained.