Laura Tiu

The Effects of Size Grading on Production Efficiency and Growth Performance of Yellow Perch in Earthen Ponds

Abstract The culture of yellow perch Perca flavescens has received considerable interest in the Midwest and elsewhere in the USA as a result of the decline of wild populations and their high market demand. In this study, the effects of size-grading on the production efficiency and growth performance of food-sized yellow perch were determined in six 0.1-ha ponds by grading fingerlings into three size-groups (mean initial size): small (5.3 g), large (18.3 g), and unsorted (11.3 g). The mean percentage of marketable production from large-group ponds was significantly greater than that from the small- and ungraded-group ponds. The final biomass of large size-groups was 77% and 27% greater than that of small and ungraded groups, respectively, although no significant differences in total production were detected among the three size-groups. Size-sorting of fingerling yellow perch did not result in improved growth of the small-fish group. No significant differences in growth rates among the three groups were det...

Characterization of antibiotic resistance in commensal bacteria from an aquaculture ecosystem

The objective of the study was to improve the understanding of antibiotic resistance (AR) ecology through characterization of antibiotic-resistant commensal isolates associated with an aquaculture production system. A total of 4767 isolates non-susceptible to sulfamethoxazole/trimethoprim (Sul/Tri), tetracycline (Tet), erythromycin (Erm), or cefotaxime (Ctx), originated from fish, feed, and environmental samples of an aquaculture farm with no known history of antibiotic applications were examined. Close to 80% of the isolates exhibited multi-drug resistance in media containing the corresponding antibiotics, and representative AR genes were detected in various isolates by PCR, with feed isolates had the highest positive rate detected. Identified AR gene carriers involved 18 bacterial genera. Selected AR genes led to acquired resistance in other bacteria by transformation. The AR traits in many isolates were stable in the absence of selective pressure. AR-rich feed and possibly environmental factors may contribute to AR in the aquaculture ecosystem. For minimum inhibitory concentration test, brain heart infusion medium was found more suitable for majority of the bacteria examined than cation-adjusted Mueller Hinton broth, with latter being the recommended medium for clinical isolates by standard protocol. The data indicated a need to update the methodology due to genetic diversity of microbiota for better understanding of the AR ecology.

Effect of Stocking Density on Growth, Yield, and Costs of Producing Rainbow Trout, Oncorhynchus mykiss, in Cages

Abstract Rainbow trout, Oncorhynchus mykiss, were raised in culture cages (1 m3) to determine the effect of stocking density on growth, survival, and percentage of market-size fish. Large fingerling rainbow trout (20-25 cm, 232 g average weight) were stocked into six cages located in a 0.4-ha pond. Two stocking densities (100 or 200 fish/cage) were used, and fish were grown for 140 days (2000-April 2001). Average total harvest weight (35.0 kg) in the low-density cages was approximately one-half the average total harvest weight (61.2 kg) in the high-density cages. Average weight gain (11.7 kg to 15.1 kg) and feed conversion (1.2 to 1.5) were also smaller for the low-density cages. Average survival was 96.7% for the low-density cages and 94.2% for the high-density cages, with the percentage of market-size fish (< 29 cm) averaging 50.3% and 52.0%, respectively. Production costs for the actual experiment and the revenues from fish sold at the end of the study were collected. An enterprise budget based on the experimental results for the two densities was developed to determine if a culture operation of this size would produce a net return. Production costs and revenues from the experiment resulted in a large negative return (-

Establishment of mostly male groups of bluegills by grading selection and evaluation of their growth performance.

3,124) and high breakeven price (

No sex-specific markers detected in bluegill sunfish Lepomis macrochirus by AFLP

13.53/kg).

Effects of estradiol-17β on survival, growth performance, sex reversal and gonadal structure of bluegill sunfish Lepomis macrochirus

Abstract Concerns over the economic feasibility of commercial aquaculture production of bluegills Lepomis macrochirus have heightened the need for strategies to enhance growth. Recent studies have shown that individually reared bluegill males can grow twice as fast as females; such studies have generated increased interest in development of mostly male or all-male populations. In this study, we developed a practical procedure to establish mostly male bluegill groups through grading selection and we tested their growth against that of a normal population. A single cohort of bluegill juveniles was cultured in a pond for 1 year; when the fish reached a mean weight of 30.1 g, the cohort was graded and divided into two mostly male groups (top 25% and top 50% of fish by total length) and a mixed-sex control group. The percentage of males in each group was as follows: 50.0% in the mixed control group, 75.4% in the top 25% group, and 69.7% in the top 50% group. Weight gain per fish in the top 25% group was signif...

Gonadal sex differentiation in the bluegill sunfish Lepomis macrochirus and its relation to fish size and age

The amplified fragment-length polymorphism (AFLP) technique was used to identify sex-specific markers in bluegill sunfish. A total of 12 835 loci were produced by 256 primer combinations, of which nine (0.73 per thousand) exhibited presumed sex-associated amplifications in the pooled samples; however, none of which revealed sex specificity upon individual evaluation.