Effects of synthetic androgen (17α-methyltestosterone) and estrogen (17β-estradiol) on growth and skin coloration in emperor red cichlid, Aulonocara nyassae (Actinopterygii: Cichliformes: Cichlidae)

Abstract

In recent years, the use of anabolic steroids in the coloration and growth of fishes, especially ornamental ones, has attracted great interest. In the ornamental fish industry, it is economically advantageous to produce some species with high commercial value and higher demand, depending on size, color, and sex. Therefore, the most commonly used steroids in this study—i.e., 17α-MT and 17β-Es (E2)—were added to the diet of emperor red cichlid, Aulonocara nyassae Regan, 1922, which has not been previously hormone-treated and has high economic value amongst ornamental fishes. A 60-day study was conducted in a closed system, where the juveniles of the emperor red cichlid were acclimatized with the control/basal diet for 15 days. After which, 15 fish with a similar shade of color and about 5 months old were weighed individually (0.71 ± 0.01 g). All fish were placed into aquaria (30 L) in five different groups, in triplicate. Five different groups consisted of control (without hormone), 50 mg · kg–1 17α-MT, 100 mg · kg–1 17α-MT, 50 mg · kg–1 E2, and 100 mg · kg–1 E2. The fish were fed a diet twice a day (10:00 h, 17:00 h) for 60 days till satiation. During the entire trial period, a 12 h light–12 h dark photoperiod was maintained. Water temperature was measured daily and recorded. Growth parameters of experimental fish were calculated. The color measurement of fish skin (L*, a*, b* values) from around the dorsal section was performed using a colorimeter (Konica Minolta CR 400). Significant differences were determined in the following parameters: weight gain (WG), specific growth rate (SGR), feed conversion rate (FCR), survival rate (SR), condition factor (CF), and sex reversal. The fish group fed with 17α-MT displayed brighter coloration as compared to other groups. Color analysis (instrumental) in terms of L*, a*, and b*, values showed that the group fed with 17α-MT displayed brighter coloration compared to other groups (P < 0.05). In terms of sex reversal, the fish in the 17α-MT groups exhibited 100% masculinization, whereas in E2 supplemented fish groups (50 and 100 mg · kg–1), the feminization rates were 88.88% and 93.33%, respectively. In conclusion, both hormones were found to have positive and negative effects for this fish species, but the 17α-MT hormone was found to be more effective in reversing skin pigmentation, growth, and sexing, which is the main driver in the ornamental fish trade.