There is a variety of harvesting equipment used in the commercial fish farming industry. Various nets are available for harvesting, in addition to specialized equipment that includes livecars, boom trucks, loading baskets, fish pumps, boat with outboard motor, and other items.
The choice of equipment depends on the size of the operation, available labor, frequency of use, available capital, preferred harvest method, volume and sizes of fish harvested, and species considerations.
Cast nets:
These are inexpensive and useful for sampling. Cast nets are made of monofilament nylon, and the mesh size should be matched to the species harvested. Fish with spines entangle easily. With practice and patience, anybody can throw a cast net properly.
Lift nets:
Bait minnow and tropical fish producers may use lift nets to capture small numbers of fish. These nets are made of soft, small mesh that minimizes injury. Fish are lured into the trapping area with feed, and the net is lifted quickly when fish are evident. The lift net and its assembly are portable.
Short seines:
Short 10- to 20-foot long “Commonsense” minnow seines work well to harvest fry in tight schools. Seines can be pulled manually by two persons or can be shortened and used like a dip net from a boat. The water should be clear. Once fry break out of schools and scatter, a V-trap can be used for harvest of small, delicate fry.
Success depends upon knowing the habits of fish and locating the trap properly. The V-trap usually has glass or fine mesh sides that form a narrow vertical opening that fish enter. A lead panel may extend from one or both sides of the mouth to guide fish into the opening as they move along the pond bank. Set the trap so fry swim between it and the shore.
The lead panel intercepts fry and leads them into the trap. Use a dip net to harvest fish daily (or as often as necessary depending upon species) from the box shaped trap.
Gill nets:
These can be used in ponds to harvest large fish selectively or a few at a time. They are normally strung across a pond. They are made of clear, monofilament nylon that makes them difficult for fish to detect. Floats are used to mark their location, and each end is anchored. Nets can be totally submerged or extended from the surface to the pond bottom.
Fish can be driven into the net by a boat to increase the catch. Gill nets work best at night when less visible, and should be checked frequently because fish caught usually die. They can also be eaten or damaged by turtles or other predators.
Large seines:
The most common type of harvesting equipment is the seine or harvesting net. Seines work well in large regular-shaped ponds with relatively flat, unobstructed bottoms. Ponds that can be harvested without draining are called seine-through ponds. No water is drained for seining typical levee type ponds, but in some embankment ponds water levels are lowered to facilitate harvest.
Net features:
Mesh size. Select the proper mesh size to harvest fish of the desired size. Fish shouldn’t go through, be gilled or become entangled in the net. Raschel nylon mesh is available in various sizes and is recommended for fingerlings 4 inches or smaller.
Small mesh seines are harder to pull because of more resistance. Also, mud does not sift through them as readily. Seine length should be one and one-half times the widest part of the pond. This assures enough length to keep the weighted line on the pond bottom and levee toe as the seine is pulled.
The depth of the seine should also be one and one-half times the maximum water depth. For large commercial catfish ponds, seines may be longer than 1,000 feet. Because of such weight, tractors are used to pull them.
Texture:
Net texture is determined by the material and how the mesh is formed, either with knots or woven. Nylon nets should be coated with a resin or asphalt based net preservative to prevent catfish from getting caught by their spines. Polyethylene nets require no coating treatment.
Knotted net is suitable for catfish, but most scaled fish require soft, uncoated knotless nets. These nets limit injuries from scale loss caused by abrasions. Carp or buffalo fish, however, can be harvested with knotted nets.
Number 42 nylon twine is recommended for catfish and other large fish to provide adequate strength. Net manufacturers can recommend the proper size, number and distance interval between floats.
Bottom line:
The bottom line, or mudline, of the seine can have a many-ends sisal mudline, 2-inch diameter mudline of knotless mesh nylon netting or hard rubber rollers. The design affects how deep the bottom line digs into the pond bottom and its ease of pulling.
Evaluation studies of various mudline designs indicate that roller- mudline equipped seines are preferred when harvesting food sized channel catfish from ponds with irregular bottoms consisting of deep, soft muds.
The meshmudline is recommended when harvesting channel catfish from ponds with hard bottoms or harvesting fingerlings because of its lighter weight and tendency to clear mud.
Seine reels:
A hydraulically operated seine reel is often used to transport, store and beach the seine. There are various models and sizes. Most are single reels, but some have two. The smaller second reel hauls in the loose end of the seine when fish are funneled into a sock or livecar.
With the single reel, the loose end is landed manually. A standard 5-foot reel can store seines as long as 1,200 feet. The reel is mounted on a trailer. Some have hydraulic controls that pivot the reel into various positions to line up with the seine as it is landed.
Authors:
Gary L. Jensen and Martin W. Brunson
