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.

Natural Habitat Conditions in a Captive Environment Lead to Spawning of Spotted Gar

“…To date, several species of gar have been spawned in captivity via injection of gonadotropin releasing hormone (GnRH), which acts as an analogue to natural spawning hormones (Mendoza et al 2008;Amores et al 2011;Castillo et al 2013;David et al 2015). Documentation of breeding events in captivity that are not induced via administration of a hormone stimulus is much rarer.…”

Effect of cortisol and triiodothyronine bath treatments on the digestive enzyme profile and growth ofCatla catlalarvae during ontogenic development

“…Thyroid hormone accelerated development of the digestive structures, which increased digestive enzyme production at the beginning of exogenous feeding in alligator gar Atractosteus spatula and spotted gar Lepisosteus oculatus thereby imparting improvements in food utilization during the critical time of first‐feeding (Castillo et al . ). Faster digestive tract development and higher digestive enzymes activities during larval development may result in a higher capacity to digest more complex nutrients, promoting growth and increasing nutrient storage and survival rate of fish larvae.…”

“…Larval development to a fingerling depends on a proper development of digestive functions during larval life, and digestive tract maturation of can be altered by diet composition (Ma, Cahu, Zambonino, Yu, Duan, Le Gall & Mai 2005). Faster digestive tract development and higher digestive enzyme activities during larval development may result in a higher capacity to digest more complex nutrients, promoting growth and increasing nutrient storage, thereby increasing the survival rates of fish larvae (Castillo, Bollfrass, Mendoza, Fontenont, Lazo, Aguilera & Ferrara 2015). Thyroid hormones stimulated digestive processes in fish and lead to an enhanced absorption of ingested amino acids and peptides (Solbakken, Norberg, Watanabe & Pittman 1999).…”

Volitional Spawning of Captive‐Reared Age‐4 Alligator Gars

“…Castillo et al. () found that thyroid hormone treatments for broodfish and eggs improved reproductive performance and larval fitness, respectively. However, broodfish production has been considered an impediment to aquaculture due to the species’ protracted time to maturation (A. M. Ferrara and coworkers, paper presented at the World Aquaculture Society's Aquaculture America meeting, 2015).…”

“…Alligator Gar aquaculture has been studied by a group at the Universidad Aut onoma de Nuevo Le on, Mexico, who have spawned the species in captivity since 1982 (Mendoza et al 2008b) and developed an immunological method for gender identification (Mendoza et al 2012). Castillo et al (2015) found that thyroid hormone treatments for broodfish and eggs improved reproductive performance and larval fitness, respectively. However, broodfish production has been considered an impediment to aquaculture due to the species' protracted time to maturation (A. M. Ferrara and coworkers, paper presented at the World Aquaculture Society's Aquaculture America meeting, 2015).…”