Just how do salmon find their way back to their spawning grounds? How do lampreys find their way to suitable spawning sites? They have the ability to “smell” their way. Salmon remember the exact chemical composition of the water in which they were hatched. Lampreys are able to detect minute amounts of hormones of resident “larval” lampreys. These are important for their survival as a species.
As such, fishes are inadvertently, great indicators of ecosystem health. So much so that they can sense chemicals that are beyond the detectable limits of even the most modern laboratory equipment.
There have been reports of higher than normal prevalence of female fishes in some waterways, influenced perhaps by chemical and/or hormones. This article details the factors that affect gender determination in fishes.
Begin forwarded message:
From: Dr Richmond Loh<thefishvet>
Date: 29 November 2011 12:36:14 AWST
To: thefishvet
Subject: Recommended article on ScienceDirect
Recommended Articles
Sent By: Dr Richmond Loh I thought you would find this useful on ScienceDirect.
1. Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences Review Article
Aquaculture, Volume 208, Issues 3-4, 21 June 2002, Pages 191-364
Robert H. Devlin, Yoshitaka Nagahama
A great deal of information is known regarding the process of sex differentiation in fish, and the mechanisms involved in primary sex determination are now beginning to be defined. A range of gonadal differentiation types have been described for fish, including gonochoristic species possessing purely ovarian or testicular tissues, as well as hermaphroditic species that can initially mature either as males (protandrous) or females (protogynous). Sex determination in fish is a very flexible process with respect to evolutionary patterns observed among genera and families, and within individuals is subject to modification by external factors. These influences can affect the fate of both somatic and germ cells within the primordial gonad, and include the action of genetic, environmental (e.g. temperature), behavioural, and physiological factors. Exogenous sex steroids administered at the time of sex determination can strongly influence the course of sex differentiation in fish, suggesting that they play a critical role in assignment of gonad determination as well as subsequent differentiation. Detailed information is available from fish systems describing the production of sex steroids, as well as the enzymes involved in steroid production. Both estradiol and the maturation hormone 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-DP) are produced by a two-step process involving different cell layers in the gonad, and have effects on the differentiation of gonadal and nongonadal tissues. Gonadal development and differentiation in some fish is also controlled by hormones from the pituitary gland (gonadotropins) that are regulated by release hormones (GnRH) and other neuroendocrine and gonadal factors. Genetic determination of sex in fish can involve monogenic or polygenic systems, with factors located on the autosomes or on sex chromosomes. In the latter case, both male (XY) and female (ZW) heterogametic systems have been described, as well as many subtle variations on these themes. Sex chromosomes are found in approximately 10% of fish species examined, and sex-linked phenotypic traits, and protein and molecular genetic markers have been identified in several fish systems. Some species of fish reproduce gynogenetically, producing all-female populations. Several gene families known to be involved in sex determination in other vertebrates have recently been shown to be similarly involved in fish, suggesting conservation of sex determination pathways. The lability of sex-determination systems in fish makes some species sensitive to environmental pollutants capable of mimicking or disrupting sex hormone actions. Such observations provide important insight into potential impacts from endocrine disruptors, and can provide useful monitoring tools for impacts on aquatic environments.
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