BOLINAO, PANGASINAN – Fishery authorities warned fish cage operators here that oxygen level in waters where they culture bangus (milkfish) was dropping at alarming rates and could lead to another massive fishkill reminiscent of the one that all but wiped out cultured fish in the town six years ago.
Malcolm Sarmiento, Bureau of Fisheries and Aquatic Resources (BFAR) director, and Mayor Alfonso Celeste led the inspection for water quality in several stations on Thursday after reports showed that the dissolved oxygen level on Wednesday was below 1 ppm (parts per million).
The normal dissolved oxygen level is 5 ppm, although 4 ppm is still acceptable, according to Westly Rosario, BFAR research center chief.
He said about 50 dead bangus were seen on Wednesday when the dissolved oxygen level turned critical.
Fred Castelo, municipal administrator, said at least one fish cage owner harvested surviving bangus on Tuesday.
Sarmiento said the dissolved oxygen level improved to 3 ppm from 12 to 3 a.m. Thursday in the villages of Lucero, Binglas and Dungos. He said water tests in the Kakiputan Channel showed the dissolved oxygen level at 2.5 ppm.
It is during those hours that the dissolved oxygen level is at its lowest because no photosynthesis [the conversion by plants of light into chemical energy that produces oxygen] takes place until the sun is up, Sarmiento said.
He said fish can still survive at 2.5 to 3 ppm, but cage operators should be on alert as oxygen levels could go down and cause fishkill.
“They should be prepared to take emergency action,” Sarmiento said in a phone interview.
“There is no cause for alarm just yet but if the level reaches 2 ppm, operators are advised to harvest their bangus.”
Another team that monitored water quality in Anda, a town hit by fishkill in May last year, reported the dissolved oxygen level at 3 ppm.
Sarmiento said the number of cages in Bolinao fell to 350, about a third of the number of cages in February 2002 when the fishkill struck and brought at least P500 million in losses.
Sarmiento said the cause of the declining dissolved oxygen level is still undetermined, although “this is a normal occurrence during hot weather.”
“The most probable cause is the heat and the death of microorganisms,” he said.
