ALBERT

Notes: We investigated the feminization of bluegill and black crappie by short periodic immersions in an aqueous estradiol-17β (E2) solution. Bluegill fry (13.8 mm) were immersed in a 1 mg L−1 E2 solution every 5 days on three occasions over an 11-day period. In the positive control treatment, the same cohort of fry was fed 200 mg kg−1 E2 diet for 45 days. Two different size (26.1 and 20.1 mm) but the same age (45 days old) black crappie fry were immersed in the same concentration of E2 solution for 5 h a day every 3–5 days on 10 occasions between 45 and 86 days post hatch. Both modes of E2 administration were effective to induce feminization in bluegill. Feeding fry E2 impregnated diet for 45 days yielded 99.3% female populations from a 38.8% female experimental population. Only three short-time E2 immersions of fry over a much shorter treatment period also produced 76.9% female populations. E2 immersions had no effect on sex ratios of larger black crappie fry and produced variable levels of feminization (60–82% female) in smaller black crappie fry. Results of the present study showed that feminization in both species can be achieved by periodic immersions of fry in a 1 mg L−1 E2 solution with no adverse effects on survival. Yet, further researches on timing and intensity of immersion treatments are still needed for optimization of the procedures.

Notes: To allow for the initial identification of practical diet formulations for red snapper culture, the present study was conducted to evaluate the effects of feeding varying levels of dietary protein and lipid on growth and body composition of juvenile and sub-adult red snapper. Twelve diets were formulated to contain varying levels of dietary protein and lipid. In trial 1, juvenile red snapper (initial mean weight 5.9 g) were offered diets with graded levels of dietary protein (32%, 36%, 40%, 44%) and practical energy to protein ratios. In trial 2, juvenile red snapper (initial mean weight 8.64 g) were offered isonitrogenous diets (44% protein) containing graded levels of dietary lipid (8%, 10%, 12%, 14%). Sub-adult fish (initial mean weight 151.5 g) were used in trial 3 and maintained on diets similar to those of trial 1 (32–44% protein). Sub-adult fish (initial mean weight 178.3 g) in trial 4 were offered isonitrogenous diets containing 32% dietary protein and graded levels of dietary lipid (6%, 8%, 10%, 12%). There were no significant differences in growth, feed efficiency ratio (FER) or survival in juvenile fish. Juvenile fish offered 32% dietary protein exhibited a significantly greater (P=0.0497) protein conversion efficiency (PCE) than fish offered a diet containing 44% dietary protein. Juvenile fish in trial 2 also had significantly higher (P=0.005) intraperitoneal fat ratios (IPFRs) at 14% dietary lipid than fish offered diets containing 8–10% dietary lipid, and displayed trends towards greater protein as a percent of whole-body composition at 8–10% dietary lipid. Sub-adult snapper in trials 3 and 4 showed no significant differences in growth, FER or survival. However, in trial 4 there was a general trend towards increased % weight gain (P=0.0615), FER (P=0.0601) and final mean weight (P=0.0596) with increasing levels of dietary lipid. Fish in trial 4 offered 6% dietary lipid also had significantly lower (P=0.0439) IPFR and PCE (P=0.0188) than fish offered 12% dietary lipid. Based on data obtained from these trials, inclusion of dietary protein at levels of 32–36% appears sufficient to support growth. For this level of protein, dietary lipid should be ∼10% in order to meet the energetic demands of the fish and to spare dietary protein for growth.

Notes: All-male populations of channel catfish, Ictalurus punelatus, were produced by feeding a diet containing trenbolone acetate to swim-up fry for 60 d. This hormone was effective in producing 100% males at doses of 50 to 150 mg/kg of diet. Fish that received 0 or 1 mg/kg of diet did not differ from the expected 1:1 sex ratio. Survival of control fish and fish fed diets containing trenbolone acetate were similar (P 〉 0.05) at the end of the treatment period and after a 60-d grow-out period. Our results represent the first report of successful masculinization of channel catfish with a synthetic anabolic androgenic steroid.

Notes: Abstract.— Trenbolone acetate (TBA) is a synthetic anabolic androgenic steroid approved in the United States as a growth promoter for beef cattle. Pooled populations of blue tilapia Oreochromis aureus with more than 98% males were produced by feeding diets containing TBA. This hormone effectively inversed the sex of blue tilapia when doses of 25–100 mg/kg of diet were fed for 28 d. Fish treated with 60 mg of 17-alpha-methyltestosterone (MT)/kg of feed resulted in 88.7% males. The percentage of male tilapia masculinized with TBA was significantly higher (P 〈 0.05) than with MT. Intersex fish were found in both control and hormone-treated groups, and were significantly more common (P 〈 0.05) in the MT-treated batches. Survival, feed conversion ratio, and average weight of O. aureus fry fed diets containing either TBA, MT or no hormone were not different (P 〉 0.05) at the end of the 28-d treatment period.