Establishment of Mostly Male Groups of Bluegills by Grading Selection and Evaluation of their Growth Performance

—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 significantly greater (P , 0.05) than that in the mixed group throughout most of the experiment. There were no significant differences detected in survival among the three groups, although the top 25% group had survival of 96.0% compared with 90.6% and 90.5% for the top 50% group and the mixed control group, respectively. The top 25% group had the highest percentage (46.3%) of fish reaching 150 g at the end of the experiment, followed by the top 50% group (28.3%), and the mixed control group (12.7%). The coefficient of variation (CV) for weight decreased in all three groups over time; the mostly male groups maintained lower initial and final CV values than did the mixed control group. Results indicate that mostly male bluegill groups are able to grow faster than typical mixed-sex populations, and social interaction costs among communally reared males did not significantly decrease growth of mostly male populations in the aquaculture settings. The bluegill Lepomis macrochirus and its F 1 hybrid (female green sunfish L. cyanellus 3 male bluegill) have long been commercially cultured to support recreational fishery stocking needs throughout the mid-southern and southeastern United States (Brunson and Robinette 1986; Tidwell and Webster 1993; Flickinger et al. 1999; Brunson and Morris 2000). In the north-central region of the country, effort has more recently been directed towards rearing lepomid sunfishes for food markets (Garling et al. 1992; Garling and Sheehan 1999; Wang et al. 2000; Hayward and Wang 2002, 2006). Whereas mostly smallto intermediate-sized sunfish have been reared for recreational stocking purposes, substantially larger fish (225–340 g) are desired for food markets (Brunson and Morris