C. R. “Chuck” Weirich
Although many advances have been made during the rapid growth of the catfish industry, today’s culture practices are about the same as those developed over 25 years ago. Also, most ponds used to grow catfish are larger than 10 surface acres. The use of outdated or unrefined culture practices coupled with large pond culture systems undoubtedly restrict potential fish yields. Commercial yields range from a modest 3,000 to 6,000 pounds per acre per year.
The goal of the catfish production research program at the Aquaculture Research Station
is to enhance all phases of production by developing new or refined culture practices. Catfish production cycle includes three phases
The catfish production cycle consists of three phases: hatchery, nursery pond and growout. During the hatchery phase, egg masses procured in the spring are transported to a hatchery where they are incubated. At hatching, fry possess a yolk for four to five days and are called “sac fry.” After yolk absorption, fry are called “swim up fry” because they swim to the surface in search of food. Swim up fry are typically held in the hatchery from two to 10 days and fed a finely ground feed before they are stocked into nursery ponds at rates up to 200,000 fry per acre. Fish are fed pelleted feeds and after 120 to 180 days are harvested and stocked into food fish production ponds at rates up to 10,000 fish per acre.
Food fish production ponds are managed using single-crop or multiple-crop systems. In single-crop systems, fish are reared until reaching a market size of 1 pound to 1.5 pounds, at which time ponds are harvested, drained and refilled, and restocked to begin another production cycle. In multiple-crop systems, ponds contain fish of varying size classes. Market-size fish are selectively harvested with annual restocking of fingerlings. Thus, multiple-crop systems are constantly in production and are rarely drained. The multiple- crop system is the most common production system used in Louisiana and other catfish-producing states. Fry and fingerling production
The following experiments have been or are being conducted to develop new and improved hatchery and nursery pond protocols to enhance production of fry and fingerlings. Effect of salinity on production of fry and fingerlings
. Although almost all catfish are produced in fresh water, several Louisiana producers have access to saline groundwater. Because little information on the effect of salinity on fry and fingerling production was available, studies were initiated in 1995. In the first study, egg masses were hatched and fry were reared for 10 days at salinities of 0, 1, 2 or 4 grams per liter. Results indicated that percent hatch of eggs and percent survival of fry were enhanced at a salinity of 1 gram per liter (Figure 1).
In the second study the effect of salinity on production of fingerling catfish was determined over two growing seasons (1997 and 1998). In each growth trial, fry were reared for 120 days at salinities of 0, 1, 2 or 4 grams per liter. Results revealed that while salinity had no effect on feed conversion and percent survival, weight and total yield were improved when fish were reared at a salinity of 1 gram per liter. Effect of age of fry at stocking on fingerling production.
Although most producers feed swim up fry for two to 10 days before stocking into nursery ponds, several hatcheries in Louisiana have begun to stock sac fry to reduce feed and labor costs. To investigate this practice, a study was initiated in 1998 in which fry were stocked at two, seven or 14 days after hatching and reared for 120 days. Results indicated that there was no difference in production characteristics between age groups, suggesting that sac fry can be stocked into nursery ponds without reducing production. This study is being repeated. Effect of hatchery diet on fry growth and fingerling production
. Although a considerable amount of work has been done to develop and refine diets and feeding practices for production of food fish, few nutritional studies have examined the hatchery and nursery pond phases of production. In 1997, two hatchery growth trials were conducted using four different hatchery diets: catfish starter alone or catfish starter supplemented with brine shrimp cysts at 25 percent, 50 percent and 75 percent of the total diet. Results from both trials indicated that weight of fry increased with increased levels of brine shrimp cysts. To investigate the effect of brine shrimp cyst supplementation of hatchery diets on fingerling production, fry from the second hatchery growth trial were reared for 120 days. Results revealed that fingerlings reared from fry fed hatchery diets supplemented with brine shrimp cysts at 50 percent and 75 percent of the total diet were larger and had a higher total yield than fish fed other hatchery diets (Figure 2). Enhancing production
The following experiments have been or are being conducted to develop new or improved culture practices to enhance production of food fish.
Effect of salinity on production of food fish in multiple-crop ponds.
A three-year study was begun in 1998 to evaluate the effect of salinity on production of food fish. Three salinity levels are being evaluated: 0, 1.5 and 3 grams per liter. Fingerlings are stocked each winter and food fish are harvested each spring and fall. Data are maintained on production characteristics and will be analyzed at the study’s conclusion. Results from the two harvests conducted thus far show that total yield of fish has been higher in ponds containing low levels of salinity, but differences at this time are not statistically significant.
In addition, a study is being conducted to determine the effect of salinity on selected blood parameters and health status of fish. Another study will evaluate the effect of salinity on phytoplankton, off-flavor compounds and off-flavor status of fish. Effect of temporarily sequestering fingerlings on production of multiple crop pond.
Although most production manuals recommend that fingerlings 6 inches or longer should be stocked for growout, most producers have access to fingerlings only 2 inches to 4 inches long. It seems reasonable to assume that smaller fingerlings would not only take longer to reach harvestable size, but also may be more prone to competition and cannibalism from larger fish in multiple crop ponds.
One way to increase production in multiple ponds stocked with small fingerlings may be to sequester fingerlings temporarily to allow additional growth before release. In 1997, a study was completed in which fingerlings were stocked into ponds containing equal numbers of larger fish. Ponds were open or contained cages for sequestration. Fingerlings were held for 120 days before being released. At the end of the growing season, ponds were harvested. Results indicated that although survival of fingerlings was not improved by sequestration, weight of both sizes of fish and total yield were higher for ponds which had contained cages. To investigate this topic further, a three-year study was initiated in 1998. C. R. “Chuck” Weirich, Assistant Professor, Aquaculture Research Station, LSU Agricultural Center, Baton Rouge, La.
(This article was published in the fall 1999 issue of Louisiana Agriculture.)