A Model of Hormonal and Environmental Involvement in Growth and Sex Differentiation in European Eel (<i>Anguilla Anguilla</i>)

Abstract

Growth in vertebrates is a complex interaction involving the development of cells, tissues and organs. Hormones regulating growth during maturation are involved mainly in the interaction between the somatic axis and the reproduction of brain-pituitary axes. Based on the results of hormone and gene transcriptions, the secretion and treatment controlling both the somatic axis and the gonadotropic axis were affected, directly or indirectly, by the environment parameter through hormones that were studied in my laboratory. A model was proposed for sex differentiation and gonadal development correlating to the growth of European eel (Anguilla anguilla). A high growth variation is affected by the environment. At a low density of eels, the gonadotropin-releasing hormone (GnRH) affected the secretion follicle stimulation hormone (FSH) in the pituitary, steroidogenesis and aromatase (CYP19) synthesis, and the 17β-estradiol (E2) from 11-ketotestosterone (Kt-11) causing ovary development. The ovary secretion E2 affecting the adenylate cyclase-activating polypeptide (PACAP), growth hormone (GH) and the insulin-like growth factor (IGF) stimulated rapid growth in females. On the other hand, a high density of eels caused the pituitary gland to secrete FSH at a lower level, and CYP19 was not synthesized in the gonads. The secretion of Kt-11 affected differentiation to testis, which inhibits the somatic axis in reducing growth rate.

Masculinization of Tropical Eel Anguilla bicolor McClelland in Different Population Density

“…Eel sex can be determined by the environment (ESD: Environmental Sex Determination) (Degani, 2016). According to Degani (2016), population density is one of the environmental factors that influence sex determination.…”

mRNA expression of growth hormone (GH) and Insulin during the initial ontogeny of tropical gar larvae (Atractosteus tropicus)

“…In this sense, during the development of the larvae of A. tropicus , the level of expression of digestive hormones was determined on the initial ontogeny, using the scheme based on live food (rotifers and Artemia). According to our results, insulin expression (INS) is present in small units from the development of the embryo (egg), increasing on day 3 DDE when it is in the stage of eleuteroembryon, and presents variations in expression during development, increasing considerably at 19 DDE, when it is already considered a juvenile, with the entire digestive system fully developed, including the complete formation of a functional pancreas (Frías‐Quintana et al., 2015), where the INS hormone remains active as it has been detected Scophthalmus maximus (Hu et al., 2012; Wen et al., 2015), Oncorhynchus mykiss (Mennigen et al., 2013), Platichthys stellatus (Xu et al., 2015), Anguilla anguilla (Degani, 2016) expression in specific organs in So lea senegalensis , Dicentrarchus labrax , Oreochromis hornorum , Trichogaster trichopterus , Acipenser gueldenstaedtii (Degani, 2014; Degani et al., 2017; Funes et al., 2006; Gao et al., 2012; Patruno et al., 2008) and in relation to other studies of insulin function and regulation in fish (Degani et al., 1999; Irwin, 2004; Li et al., 2006; Reindl & Sheridan, 2012) and other vertebrates in general (Jin Chan & Steiner, 2000; Rodgers et al., 2008). However, recent studies reveal that certain species of fish (fugu and zebrafish) have multiple copies of the INS gene, possibly as a result of an event of gene duplication associated with the appearance of teleosts (Conlon, 2001; Irwin, 2004; Wood et al., 2005).…”

“…In freshwater species, studies have been carried out to evaluate the effect of diets on the expression of the gene for growth hormone (GH) and insulin on growth and sexual differentiation in Anguilla anguilla (Degani & Abraham, 1992; Degani, 2016; Degani et al., 2003), GH secretion in Cyprinus carpio (Degani et al., 1999), GH expression and insulin‐like growth factor‐1 in Trichogaster trichopterus and Acipenser gueldenstaedtii (Degani, 2014; Degani et al., 2017; Goldberg et al., 2004; Yom Din et al., 2008).…”

Interspecific and sexual differences in riverine distribution of tropical eels Anguilla spp.

“…Although quantitative population densities could not be estimated in this study, assuming that sexually‐undifferentiated tropical eels tend to differentiate into females in the upper reaches where population densities are low and tend to be males in the lower reaches and small rivers where density is generally higher, differences in riverine distribution of the two sexes observed in this study is reasonably explained and is consistent with knowledge about temperate eels. Although the physiological mechanisms of sex determination and sex differentiation of anguillid eels is not yet understood (Degani, ), it is possible that the sex differentiation of temperate and tropical eels is caused by common mechanisms that may have been acquired at an early time in the evolutionary history of their catadromous life cycles.…”

“…Although the physiological mechanisms of sex determination and sex differentiation of anguillid eels is not yet understood (Degani, 2016), it is possible that the sex differentiation of temperate and tropical eels is caused by common mechanisms that may have been acquired at an early time in the evolutionary history of their catadromous life cycles.…”