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In order to evaluate utilization variation of, and growth response to, soybean meal diets in largemouth bass for breeding programs, test diets with 0%, 35%, and 50% fishmeal having been replaced by soybean meal (SBM; S0, S35, and S50) were administered to three northern strains of largemouth bass (LMB; Jones, Marlow, and Remlinger). In the S35 and S50 groups, the Marlow and Remlinger strains had much better growth response to soybean meal diet (SMD) than the Jones strain, indicating that these two strains can better utilize diets containing high level of SMD. The results suggest that genetic variation exists for growth and feed efficiency in LMB fed diets containing both SBM and fishmeal, and genetic improvement may be possible for the trait of feed efficiency. In all the three strains, the growth performance of individuals in the S35 and S50 groups declined when compared with the S0 group, and the specific growth rate and weight gain correlated negatively with dietary levels of SBM. Genes that were differentially expressed between dietary SBM levels were identified. Transcripts of genes related to insulin-signaling pathway and fatty acid metabolism and biosynthesis were significantly downregulated in the S35 and S50 groups compared with the S0 group. Interestingly, several transcripts of genes (egfr, pla2g4, and ugt) involved in GnRH-signaling pathway and steroid hormone biosynthesis were also downregulated in the S35 and S50 groups, inferring that feeding with SMD could impair the sexual development of juvenile LMB. Likewise, the genes related to insulin signaling and fatty acid metabolism and biosynthesis were downregulated in the Jones strain compared to the Marlow and Remlinger strains in all three treatments. Overall, the Marlow and Remlinger strains exhibited better adaptation to SBM diets, and could be considered as potential breeding candidates. These results also suggest that insulin-signaling pathway and fatty acid metabolism and biosynthesis play important roles in adaptation to diets with high levels of SBM in LMB. This study provides useful information for LMB breeding programs, and it contributes to our understanding of genetic mechanisms related to growth performance of LMB fed with high levels of SMB.

Much interest has been generated concerning the development of monosex male populations of bluegill Lepomis macrochirus due to their more rapid growth capacity relative to females. The methods involved to develop monosex population require a comprehensive understanding of the underlying basis of sex determination and gonadal function with the development of monosex male populations. In this study, effects of genotype by temperatures on sex determination, and sexual size dimorphism and growth were tested on two batches of fry from different geographic populations. In the first batch, sex ratios significantly deviated from 1:1 in 29 °C and 34 °C groups, in which a significantly higher proportion of males (70.64% and 66.67%) were found ( P P P > 0.05). The pooled sex ratios were compared and this showed that temperature had significant effects on sex ratios in the first batch of fish ( P P > 0.05). Through histological examination, intersex fish were identified in 17 °C and 34 °C groups. Rearing temperature strongly affected the growth of bluegill. Fish reared at the temperature of 29 °C performed best, followed by fish at 34 °C, 23 °C and 17 °C. No significant differences ( P > 0.05) were detected in the growth of juvenile bluegill (

Bluegill (Lepomis macrochirus) monosex culture holds considerable potential as a method to improve bluegill aquaculture production as males grow much faster than females. A detailed understanding of the time of gonadal development and differentiation is critical to control sex and optimize culture. In the present study, we systematically studied gonadal sex differentiation of the bluegill sunfish and its relation to fish size and age from hatching to 90 days post hatching (dph) using a slow-growing batch (SGB) and a fast-growing batch (FGB) of fish. The results indicated that the gonadal differentiation in bluegill was more related to body size than to age. In presumptive ovaries, germinal and somatic differentiation began between 13.2 and 16.0 mm (60 dph in SGB and 30 dph in FGB) in total length (TL). The outgrowths from the proximal and distal portions of the gonads and the fusion of the outgrowths to form the ovarian cavity occurred between 16.0 and 21.0 mm TL (80 dph in SGB and 50 dph in FGB) with germ cells undergoing meiosis. The gonads in the females larger than 25.5 mm TL always had peri-nucleolus oocytes. In presumptive testes, the efferent duct formed in the fish ranging from 25.4 to 28.0 mm TL (90 dph in SGB and 70 dph in FGB) with the onset of meiosis and testes contained spermatocytes exhibiting active meiosis in males larger than 33.0 mm TL. These findings indicate that bluegill is a differentiated gonochorist and sex differentiation occurs earlier in females than males. Based on our results, we suggest that the critical period of sex differentiation in bluegill occurs between 13.2 and 16.0 mm TL and histological sex differentiation is distinguishable in most fish larger than 21.0 mm TL.

We systematically investigated the feminization of bluegill Lepomis macrochirus by oral administration of various doses of estradiol-17β (E 2 ) and evaluated their effects on the growth performance, production and gonadal structure of sex-reversed female bluegill at both sex ratio and histological levels. With positive control treatment, 30-day-old fry were fed with E 2 at 50, 100, 150 and 200 mg kg − 1 diet for 60 days. The survival of fish in the E 2 treated and control groups was not significantly different ( P > 0.05). The growth of the treated fish was significantly retarded during the period of treatment, while there was no side effect detected post-treatment and the retarded fish caught up during 120 days of culture after E 2 treatment. All the treated groups produced 100% monosex female populations based on the macroscopic shape of gonads, and there were no significant differences detected between any E 2 treatment and control group in the mean GSI of females during the spawning season from June to October ( P > 0.05). Histologically, 13.3% and 5.0% of the intersex fish were determined to come from the 50 and 100 mg kg − 1 E 2 treatment groups, respectively, with 6.9% and 4.1% of the gonadal area containing spermatocytes. Most of genotypical male fish treated with exogenous E 2 developed gonadal structures histologically indistinguishable from the gonads of females. This study suggests that 150 mg kg − 1 E 2 is the optimal dosage for feminization in bluegill, with 50 and 100 mg kg − 1 E 2 being sub-optimal and 200 mg kg − 1 E 2 being over-optimal.

As a prelude to strain selection for domestication and future marker assisted selection, genetic variation revealed by microsatellite DNA was evaluated in yellow perch, Perca flavescens, from four wild North American populations collected in 2003-2004 (Maine, New York, North Carolina, and Pennsylvania,), and two captive populations (Michigan and Ohio). For the loci examined, levels of heterozygosity ranged from H-e=0.04 to 0.88, genetic differentiation was highly significant among all population pairs, and effective migration ranged from low (N(e)m=0.3) to high (N(e)m=4.5). Deviation from Hardy-Weinberg equilibrium was regularly observed indicating significant departures from random mating. Instantaneous measures of inbreeding within these populations ranged from near zero to moderate (median F=0.16) and overall inbreeding levels averaged F-IS=0.18. Estimates of genetic diversity, Phi(ST), and genetic distance were highest between Michigan and all other broodstock groups and lowest between New York and Ohio. Genetic differentiation among groups did not correlate with geographic distance. Overall, the patterns of variation exhibited by the captive (Michigan and Ohio) populations were similar to patterns exhibited by the other wild populations, indicating that spawning and management practices to date have not significantly reduced levels of genetic variation. (C) 2007 Elsevier B.V. All rights reserved.