Exogenous triiodothyronine application increases survivorship in larval lake sturgeon (Acipenser fulvescens): Molecular and endocrine regulation of appetite, growth, and stress axes

Abstract

Lake sturgeon (Acipenser fulvescens) are critically endangered across their native Canadian range and thus conservation aquaculture is practiced to restock historically decimated wild populations. However, as in many aquaculture settings, episodes of mass mortality occur throughout larval development and are often linked to periods of dietary transition. Thyroid hormones play a critical role in larval development and metamorphosis, including the transition from endogenous to exogenous feeding, and thus have been utilized in aquaculture to promote hatch rate, growth, and survivability in multiple fish species. The objective of the present study was to determine whether exogenous application of the biologically active thyroid hormone, triiodothyronine (T3), could improve lake sturgeon growth and survival during early ontogeny in two distinct rearing environments; tumbling jars representing hatchery conditions or egg mats representing more natural conditions. Waterborne application of 3 ppm T3 during fertilization improved growth and survival of lake sturgeon during the first month of life, with greater effects observed in the egg mat environment. Concomitant increases in mRNA abundance of genes involved in appetite regulation (e.g., neuropeptide Y and orexin) and somatic growth (e.g., insulin-like growth factor 1) support accelerated growth of T3 exposed fish through multiple neuroendocrine axes. Following the transition to an exogenous diet, transcript abundance was significantly reduced in the T3 group when compared to controls, perhaps indicating negative feedback regulation. T3 application also caused transient reductions in whole body cortisol content and reduced transcript abundance of genes related to the stress axis later in development; however, no apparent negative consequences were observed as a result. Finally, oral dosing of 3 ppm T3 during an exogenous dietary transition in juvenile lake sturgeon at ∼1.5 months post fertilization significantly increased sturgeon mass, but not survival, indicating that exogenous T3 can contribute to the success of young-of-the-year sturgeon during dietary transitions at multiple life stages. Therefore, these data demonstrate that elevated survivorship and growth associated with exogenous T3 application during fertilization are associated with upregulation of hypothalamus-pituitary-thyroid/interrenal, gut-brain, and somatotropic axes. Overall, exogenous T3 application represents a cost-effective way to positively influence lake sturgeon growth and survival at key dietary transitions during early development. Further, this study adds to a growing body of literature demonstrating beneficial effects of thyroid hormone treatment in fish aquaculture.