| Summary: | This thesis investigates if boldness is reflected in the function of brain histaminergic system in zebrafish (Danio rerio). Moreover, behavioural differences in AB line, spiegeldanio (spd) line and wild caught strain of zebrafish have also been explored apart from the winner-loser effect in AB and spd fish. This thesis also includes studies on the effect of progestins on reproductive behaviour in zebrafish and regulation of leptinergic system on sexual maturation in male Atlantic salmon (Salmo salar L.). Boldness is reflected in higher expression of histamine receptor 1 (hrh1) in the telencephalon and diencephalon of male zebrafish and dominance by an elevated expression of hrh1 in the optic tectum. In female zebrafish boldness is also associated with lower expression of histamine receptor 3 (hrh3) in the optic tectum and dominance by lower expression of hrh3 in the telencephalon. Comparison of behavioural traits of zebrafish of AB, spd and wild type shows that wild type strain is most shy and shows no gender difference. AB is bolder than spd in the open field test while spd is bolder AB in the novel tank dive test. Similarly results for aggression are also test dependent since the spd is more aggressive than AB in the mirror test, however no difference is measured during dyadic fight test. A typical loser effect and activation of serotonergic system is observed in both AB and spd fish. Further, both levonorgestrel (LNG) and progesterone (P4) cause an early puberty in male zebrafish. However only levonorgestrel causes males biased population at environmental concentrations. In male Atlantic salmon, during early spring, both leptin paralogues, lepa1 and lepa2 in the liver and leptin receptor (lepr) in the brain are downregulated in non-maturing control group. At final maturational stage both hepatic lepa1 and lepa2 are upregulated 7.7 times and 49 times respectively in maturing control males. A significant upregulation of lepr is also measured from mid to late spermatogenesis. This thesis elucidates that an ...
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