Deluge of fresh water could be the cause

I REFER to the report, “RM100,000 worth of fish found dead” (The Star, Nov 28).

The fish were reportedly reared in suspended cages at the estuary of the Kinabatangan River.

The fish were saltwater species, mainly kerapu (groupers) and jenahak (presumably mangrove snappers), hence the cages were suspended in the estuarine location where the water is saline.

The Sabah Fisheries officials had taken samples to determine the cause of the fish mortality. I hope that they had also taken water samples in the vicinity to determine, apart from other parameters, the salinity of the water going through the cages.

From my earlier experience as a staff of the Fisheries Research Institute in Penang I had encountered similar instances of large- scale fish mortality in cages placed in the estuarine region of rivers, cages that were used for rearing saltwater fish.

My investigations then revealed that fish mortality was a result of a sudden deluge of fresh water from upstream due to a spell of heavy rain and that the fresh water would have most likely killed the fish in the cages.

Saltwater fish are unable to withstand a lowering of salinity to critical levels, especially when they are caged and unable to escape to safer areas down the estuary to the coastal zone where there is tidal effect.

ALEXANDER ANANDA JOTHY

Kulai Jaya

Johor