Stimulatory effect of thyroid hormones improves larval development and reproductive performance in alligator gar (Atractosteus spatula) and spotted gar (Lepisosteus oculatus)

Abstract

Development of alligator gar (Atractosteus spatula) and spotted gar (Lepisosteus oculatus) larvae was evaluated after exposure of embryos to thyroid hormones (TH) by two different methods of administration. For the first method, alligator gar embryos were placed in a water bath with triiodothyronine (T3; 1 ppm for 2 h), and control treatment embryos were placed in a water bath without T3. For the second method, spotted gar adult males and females were injected with different TH during induced spawning: a group was injected with T3 [20 mg kg−1 body weight (BW)], a second group with thyroxine (T4; 20 mg kg−1 BW), a third group with thyroid-stimulating hormone (TSH; 4 IU kg−1BW) and a control group with dimethyl sulfoxide. Both methods resulted in increases in the concentrations of T3 and T4 in embryos of both species. An increase in the alkaline enzymatic activity of TH-treated larvae was observed as well as an increase in the RNA:DNA, RNA:Dry weight and DNA:Dry weight ratios at hatching. Some positive effects of TH application were: a significant increase in the hatching rate of spotted gar larvae from TH-injected parents and a higher percentage of successful spawns. Evenness of larval sizes and a higher survival rate were observed in alligator gar larvae. Snout development was accelerated by TH treatment in both species.