Abstract
One of the main goals of reproduction and fish is the production of a large number of viable gametes and high survival of offspring. In recent years, significant progress has been made in improving the efficiency of gametes production and progeny viability. However, there are still important gaps in the understanding of the physiological dynamic processes associated with gametogenesis. The knowledge of the structures that make up the gonads, as well as the all the neuroendocrine and molecular signaling mechanisms are of extreme importance in the elaboration of fish reproductive protocols. Among the challenges encountered, we highlight the wide range of fish species of different families, which, in most cases, have species-specific physiological mechanisms. In the neuroendocrine mechanism of fish reproduction, gonadotrophin releasing hormone (GnRH) is a neurotransmitter produced and secreted by the hypothalamus, which acts as a stimulatory factor on the release of LH and, to a lesser degree, FSH. Gonadotropic hormones (FSH and LH) act as the main regulators during vitellogenesis and maturation of gametes. It was believed that melatonin would be involved in the neuroendocrine mechanism in response to the photoperiod, inhibiting the release of GnRH. Recently, studies have shown that melatonin is also acting to accelerate the action of the maturation inducing hormone (MIH) and, consequently, the recovery of the meiotic cell cycle in carp. Thus, the objective of this review is to clarify the physiological mechanisms of the reproduction of teleosteos fish, starting from the description of the morphology of the gonads, understanding the neuroendocrine mechanisms and the molecular signaling
Highlights
One of the main goals of reproduction and fish is the production of a large number of viable gametes and high survival of offspring
In the neuroendocrine mechanism of fish reproduction, gonadotrophin releasing hormone (GnRH) is a neurotransmitter produced and secreted by the hypothalamus, which acts as a stimulatory factor on the release of LH and, to a lesser degree, FSH
It was believed that melatonin would be involved in the neuroendocrine mechanism in response to the photoperiod, inhibiting the release of GnRH
Summary
As gônadas de machos e fêmeas são órgãos pares, alongados, envoltos por uma cápsula de tecido conjuntivo fibroso, localizados dorsalmente na cavidade celomática (Koulish et al, 2002). O testículo lobular, o mais frequente, se caracteriza pela presença de inúmeros lóbulos, separados entre si por uma fina camada de tecido conjuntivo fibroso. Apenas na região do ducto espermático pode-se observar a presença de anastomoses dos lóbulos (Grier, 1993). A espermatogênese é um processo complexo que pode ser definido como um evento de proliferação celular, onde as espermatogônias se multiplicam por mitose e posteriormente meiose seguida de diferenciação das células filhas em espermatozoides. Schulz et al (2010) citaram três grandes fases no processo de espermatogênese: proliferação mitótica das espermatogônias, divisão meiótica dos espermatócitos e a espermiogênese, sendo a última, uma reestruturação das espermátides em espermatozoides, células flageladas É um processo que envolve células diploides originando células haploides (Quagio-Grassiotto et al, 2013). Schulz et al (2010) citaram três grandes fases no processo de espermatogênese: proliferação mitótica das espermatogônias, divisão meiótica dos espermatócitos e a espermiogênese, sendo a última, uma reestruturação das espermátides em espermatozoides, células flageladas
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