Effects of thyroxine administration on the growth and survival of pike silverside (Chirostoma estor) juveniles

The pike silverside has high aquaculture potential despite its slow growth. In this study, thyroxine (T-4) concentrations (0.13, 1.3 and 13 nM), a control with no hormonal supplement and a negative control containing 4.5 mM methimazole (MMI) were tested to evaluate the growth of this species. Juveniles (0.2 g) were exposed by immersion to these treatments for 8 h every second day for 120 days, and growth evaluations were performed monthly over the entire trial period. In addition, tissue samples from each treatment group were assayed for triiodothyronine (T-3) and deiodinase type 2 (D2) activity . The survival rates in all T-4 groups were high, and a significant increase in growth was observed (average of 58%). The MMI treatment caused an increase in mortality and a reduction in the final body weight compared with the control. T-4 administration did not affect the tissue levels of T-3, and it decreased muscular D2 activity only after 30 days of exposure. These results demonstrated that low concentrations of T-4 in the culture environment could improve the growth of this species without affecting tissue hormone levels. The technique may have useful applications for early-stage aquaculture of this and other economically important species.