D.A. Davis

Sample Preparation Techniques for Determination of Fish Energy Density via Bomb Calorimetry: An Evaluation Using Largemouth Bass

Abstract We evaluated three homogenization and subsampling techniques for preparing fish tissue samples for bomb calorimetry to identify differences in efficiency for estimating fish energy density. We compared (1) drying the whole fish and homogenizing the dried fish tissue, (2) homogenization prior to drying and then drying the subsample of fish tissue, and (3) homogenization after autoclaving to soften the hard structures and then drying a subsample of the homogenized fish tissue. Sample drying time and energy density estimates were compared among techniques across a size range (wet mass = 32–1,080 g) of largemouth bass Micropterus salmoides. Both of the subsampling techniques reduced drying time by about 40% relative to drying the whole fish. All three methods provided statistically similar estimates of largemouth bass energy densities. The autoclave process was most efficient, minimizing both sample preparation time and drying time. Variance of energy density estimates was greater for both subsamplin...

Nursery Protocols for the Rearing of the Brown Shrimp, Farfantepenaeus aztecus: Effects of Stocking Density and Salinity

Abstract Recreational saltwater fishing in coastal areas of the United States of America is partly dependent on the availability of live bait for anglers. One bait species commonly used is the brown shrimp, Farfantepenaeus aztecus. Three experiments were conducted with eight-day-old post-larvae (PL8) to evaluate the effects of stocking density and water salinity on survival, growth, and feed conversion ratio (FCR) of F. aztecusin nurseries. In the first experiment, the effects of stocking density were evaluated for a period of 11 days. Post-larvae (PL) were stocked into round tanks (760 L) at densities of 30, 40, 50, and 60 PL/L with four replicates per treatment. There were no significant differences (P > 0.05) in final mean weight, survival, and estimated FCR among treatments. In the second experiment, shrimp were stocked into 159-L square polyethylene tanks at four densities (1.0, 1.9, 7.9, and 13 PL/L) and maintained for 12 days. Shrimp reared at low densities grew significantly larger and had significantly lower FCR than those stocked at higher densities. There were no significant differences in survival. In the third experiment, PL were stocked at two salinities (16 ppt and 32 ppt) with six replicates per salinity. Three of the tanks at each salinity were then treated with EDTA (3 ppm). Fourteen days after the start of the experiment, sub-samples of shrimp from each treatment were weighed and returned to the tanks. Salinity in the 32 ppt treatment was then gradually decreased to 16 ppt during a 24-hour period and the shrimp reared for an additional seven days. There were significant differences in mean weights among treatments at the end of the 14 day grow-out period (32 ppt, 10.1 mg; 16 ppt, 7.2 mg). At the end of the experiment, the use of EDTA did not seem to have an effect on production. However, shrimp subjected to late acclimation to the lower salinity were significantly smaller than those acclimated at stocking (11.8 mg vs. 21.2 mg). This reduced weight is presumably due to acclimation stress resulting in a lag in growth. The high salinity treatment resulted in significantly higher survival (32 ppt, 51.3%; 16 ppt, 44.4%), while the FCR was significantly lower (32 ppt, 1.75; 16 ppt, 2.08). Present results indicate that nursery systems, if properly utilized and correctly managed, could assist in the development of a viable bait-shrimp aquaculture industry.