Technology to Improve Louisiana Aquaculture

Louisiana supports one of the most diverse aquaculture industries in the nation. Research that can solve problems and create new or alternative opportunities is essential to the viability and progress of this industry. For catfish, research is needed to reduce feed cost and enhance growth rate and feed efficiency through improvements in reproduction, nutrition, genetics, and disease prevention. For crawfish, research is needed to improve the highly variable reproductive rates of female broodstock and to develop more effective trapping strategies and cold water baits to increase crawfish harvest during winter. Emerging aquatic species, such as hybrid striped bass and freshwater drum require unique approaches to prevent disease and increase production potential. Development of beneficial compounds from aquaculture processing wastes will not only reduce the environmental concern from these wastes but add value to the primary product. Finally, research to control Listeria monocytogenes is needed because it is a serious threat to many food processors and has been found in the environment of crawfish and fish processing plants. This project contains nine component research studies that will address current aquaculture needs and generate new knowledge to benefit producers, consumers, and the state's economy.
<p>
Catfish, crawfish, hybrid striped bass, and freshwater drum will be evaluated in replicated experiments to assess: the effects of graded levels of feed restriction and feeding frequency on catfish yield and production cost; broodstock conditioning, sperm cryopreservation, and artificial spawning of catfish brought into early reproductive condition by heating of small ponds, and fry production from natural spawning in the heated ponds; freshwater drum as an alternative for snail control to prevent infection by the trematode parasite Bolbophorus confusus in catfish ponds; the role of the Type III secretory system in the virulence of P. damelsae in hybrid striped bass; means for better assessment of crawfish reproductive success and development of management strategies to improve the probability of success; and continued refinement of crawfish trapping and baiting strategies with particular emphasis on new trap types and density combinations and on cold water baits. Food science-related projects will focus on adding value to both alligator and crawfish processing wastes by isolating collagen, elastin, and proteoglycans from alligator cartilage and determining their potential health benefits and by obtaining chitosan from crawfish shell waste and evaluating its effects on catfish off-flavor and shelf life extension. A food safety related study will investigate the use of copper metals and copper sulfate in coatings used to seal concrete to control Listeria monocytogenes in crawfish and fish processing plants.
<p>
2004/01 TO 2004/12<br>
Crawfish females collected in June and July from ponds where feed was provided exhibited a 14 percent increase in survival within artificial burrows and a 43 percent increase in spawning. Crawfish collected from natural burrows had a 133 percent higher incidence of spawning than females collected from traps. Crawfish yield with 3/4 inch square-mesh traps and 7/8 inch square-mesh traps did not significantly differ from 3/4 inch hex-mesh traps. An experimental molasses based bait was not effective in attracting crawfish compared to a commercially formulated bait. No significant differences in production yield of pond-raised channel catfish was observed between fish fed to satiation daily for 158 d (control) and fish subjected to iterations of 5 d of fasting followed by 14 d of satiation feeding (112 total feed days). Iterations of 10 d of fasting followed by 14 d of satiation feeding (97 total feed days) tended to produce lower numbers of marketable fish. A lower overall feed cost resulted. The potential for snail control in warmwater fish ponds using freshwater drum was evaluated from November through May in 20 outdoor tanks seeded with 20 adult planorbid snails each. Young of the year freshwater drum were stocked at two densities and two sizes. At the end of May overall drum survival was approximately 84 percent. No significant differences were apparent in snail control between density or size groups. Presence of drum significantly reduced snail populations. The effect of temperature (4, 25, and 37 degrees C) on the antimicrobial activity of copper and brass metals against L. monocytogenes counts were determined at day 0, 2, 4, 6, or 8. Results showed that at 4 degrees C, L. monocytogenes counts on the surface of brass were significantly reduced by 3 Log from day 2 to 8 as compared to the controls and on copper, counts were reduced to non detectable levels by day 8. At 25 degrees C, L. monocytogenes counts had a 6 Log reduction by day 6 when grown on the surface of copper and brass. At 37 degrees C, L. monocytogenes counts on the surface of the copper or brass were reduced to non detectable levels at day 8. A proteoglycan was extracted from alligator cartilage using MgCl2 and ethanol precipitation. SDS PAGE and MALDI TOF MS analyses have indicated molecular mass between 51.7 - 58 kilodaltons. Work is in progress to characterize the proteoglycan before carrying biochemical assays against enzymes associated with tumor angiogenesis. Work is proceeding to produce isogenic mutants of P. damselae subsp. Piscicida that carry mutations in selected orfs of the TTSS, to evaluate the mutant strains for cytotoxicity in cell culture, and to evaluate the ability of the mutant strains to survive in hybrid striped bass in competition with the wild type strain as a measure of attenuation. Spectrophotometry was used to determine sperm concentrations in channel and blue catfish. The most accurate absorbance readings for channel catfish occurred at 500 nm, but at 600 nm for blue catfish. Three different sperm concentrations were used for fertilization during artificial spawning and these yielded significant differences in fertilization.
<p>
IMPACT: 2004/01 TO 2004/12<br>
Short-term, late-season supplemental feeding programs may be justified if increased crawfish broodstock survival and reproduction predictably occur. Crawfish ponds should not be drained immediately after stocking trap-harvested broodstock. New trap construction materials, designs and baits are being evaluated that have significant potential to decrease harvest costs, and increase yield and profitability. Feed cost is approximately half of production cost in most fish farming operations. Repetitive periods of 5 days of fasting followed by 14 days of satiation feeding of channel catfish resulted in a lower feed cost and equivalent fish yield suggesting a possible economic advantage for this feeding regimen. Freshwater drum may serve as a management tool for snail control in polyculture with channel catfish to prevent loss from the trematode parasite Bolbophorus confuses. With the recurring recalls of ready to eat fish and seafood products due to contamination by L. monocytogenes there is a clear need to develop additional methods to prevent economic loss and possible deaths that can occur from foodborne listeriosis infections. Copper or brass metals could possibly be used to control L. Monocytogenes in hard to clean areas such as the drains or air vents of food processing environment. Spectrophotometric assays can be used to estimate sperm concentrations of catfish and there is a correlation between sperm concentration and fertilization.