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Physiology & Neuroendocrinology
Affiliated research principals:
A major problem in aquaculture is the lack of reliable methods to spontaneously spawn captive broodstock fishes, primarily due to alterations in
neuroendocrine pathways in the absence of appropriate environmental, hormonal and behavioral cues. We investigate the roles of neuropeptides,
neurotransmitters, gonadal steroids and other factors in the control of reproduction using select marine fishes as experimental models.
A basic understanding of fish neuroendocrine systems will help develop innovative tools to enhance aquaculture productivity, as well as identify the
mechanisms of neuroendocrine toxicity of environmental chemicals.
Marine fishes are excellent vertebrate models to investigate the mechanisms of neuroendocrine control of reproduction.
In particular, We investigate the mechanisms of neuroendocrine control of gonadotropin-releasing hormone (GnRH) and gonadotropin release and
their gene regulation. We also investigate how multiple neuroendocrine pathways control puberty and sexual maturation in fishes.
Study Areas:
Neuroendocrine control of reproduction [Show Details]
The absence of appropriate cues for spawning in an enclosed environment can disrupt the neuroendocrine pathways that control hormones required for gamete maturation.
Mariculturists must understand the nature and extent of these alterations in order to develop innovative tools to modify and restore normal physiological responses
in species of interest. Neuroendocrine status of captive broodstock fish will be compared with their counterparts collected from natural spawning grounds.
The measures to determine neuroendocrine status include neurotransmitter metabolism, synthesis, and secretion of gonadotropin-releasing hormone (GnRH) and gonadotropins
(FSH and LH). So far, three distinct genes encoding three forms of the brain hormone GnRH have been identified in Atlantic croaker, cobia, and red drum.
Understanding the neuroendocrine mechanisms controlling multiple GnRHs in selected marine fishes is the major focus of research in Khan's laboratory.
Hormonal control of puberty [Show Details]
One of the important aspects of reproduction under the control of brain hormones, e.g., gonadotropin-releasing hormones (GnRHs), is the onset of puberty.
A basic understanding of this process will facilitate development of techniques to advance or delay puberty, or to produce sterile fish in order to enhance aquaculture productivity.
Neuroendocrine control of multiple GnRHs during puberty is being investigated in Atlantic croaker and cobia.
Hormonal control of sex change [Show Details]
A grouper species, rock hind, has been selected to study hormonal control of sex change. This species is a protogynous hermaphrodite, meaning they start out as females and the largest fish in
a group turns into a dominant male that maintains a harem consisting of several subordinate females. The experimental protocols have been developed where removal of the dominant male in the
group causes the largest female to change sex to a male. Some of the genes suspected to be responsible for this sex change have been cloned and other relevant research tools have been
developed to study control of sex change in this species. This basic research will lead to a better understanding of the reproductive biology of this important group of fishes, and will
be useful for fisheries management agencies tasked with maintaining healthy stocks. Captive rearing and spawning protocols to be developed for these species may also benefit future restocking programs.
Hormone-induced spawning [Show Details]
Lack of spontaneous spawning in captive fishes is often caused by impaired GnRH release. In such cases, slow release implants or injections
of synthetic GnRH analogs are very effective in hormone-induced spawning. Common snook is one of the important species in which this technology
is being tested in order to develop reliable spawning protocols. The long term goal of this research is to transfer new tools to fisheries management
agencies for potential restocking of this species in south Texas.
Development of hormone markers to identify gender [Show Details]
Early detection of gender can substantially reduce the cost of raising broodstock fish and abolish or at least reduce the need for collecting them from the wild.
Experiments to identify gender in red drum have been conducted in both cultured and captive fish (Kucherka et al 2006). This is the first study describing the sex steroid hormone profiles in red drum.
The results show that a minimum concentration of 11-ketotestosterone can be used to identify sex during early gonadal growth phase or even before the morphological sex can be differentiated.
Additionally, estradiol concentrations can be used to identify vitellogenic females (fish with partially or fully yolked eggs). These two steroids together can be used to distinguish gonadally
recrudescing males and females by a noninvasive method, which is a valuable asset in red drum broodstock management.
Neuroendocrine toxicity [Show Details]
Environmental chemicals can disrupt vertebrate reproduction by acting at multiple levels on the brain-pituitary-gonadal axis. Research in this area seeks to elucidate the mechanisms by which environmental
neurotoxic chemicals influence vertebrate reproduction, acting at the hypothalamic-pituitary (neuroendocrine) axis. These studies involve biochemical, cellular and molecular biological
approaches to understand the complex mechanisms of chemical interference with neuroendocrine pathways. This line of research is being conducted in collaboration with Dr. Peter Thomas at UTMSI.
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