Hong Kong fish population under threat from oxygen-starved water, breakthrough study finds

Nutrient pollution from sewage creates conditions that can lead to reproductive problems that are passed down to offspring

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Professor Rudolf Wu warns that fish offspring produced by parents who had lived under hypoxia can also be affected, despite having never been exposed to the condition. Photo: K. Y. Cheng

Published: 12:04am, 30 Sep 2016Updated: 12:04am, 30 Sep 2016

Fish exposed to low or depleted oxygen levels in their marine environment – a phenomenon linked to algal blooms, or “red tides” – can develop reproductive impairments that are passed down to future generations, a team of Hong Kong scientists have found.

Defects include reduced testis size, sperm quantity, sperm motility and hormonal imbalances that cause more males to be born, disrupting the population, according to the latest breakthrough research.

The findings were relevant to Hong Kong where hypoxia, as the low-oxygen phenomenon is known, is commonly observed in bodies of water such as at Deep Bay, Shing Mun River and a major hotbed for nutrient-infused algal blooms – Tolo Harbour.

“Red tide” at Repulse Bay Beach. Photo: Edward Wong

When algae cells die, they sink to the ocean floor in large concentrations, consuming all oxygen as they decompose, and causing mass deaths of fish in the process. A hypoxic condition usually occurs when oxygen concentration falls below 2.8 milligrams per one litre of water.

“Hypoxia can cause [reproductive] impairments in fish and their offspring, [even if the latter] have never been exposed to the condition,” co-author of the study, professor Rudolf Wu Shiu-sun of Education University’s science and environmental studies department, said.