Effect of temperature on sex determination and growth of juveniles of Paralichthys orbignyanus sole
The present study analyzed the influence of temperature on sex determination and growth of juveniles of the Paralichthys orbignyanus sole. Right after the metamorphosis, juveniles (32.3 ± 1.6 mg) were distributed in 15 L tanks (30 fish per tank), where they were raised at 17, 20, 23 and 26°C. When they reached approximately 8 cm in total length, the fish were collected for histological analysis of the gonads and calculation of the percentage of males and females. On the 56th day of the experiment, they reached 608.8 ± 76.3 mg (23°C), 498.1 ± 88.1 mg (26°C), 443.7 ± 50.4 mg (20°C) and 318, 7 ± 22.1 mg (17°C), with a significant difference only between 17 and 23°C. The male-to-female ratio obtained at 20 and 23°C was close to the expected frequency of 1: 1. On the other hand, the percentage of females was 24% at 17°C and only 8% for sole reared at 26°C.A second experiment, with juveniles of 127.6 ± 31.9 mg, was carried out for 20 days with the same conditions as the first. The gene expressions of GH (growth hormone) produced by the hepatic and muscular adenohypophysis, IGF-I (growth factor type insulin I) were analyzed. The gene expressions of GH and liver IGF-I were similar, except for the higher expression of the first at 26°C and the lower expression of the second at 23°C. The expression of the muscle IGF-I gene in fish kept at 17°C was lower compared to the other treatments, while those kept at 23°C expressed more than those kept at 20°C and in both the expression was similar to those kept at 26°C, indicating the importance of the autocrine IGF-I in the growth of juveniles of sole. Right after metamorphosis, growth is optimized at 23 and 26°C.Due to the higher growth of female sole, it is suggested that juveniles are raised at 23°C. On the other hand, if the objective is the production of neomachos, the temperature used must be 26°C.