Lower levels of oxygen in water could lead to a higher ratio of male fish which might threaten certain fish species with extinction, according to a study result announced Wednesday by the City University of Hong Kong.
Professor of the university's Biology and Chemistry department Rudolf Wu, said a recent discovery showed that oxygen depletion, or hypoxia as it is known, could lead to more male fish and an imbalance in the sex ratio.
Such a discrepancy would have a dramatic impact on the reproductive success of certain fish, and could mean population decline and possible extinction.
This is the first ever report in the world of science that suggests hypoxia can affect the sex development, sex differentiation and sex ratio in an animal, and the result has been published in an international academic journal "Environmental Science and Technology."
According to Professor Wu, hypoxia can inhibit the activities of certain genes that control the production of sex hormones and sexual differentiation in embryonic zebra fish.
In his study, Professor Wu found that sixty-one percent of zebra fish, a universal freshwater fish model widely used in scientific and pollution research, spawned into males under regular oxygen conditions. Under hypoxia conditions, the ratio of males increased to 75 percent.
Hypoxia can be a naturally occurring phenomenon, particularly in areas where salt and fresh waters meet, in estuaries such as the Pearl River Delta, for instance.
In many places, hypoxic conditions nowadays are caused by pollution, such as nutrients, agricultural wastes and domestic waste water running into lakes and the sea along coastal regions.
To counter hypoxia, it was necessary to reduce by-products of human development such as, among others, human waste, industrial pollution, and fertilizers from farming, that impact the natural world.
This, Professor Wu said, would minimize the occurrence of eutrophication, a process in which water becomes enriched with nutrients resulting in a proliferation of plant life, such as algae, which reduces the dissolved oxygen content and can instigate the extinction of other organisms.