Jean-François Baroiller

Environmentally Relevant Concentrations of 17α-Ethinylestradiol (EE2) Interfere With the Growth Hormone (GH)/Insulin-Like Growth Factor (IGF)-I System in Developing Bony Fish

The aim of this study was to evaluate whether effects of environmental estrogens on fish growth and reproduction may be mediated via modulating the growth hormone (GH)/insulin-like growth factor I (IGF-I) system. To this end, developing male and female monosex populations of tilapia were exposed to 17alpha-ethinylestradiol (EE2) at 5 and 25 ng EE2/l water from 10-day postfertilization (DPF) until 100 DPF. Under exposure to both EE2 concentrations, sex ratio shifted toward more females and body length, and weight were significantly reduced in males. The growth-reducing effect was associated with significant changes in hepatic IGF-I expression, both in males and females and with significant alterations of IGF-I mRNA and GH mRNA in the brain. The changes in IGF-I and GH mRNA were accompanied by altered estrogen receptor alpha (ERalpha) expression in brain and liver. These findings point to an influence of estrogenic exposure on the endocrine GH/IGF-I axis. In addition, the EE2 treatment resulted in significant changes of ERalpha and IGF-I expression in ovaries and testis, suggesting that the estrogens interact not only with the endocrine but also with the autocrine/paracrine part of the IGF-I system. Overall, our results provide evidence that EE2 at environmentally relevant concentrations is able to interfere with the GH/IGF-I system in bony fish and that the impairing effects of estrogens reported on fish growth and reproductive functions may rather result from a cross talk between the sex steroid and the IGF-I system than be toxicological.

Endocrine and environmental aspects of sex differentiation in gonochoristic fish.

This paper reviews current knowledge concerning the endocrine and environmental regulation of gonadal sex differentiation in gonochoristic fish. In gonochoristic fish, although potentially active around this period, the hypothalamo-pituitary axis is probably not involved in triggering sex differentiation. Although steroids and steroidogenic enzymes are probably not the initial triggers of sex differentiation, new data, including molecular approaches, have confirmed that they are key physiological steps in the regulation of this process. Environmental factors can strongly influence sex differentiation in gonochoristic fish. The most important environmental determinant of sex would appear to be temperature. Interactions between environmental factors and genotype have been suggested for gonochoristic fish.

Main neuro-endocrine, endocrine and paracrine regulations of fish reproduction, and vulnerability to xenobiotics.

The reproductive function of fish, which is very sensitive to the variations of environmental factors, appears also to be particularly vulnerable to the presence of xenobiotics in the aquatic medium. Many physiological processes can be impaired, from sexual differentiation to female and male gametogenesis, due to disruptions among complex neuro-endrocrine, endocrine or paracrine regulations. This paper describes the main regulation steps that are known or can be suspected to be disrupted by xenobiotics and gives some examples. The large interspecific diversity of reproductive strategies and the complexity of underlying mechanisms are particularly highlighted to draw attention to possible confusions between real endocrine disruptions and natural physiological variations.

Sexual dimorphism in two pure cichlid species, Oreochromis niloticus niloticus (Linnaeus 1758) and Sarotherodon melanotheron melanotheron Rüppel 1852, and their intergeneric hybrids

Growth performances and sexual growth dimorphism were compared in two pure species of tilapia, Oreochromis niloticus niloticus (OO) and Sarotherodon melanotheron melanotheron (SS), and their reciprocal intergeneric hybrids (male O. n. niloticus × female S. m. melanotheron [OS] and male S. m. melanotheron × female O. n. niloticus [SO]). Fish obtained from artificial reproduction were reared on artificial diets over 10 weeks at 25 ± 2 °C, under light regimes of 12 h light:12 h darkness. Growth was measured on a weekly basis. Social interactions were recorded with a video camera. Pure O. n. niloticus achieved the fastest growth rates (Mean Specific Growth Rate (SGR) of 2.7 ± 0.6% d–1 for males and 2.3 ± 0.4% d–1 for female) and S. m. melanotheron the slowest (1.3 ± 0.3% d–1 for males and 1.4 ± 0.3% d–1 for females). The SGR of the intergeneric hybrids fell between that of the two pure strains. OS females grew faster (1.7 ± 0.4% d–1) than SO females (1.3 ± 0.2% d–1), whereas no difference was observed between males. Aggressive behaviour emerged first among faster-growing fish (O. niloticus and SO). The role of parental components in behavioural and physiological traits of tilapia is discussed.

Further Insights into the Insulin‐like Growth Factor‐I System of Bony Fish Pituitary with Special Emphasis on Reproductive Phases and Social Status

Insulin‐like growth factor (IGF)‐I, which is crucially involved in fish growth, differentiation, and reproduction, occurs in tilapia pituitary. IGF‐I peptide, which is probably produced in hypothalamic perikarya, is present in axons of the neurohypophysis, and IGF‐I mRNA and peptide are present in the adenohypophysis in adrenocorticotrophic hormone cells, melanocyte‐stimulating hormone cells, with interindividual differences in growth hormone cells, and, starting with puberty, in gonadotrophic hormone (GTH) cells. Subordinate males showed a high IGF‐I but a lower β‐luteinizing hormone expression, while in dominant males the opposite was found. IGF‐I from the GTH cells may act as auto/paracrine regulators of GTH cell proliferation and enhance GTH synthesis and release during puberty and reproduction, depending on the social status.