Besides food-sized and fingerling fish, there are situations when eggs and fry require harvesting. Catfish egg masses are usually removed from spawning boxes and transported to hatcheries for incubation.
To remove the eggs, use a wide blade scraper or putty knife to loosen the adhesive egg mass from the bottom of the spawning container. Gently raise the box toward the shallowest water along the bank so the eggs can be more easily retrieved if they fall out of the box.
Remove the eggs with your hand, and put them into a plastic fish basket that has mesh openings. The basket can be placed inside an inner tube for flotation. The openings allow water to pass freely through the basket as it is pulled from box to box.
Tie a rope between the egg collection container and your belt or pants’ belt loop to pull the container as you walk to check spawning boxes, and keep your hands free. Tubs or ice chests can also be used, but they are less suitable.
Water can warm more quickly and water quality can deteriorate faster unless eggs are emptied frequently and the water is replenished. Do not hold eggs in stagnant water during collection for more than 15 minutes without aeration or adding fresh, clean water.
Make sure all pieces of the egg mass are removed from the spawning box so the male catfish can service another female, rather than care for a small fragment of eggs. Yolk-sac fry can be harvested from incubation troughs by siphoning with a 1/2 inch-diameter clear plastic hose.
Siphon fry into a dip net or strainer that is submerged in a bucket of clean water. The fry can now be quickly stocked into a rearing trough. To harvest older swim-up fry, use a fine mesh aquarium dip net to transfer them from the rearing trough to a bucket of clean water for stocking into a transport tank. Always move small fish in a cushion of water, and minimize their time out of water.
Harvesting situations and options:
There are three harvesting situations to consider:
- Partial harvesting exists where only part of the fish are removed.
- The pond may also be topped where larger market-size fish are selectively harvested from ponds with mixed fish sizes.
- Finally, the pond maybe clean cropped, where all fish are harvested.
The only reliable way to harvest all fish from a pond is to drain it completely. This involves a combination of draining and seining. Avoid using a seine in very shallow water because it stirs up the mud and causes low dissolved oxygen and high toxic gas conditions which can be extremely stressful to fish.
Shallow water can also warm quickly in hot weather. Seine trapping relies on feed to attract fish into a trapping area. A seine at least 200 feet long works well. Locate the seine parallel to the pond bank or across a corner about 50 feet from shore. A pull rope attached to each end is staked on the bank for easy retrieval.
The trapping area should have a firm bottom, be free of any debris and be less than 5 feet deep. Catfish and other species may be shy initially, but can be lured into the trapping area by feeding outside the open end of the corral seine and drawing them in with a trail of feed.
Use floating feed to observe feeding activity. Feed routinely at the time you intend to harvest. Do not alter your feeding activity on harvest day, except for using less feed. To harvest, simply pull the coiled seine ends to shore. Drag the seine carefully to shore to concentrate fish.
Have enough labor available to keep the bottom line on the pond bottom while dragging the seine to shore. Trapping success in the same area requires a 7-to 14- day recovery time before fish lose their shyness and the operation can be repeated.
Because of the importance of baiting with feeds, this method is more effective during warm weather when fish are feeding actively. Many catfish producers prefer to top their ponds by harvesting larger market-sized fish in a population of mixed fish sizes.
This method works best in seine through ponds that require no draining. The same pond may have fish harvested three or more times yearly. Fish are harvested when sufficient numbers reach market size.
This may be 1,500 or more pounds per acre in large 10- to 20-acre commercial ponds. Harvesting efficiency in seine-through ponds should be about 70 percent to 90 percent of the harvestable sized fish, depending on species, size, experience of harvesters, and the condition of the pond and harvesting equipment.
Catfish can create large craters in pond bottoms that can become extensive after continuous production of 4 or more years. These depressions probably reduce harvest rates. However, there is considerable controversy over how often a pond should be clean cropped and renovated to restore fish inventories and repair pond bottoms and levees, Other trapping methods include large lift nets and drop nets, but they are usually not as effective.
The lift net covers too small an area, and repeated use can reduce fish production. Catches with the drop net decrease considerably after the initial catch. In ponds used for fingerling production, especially when raising delicate fish species, harvesting kettles or basins are common features.
They are made of poured concrete and have several openings with vertical grooves for placement of wood tongue and groove boards to adjust water levels inside the basin. These areas are located in front of the drain structure, and their bottom is the same elevation as the bottom of the drainpipe.
A water supply pipe is often located near the basin to furnish fresh, oxygenated water as needed. Concrete steps from the basin to the levee top make it easier to carry tubs or buckets of fish and water. Before fish are concentrated, the basin should be cleaned with a broom or other device while the drain is open to remove any mud or sediment that can accumulate in the area.
The harvest basin is usually found inside the pond, but outside kettles also exist. Fish are usually dip netted from the basin and placed in buckets of fresh water. These structures are common in government hatchery ponds that frequently harvest small fingerlings of game fish species.
Removal from ponds:
When fish are moved from ponds, they are commonly lifted with a loading basket attached to a hydraulic boom. The fish are first crowded in a livecar or cutting seine. The boom can be mounted on a special truck.
A front-end loader or backhoe will also work well with a few modifications, including an extension pipe. The loading basket is designed so fish drop through a trap door with an easy, safe release. The basket can move 500 pounds or more per load.
Weights are determined with in-line, spring-loaded or electronic scales. The loading basket net should be treated with a coating if used for catfish. Do not overload the basket if fish will be restocked or hauled on a long trip. Make sure people are clear of the swinging basket as it moves and nobody is underneath it.
Another method of harvesting fish involves dip netting fish into buckets or tubs filled with clean water. Fish should be moved quickly and should not be overloaded. Water quality deteriorates rapidly when fish are concentrated, especially in warm weather.
A bucket-brigade helps reduce the strain and work of heavy lifting. Remember, one gallon of water weighs 8.35 pounds! This method works well for small, delicate fish where special harvesting precautions are required, but it can be time consuming if many fish are harvested.
Seine maintenance:
Seine storage and care are important to prolong the life of equipment. Uncoated nylon seines are damaged by direct sunlight. Remove dead fish that can attract rats, which damage seines. Short seines should be hung in a covered site and air-dried.
Never store a damp and unclean seine in a heap. Some aquatic weeds, parasites and infectious diseases may be transferred from pond to pond by harvesting equipment. For this reason, remove any fish or nuisance aquatic weed fragments. Air drying the seine can kill most parasites.
Diseases such as bacterial ESC may remain alive in moist mud balls not cleaned from seines. Repair any holes in the seine as soon as they are detected in order to maintain the equipment in workable condition and ready for use.
Summary:
Fish harvesting is an important step in getting fish out of production facilities in good condition so their survival and quality for other uses are assured. Experience and common sense will be valuable factors to assure success.
Take time to plan properly before putting nets into the water. Do not forget that fish are sensitive to handling, and that harvesting is the first stress of more to come if fish will be graded, held, transported and restocked.
It takes a higher quality fish to live after harvesting compared to one that will shortly be processed.
Authors:
Gary L. Jensen and Martin W. Brunson
