Production Phases and Systems
Maintaining brood stock
Hatcheries used to produce catfish fry are simple facilities that use flow-through tanks for egg incubation and fry rearing. Egg hatching tanks are equipped with a series of paddles that gently rotate through the water to provide water circulation and aeration to the eggs. Incubation time varies from 5 to 8 days, depending upon water temperature.
At hatching, the fry (called sac-fry at this point) school in tight groups within the tanks and are transferred to a fry rearing tank. Initially, sac-fry are not fed because they derive nourishment from the attached yolk sac. Over a 3- to 5-day period after hatching, they absorb the yolk sac and turn black. At that time fry (now called swim-up fry) swim to the water surface seeking food. Fry are fed nutritionally complete feed for 2 to 7 days before they are transferred to a nursery pond.
The choice of a stocking rate is a compromise between the benefits of producing large fingerlings for foodfish growout and the economics of producing more small fingerlings in less space. Fish are fed a manufactured feed and grown to fingerling size (3 to 8 inches long) over a 5 to 10 month period. Fish are either allowed to continue growing in their original nursery ponds or are harvested and transferred to other ponds for growout to stocker-sized fish (0.1 to 0.25 pounds) or to food-sized fish (1 to 2 pounds).
Survival of catfish fry to fingerlings varies greatly from pond to pond, depending on the initial condition of the nursery pond, losses to bird predation, and the incidence of infectious diseases. Average survival from fry stocking to fingerling harvest in excess of 60 percent across all ponds on the farm is considered to be very good.
The three fundamental production variables in foodfish growout are cropping system, stocking rate, and size of fingerlings to stock. Farmers use various combinations of these variables, and it is impossible to describe a typical management scheme for production of food-sized channel catfish. Farmers have developed and used various production schemes based on experience, personal preference, and perceived productivity and profitability.
Cropping system refers to the stocking-harvest-restocking schedule. In the single-batch system, the goal is to have only one year-class of fish in the pond at a given time. Fingerlings are stocked, grown to the desired harvest size, and all fish are harvested before the pond is restocked with new fingerlings. In the multiple-batch system, several different year-classes of fish are present after the first year of production. Initially, a single cohort of fingerlings is stocked. The faster-growing individuals are selectively harvested ("topped") using a large-mesh seine, followed by addition ("under-stocking") of fingerlings to replace the fish that are removed plus any losses incurred during growout. The process of selective harvest and understocking continues for years without draining the pond.
Stocking rate is best defined as the maximum fish density (number per acre) over the production period. Under commercial conditions, stocking rate becomes an approximate goal rather than a precisely managed population variable because it is nearly impossible to know the true inventory of fish in large commercial ponds that are used for several years without draining. There is no consensus on the best stocking rate for commercial production, and rates used in the industry range from less than 3,000 fish/acre to more than 18,000 fish/acre.
The size of fingerling to stock is a critical factor in foodfish production, but very little systematic research has been conducted to determine the relationship between fingerling size at stocking and economic returns. Large fingerlings will reach foodfish size faster than small fingerlings, but large fingerlings are expensive because they require more time and space to produce. The best size fingerling to stock is therefore a compromise that depends on cropping system, fish stocking density, and fingerling availability.
Over 95% of the channel catfish produced in the United States are grown in ponds because this is the most profitable way to grow fish. The predominate type of ponds used are the traditional levee ponds typical of the Delta region of Mississippi and Arkansas and watershed ponds found in eastern Mississippi and western Alabama. Many farmers feel that intensifying fish production will reduce production costs. They are currently exploring two alternative production systems to do this: split-pond systems and smaller conventional earthen ponds with increased aeration rates.
Levee ponds are constructed on relatively flat land by taking soil from the bottom of the pond to serve as fill for levees. Ponds are typically rectangular and have a 2:1 to 3:1 ratio of length to width to minimize construction costs and to create shared levees between adjacent ponds. In recent years, the average size of newly constructed ponds has declined to 8 to 12 acres. As older, larger ponds (18 to 25 acres) have been renovated, producers have divided them into smaller production units. Where possible, ponds are built to contain an average of 5.5 to 6 feet of water depth. A bottom slope of 0.2 to 0.3 feet per 100 linear feet along the long axis of the pond creates adequate drainage.
Where groundwater is relatively abundant, wells are the preferred water source because groundwater is free of undesirable fish. Each pond should be capable of being drained independently. A perimeter drainage system should be constructed to receive effluents and to prevent water from standing outside levees.
Watershed ponds are constructed by building dams across valleys to form reservoirs. Watershed ponds are usually filled by surface runoff from an area above the dam. Some aquaculture facilities have large reservoirs that, in turn, fill smaller ponds with captured runoff. The amount and quality of water entering the pond from the surrounding watershed is dependent on several factors—slope, soil type, vegetative cover, and the amount of precipitation. Watershed ponds can be cheaper to build than levee ponds on flat land and they don’t require wells.
Since catfish ponds are seined for harvesting, pond bottoms must be smooth and almost flat. Watershed ponds need not be rectangular or square in shape. Irregular shorelines will work as long as the maximum width of the pond doesn’t exceed the length of the seines used for harvesting.
Split-ponds are constructed by dividing an existing traditional pond into two unequal sections with an earthen levee. The levee is breached by two sluiceways. A fish-holding section is about 15 to 20% of the total pond area and contains all the fish that would normally be grown in the whole pond. The waste-treatment section is about 80 to 85% of the total area and contains no fish. Water is circulated between the two sections using one of several pumping systems. During the day, water is pumped from the treatment section through the fish section to provide oxygen and remove waste products. At night, water exchange is stopped and dissolved oxygen is provided by mechanical aerators.
The original goal of the split pond system was to improve the ease of feeding, better inventory control, easier harvest, better aeration efficiency, improved health management, and protection from predators. It became evident that when stocked with hybrid catfish, loading rates and fish production were significantly greater in the split-pond than in traditional ponds. During nine years of study, annual fish production has ranged from 15,000 to 20,000 pounds per acre – 2 to 4 times more production than achieved in traditional ponds.
Intensively-aerated small ponds
A second approach farmers are using to intensify production is to stock catfish at high densities in smaller ponds (4 to 8 acres) and installing more aeration per acre. Aeration rates in these ponds range from 5 to 10 horsepower per acre, double or even triple rates found in traditional ponds only 10 years ago. Most commercial producers are stocking hybrid catfish into these intensive systems. Field observations and research trials reveal that these systems are capable of producing 12,000 to 18,000 pounds per acre.
MSU Publications & Information
Summary of Current Research on Catfish Fry Pond Management
Other Catfish Production Information
Channel Catfish Broodfish Management
Channel Catfish Broodfish and Hatchery Management
Design and Construction of Degassing Units for Catfish Hatcheries
Water Quantity and Quality Requirements for Channel Catfish Hatcheries
Managing Hatch Rate and Diseases in Catfish Eggs
Production of Hybrid Catfish
Site Selection of Levee-Type Fish Production Ponds
Construction of Levee-Type Ponds for Fish Production
Watershed Fish Production Ponds: Site Selection and Construction
SRAC Presentation: Advanced Aquaculture Systems – Split-ponds
Performance Evaluation of Four Different Methods for Circulating Water in Commercial-Scale, Split-Pond Aquaculture Systems
Oxygen and nitrogen dynamics in split ponds vs. conventional catfish production ponds
Performance Evaluation of Intensive, Pond-Based Culture Systems for Catfish Production in Mississippi: Year One