April 11, 2008

Major Philippine milkfish area warned of another fishkill

Fishery authorities warned fish cage operators in Pangasinan -- a major Philippine aquaculture province-- that oxygen level in waters in bangus (milkfish) ponds is dropping at alarming rates and could lead to another massive fishkill similar to the incident six years ago that wiped out cultured fish in the town.

Malcolm Sarmiento, Bureau of Fisheries and Aquatic Resources (BFAR) director, and town mayor Alfonso Celeste led the water quality inspection in several fish farms after reports showed that the dissolved oxygen level on Wednesday (April 9) was below 1 ppm (parts per million).

Westly Rosario, BFAR research centre chief said normal dissolved oxygen level is 5 ppm although 4 ppm is still acceptable.

Rosario said 50 dead bangus were seen on Wednesday when the dissolved oxygen level turned critical.

Municipal administrator Fred Castelo said at least one fish cage owner have salvaged some bangus a day prior to the critical water findings.

Sarmiento said the dissolved oxygen level improved from 2.5 to 3 ppm from 12 to 3 a.m. Thursday (April 10) in some villages.

The BFAR chief explains the dissolved oxygen level is at its lowest during those hours because no photosynthesis [the conversion by plants of light into chemical energy that produces oxygen] takes place until the sun is up.

He said though fish can still survive at 2.5 to 3 ppm, Sarmiento stressed cage operators should be prepared to take emergency action as oxygen levels could go down and cause fishkill.

Operators are advised to harvest their bangus if the level reaches at 2 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.

Although the dropping dissolved oxygen is considered is a normal occurrence during hot weather, Sarmiento said its main cause is still undetermined.