In this city alone, fishpens in Barangays Lucao, Carael, Tococ and Calmay lost P18 million worth of bangus last Tuesday.
Hardest-hit was Barangay Lucao with 69.7 hectares of fishpens, or 13 percent of the total 536.7 hectares, affected, city agriculturist Emma Molina told The STAR.
Molina attributed the fishkill to the sudden change of temperature due to the one-hour rainfall last Monday.
The water coming from the rivers of Binmaley might have also affected the fishpens here, she added.
"Because the low tide came at about 11 p.m. to midnight and then the high tide at 3 p.m., there was no flushing out of the old river water so it became stale, and that might have triggered the disturbance of the river floor. So the substrate, which had with it some pollutants like feeds, and the feeds that were (given) that morning (might have) caused a chemical reaction and triggered the fishkill," Molina said.
Based on the laboratory sampling done by the Bureau of Fisheries and Aquatic Resources, dissolved oxygen was very low at .9 part per thousand (ppt) in the upper stream and about .8 ppt at the bottom, thus making it hard for the bangus to breathe.
The normal level is six ppt, but bangus can also survive at three ppt, Molina said.
Because of the fishkill, Molina said they are strictly monitoring the bangus being sold in markets here.
"In fact, there were about three to four bancas full of bangus that came from Binmaley, which we did not allow to be unloaded because the fish was already showing (signs) of decomposition," she said.
Bangus affected by a fishkill contain a high level of histamine and could cause allergies, she said. They have bulging bellies and eyes, very white gills and a spongy body when pressed, she added.
In Binmaley town, the fishkill affected about P15 million worth of bangus, prawns and malaga (siganid) cultured in fishpens, fishcages and fishponds.
Municipal agriculturist Butch Ferrer said the affected bangus stocks were of marketable size (about P25 per piece) and post-finger size (weighing about 15 grams).
The affected barangays were Manat, Linoc, Gayaman, Amancoro, Biec, Nagpalangan and Lomboy, and part of the Dagupan-Lucao area.
In an emergency meeting called by Mayor Simplicio Rosario, the barangay chairmen of the affected areas promised to comply with the municipal fishery ordinance and to regulate the number of fishpens to prevent another fishkill.