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INVESTIGATOR: McClain, W. R.

PERFORMING INSTITUTION:
RICE RESEARCH STATION
LOUISIANA STATE UNIVERSITY
BATON ROUGE, LOUISIANA 70893

EVALUATION OF SELECTED ENVIRONMENTAL AND CULTURAL FACTORS AFFECTING CRAWFISH AQUACULTURE PRODUCTION

OBJECTIVES: 1.Determine the impact of selected environmental factors (e.g., rainfall patterns, soil type) on crawfish broodstock survival and reproduction while occupying burrows during summer. 2.Determine effects of crawfish stocking date (within April - July time frame) on survival to burrowing, survival within the burrow, and percentage to reproduce. 3.Investigate the effects of selected rice pesticides on crawfish survival, growth, and reproduction under varying conditions of exposure associated with rice/crawfish rotational practices. 4.Evaluate alternative harvesting and baiting strategies for increasing crawfish yields and sizes and increasing harvesting efficiency with respect to specific management practices for culturing crawfish.

APPROACH: Both laboratory and field experiments will be utilized to accomplish the stated objectives. Laboratory experiments will be conducted either in an environmentally controlled wet lab equipped with artificial burrows, culture tanks, and aquaria or in a covered outdoor tank, equipped with artificial burrows that closely simulate natural burrow environments. Culture tanks (38-L with bottom surface area of 0.085 m2) in the wet lab are equipped with supplemental aeration and flow-through or static water capabilities. When supplied with soil, established vegetation (e.g., rice), and pond water and stocked with crawfish, they will be used as micro-habitats that simulate pond culture environments. Aquaria and smaller individualized containers will be used primarily for bioassay assessments. Field studies will be conducted primarily at the south unit of the Rice Research Station (RRS), Crowley, LA, and will utilize approximately 22 small ponds (0.2 ha) managed to simulate commercial crawfish ponds typical to that region of Louisiana. The ponds are designed as rice-field-type crawfish ponds with individual water inlets and outlets. Other experimental units will consist of open-bottom cylindrical enclosures randomly placed in ponds or positioned adjacent to levees to act as mesocosms that contain most of the amenities of the open pond environment. These mesocosms (0.5 m2 bottom area) will provide replicated units in ponds where crawfish can be confined while exposed to pond environments.

NON-TECHNICAL SUMMARY: Production of crawfish in Louisiana is highly variable among geographical locations and from year to year. Unpredictable harvests make it difficult for producers to invest the necessary funds for operating and capital improvement. This project will attempt to establish a better understanding of the impacts of drought on survival and reproductive success of crawfish while occupying burrows, especially as relates to soil type and rainfall patterns. The impacts of rice pesticides and various stocking and harvesting practices on crawfish yields will also be evaluated.

PROGRESS: 2002/01 TO 2002/12
A series of baiting studies was conducted in replicated crawfish ponds. Three bait formulations were compared with fresh fish in a cool-weather (6 - 18 C water temperature) test. Compared with fresh fish, crawfish catch with the best formula was 74% lower using a 24-h bait set and 59% lower with a 48-h set. In a 9-week study under warmer temperatures, baiting with residual pieces of a stable formulated bait, even after 3 days of use in traps, proved as effective as fresh bait daily. Varying bait brands (or formulations) each day per week over the same 9-week period did not result in increased weekly catches when compared with consecutive use of the same bait; however, two of the bait brands used in the rotation were inferior, averaging 15% less in daily catch than the control. Impact of simulated drought on crawfish reproduction in burrows was also investigated. Simulated water table had little effect, but percentage of crawfish to reproduce was impaired 39% by restricted precipitation; providing corroborating support for antidotal observations regarding drought and reduced crawfish production. Water use budgets in experimental crawfish ponds were determined for a third consecutive year: 2.3 acre-ft of rainfall fell and 5.1 acre-ft of additional ground water were required for normal operations. Intentional discharge consisted of 1.1 acre-ft for management of dissolved oxygen and draw-down, while 0.7 acre-ft of non-intentional discharge was estimated for rainfall overflow and seepage. The reproduction rate of female broodstock collected from different culture environments was assessed in a lab study using artificial burrows. The percentage of red swamp crawfish to spawn was 31% for those collected from the capture fishery of the Atchafalaya Basin compared with 22% for pond-reared crawfish. Continuing research further evaluated aspects of the rice insecticide fipronil on crawfish. Results indicated that survival and growth of hatchling crawfish were significantly reduced when they were exposed to simulated culture conditions 21 weeks after Icon-treated seed was water-seeded in micro-habitats at 0.05 lb ai/A. In another study, fipronil levels in lab simulated rice-field tailwater following water-seeding (0.0375 lb ai/A) ranged from 9.8 to 13.8 ppb after 24 hours and resulted in significant crawfish mortality with little differences due to turbidity in the absence of sunlight.

IMPACT: 2002/01 TO 2002/12
Crawfish harvesting and broodstock reproduction results will likely have a direct impact for crawfish producers who are diligent and precise in their management strategy. Data generated from the simulated drought study further corroborate previous research and anecdotal evidence regarding drought and crawfish production and provide producers and researchers with a better understanding of cause/effect relationships. Information generated as a result of work with the rice pesticide Icon and with water use budgets provides producers and regulators pertinent information necessary for understanding impacts to production and the environment.

PUBLICATIONS: 2002/01 TO 2002/12
1. McClain, W.R. 2002. Some factors that influence crayfish mortality during purging and potential management strategies to mitigate death loss. Freshwater Crayfish 13:146-154.
2. McClain, W.R., Romaire, R.P., Linscombe, S.D., and J.J. Sonnier. 2002. Aquaculture Research. Ann. Res. Rpt., Rice Res. Stn., La. Agri. Exp. Stn., L.S.U. Agricultural Center, 93:272-299.
3. McClain, W.R. and R.P. Romaire. 2002. Effects of simulated drought on crawfish survival and reproduction in artificial burrows: a preliminary study. Programme and Abstract Proceedings, 14th International Symposium of Astacology, Queretaro, Mexico. August 2002. p. 43. (Abstract)

PROJECT CONTACT:

Name: McClain, W. R.
Phone: 337-788-7531
Fax: 337-788-7553
Email: rmcclain@agctr.lsu.edu