Commercial catfish production

Production Process A typical production cycle for channel catfish farming begins with spawning of brood fish. Spawning begins in the spring when water temperatures increase to above 70º F. At that time, brood fish held in ponds randomly mate and the fertilized eggs are collected from spawning containers and moved to a hatchery. Eggs hatch after 5 to 8 days of incubation and fry are reared in the hatchery for an additional 4 to 10 days. Fry are then transferred to a nursery pond, fed daily through the summer, and harvested in autumn or winter as fingerlings. Fingerlings are then stocked into foodfish growout ponds, fed daily, and harvested when they reach 1 to 2 pounds. Roughly 18 to 36 months is required to produce a food-sized channel catfish from an egg. Foodfish are harvested year-around to meet the needs of processing plants, so ponds on a given farm usually contain fish at various stages of growout throughout the year. Maintaining Brood stock Channel catfish brood stock are easy to maintain in pond culture, and spawning efficiency is reasonably good without any special manipulation of environmental conditions or the need for hormone treatments. Although channel catfish may mature at 2 years, they must be at least 3 years old and weigh at least 3 pounds for reliable spawning. Fish 4 to 6 years old, weighing between 4 and 8 pounds are considered prime spawners. Older fish produce fewer eggs per body weight and larger fish may have difficulty entering the containers commonly used as nesting sites. Brood stock are maintained at relatively low standing crops (less than 2,000 pounds/acre) to provide good environmental conditions and minimize suppression of spawning by overcrowding. Brood fish are seined from ponds and inspected every year or two. Large fish, which may be poor spawners, are culled and replaced with smaller, younger brood fish. Periodic inspection of brood fish also provides an opportunity for adjusting the sex ratios within brood populations. Spawning activity will begin in the spring when water temperatures are consistently around 75º F. Spawning occurs over a period of several hours as several layers of adhesive eggs are deposited in spawning containers. Females between 4 and 8 pounds typically lay between 3,000 and 4,000 eggs per pound body weight. Spawning success (percentage of females spawning) ranges from 30 to 80 percent each year, and depends mainly on the condition and age of the female brood fish and water temperatures during the spawning season. Nesting containers are checked every 2 or 3 days for the presence of eggs. The eggs collected from the brood pond are placed in an insulated, aerated container and transported to the hatchery. Hatchery Phase Hatcheries used to produce catfish fry are simple facilities that use flow-through tanks holding about 90 to 100 gallons of water for egg incubation and fry rearing. The most critical factor for a successful hatchery is a dependable supply of high-quality water. Egg hatching tanks are equipped with a series of paddles spaced along the length of the tank to allow wire-mesh baskets to fit between them. One or two egg masses are placed in each basket and the paddles gently rotate through the water to provide water circulation and aeration. The incubation time varies from 5 to 8 days depending upon water temperature. At hatching, the fry (called sac-fry at this point) fall or swim through the wire-mesh basket and school in tight groups. Sac- fry are siphoned into a bucket and transferred to a fry rearing tank. Aeration in fry rearing tanks is provided by surface agitators or by air bubbled through airstones. 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. Swim-up fry must be fed 6 to 12 times a day for good survival and growth. Fry are fed nutritionally complete feed for 2 to 7 days before they are transferred to a nursery pond. Fingerling Production Culture practices for fingerling production are relatively standardized across the industry, especially when compared to the wide variety of production strategies used to grow food- sized catfish. Fry grow faster when stocked at lower densities but more space is required to grow larger fingerlings at lower densities. Stocking rate is therefore a compromise between 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 of 0.1 to 0.25 pounds or to food-sized fish of 1.2 to 2.5 pounds. It is important to fertilize nursery ponds so that they contain abundant natural foods to promote growth until the fry are large enough to switch to manufactured feeds. A finely ground feed should be offered once or twice daily to train fish to accept the feed. As the fish grow, feed particle size is increased. A month or so after stocking, the fish (now called fingerlings) are fed once or twice daily to satiation, using a small floating pellet with 32 to 35 percent crude protein. Because fingerling populations are particularly susceptible to infectious diseases, disease management takes on added importance in this stage of production. 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. Foodfish Production Cultural practices used for foodfish production differ from farm to farm, and the process of growing a food-sized catfish can take many paths after the fingerling phase. Most farmers divide fish stocks only once between the nursery phase and the foodfish growout phase. In this scheme, fingerlings are harvested and restocked into foodfish ponds at roughly one- tenth to one-twentieth the density of nursery ponds because fish will be ten to twenty times heavier when harvested as foodfish. This one-step production scheme is not as simple as it appears because there are many options for managing foodfish ponds. Another approach to producing food-sized fish is to divide twice between the nursery phase and foodfish growout. The first division produces a medium-sized fish called a "stocker". The second division is made when stockers are harvested and restocked for growout to food size. In this scheme, small fingerlings (2 to 3 inches) are stocked at about 40,000 to 60,000 fish/acre and grown over one season to produce stockers weighing 0.1 to over 0.3 pounds. The stockers are then harvested and moved to foodfish growout ponds. As with the one-step scheme described above, there are several options for foodfish growout using stocker-sized fish. 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 to initiate the next cropping cycle. 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. Whether ponds are operated as single-batch systems or multiple-batch systems, 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 500 fish/acre to more than 10,000 fish/acre. One explanation for the wide range of stocking rates used by catfish farmers is that production goals, facilities, and resources vary from farm to farm. 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. In addition, large fingerlings can be difficult to obtain because most fingerling producers prefer to stock fry at relatively high densities and move fingerlings to foodfish ponds as soon as possible to avoid risk of loss to infectious diseases and predacious birds. The best size fingerling to stock is therefore a compromise that depends on cropping system, fish stocking density, and fingerling availability.