Disturbing surface water can prevent fishkill - expert » Nation » Article

Disturbing surface water can prevent fishkill - expert » Nation » Article

Disturbing surface water can prevent fishkill - expert
By Jun Pasaylo Home Updated June 03, 2011 02:52 PM 8 comments to this post

A fish pond worker scoops up dead milkfish after thousands of them were found floating on Taal Lake in Batangas. The Bureau of Fisheries and Aquatic Resources are still investigating the cause of the fish kill. (AP)

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MANILA, Philippines – Oxygen deficiency is the foremost reason behind previous incidents of fishkill and the current incident that devastated fishponds in Batangas and Pangasinan.

In an interview with philstar.com, fishery expert William Adan said fishermen should learn the importance of contact atmospheric oxygen and dissolved oxygen in the survival of fish and other water organisms.

Adan is a former chancellor of the Mindanao State University Institute of Fisheries and Development.

“During rainy days, freshwater create a thin film at the surface of the water, creating a buffer between atmospheric oxygen and the dissolved oxygen,” he said. He said this "thin film" caused by freshwater is the reason for the fish to drown.

He said fishkills can be prevented by the simple frequent disturbing surface waters.

He cited the importance of disturbing surface waters especially after a rainfall to “break the fresh water film” that settled at the surface for the oxygen to freely flow.

Incidents of fishkill frequently break out during night time because it is when the surface waters are undisturbed.

“If they don’t have aerators, at least they could have a boat crisscross above the fish cages or ponds to maintain a free-flow of oxygen supply,” he pointed out.

Another reason behind fishkills, he said, is the rapid development of sea organisms such as phantom algae during rainy days.

“These organisms grow faster and need oxygen for their photosynthetic activities; they compete with fish in the demand for oxygen,” he said.

He said that this is the reason why fishkill happen at night because “during nighttime, there is a decrease of dissolved oxygen in water, and these organisms compete with the fishes for oxygen.”

He cited the necessity to reduce fish stocking in the cages to increase the per fish oxygen allocation. He added that fishery workers must be educated on the feeding requirements of fishes.

He said that unconsumed feeds will develop into another kind of organisms that will also compete for oxygen with the fishes.

“It’s very important that they know that proper ratio of feeding their fishes,” he said.

Local government units in Metro Manila launched stricter monitoring to make sure that milkfish affected by fishkills in Pangasinan and Batangas will not reach public markets in the metropolis. Hundred of kilos of fishes, believed to be sourced from fishkill areas, were apprehended today in several public markers in Quezon City.

As of June 1, Taal Lake recorded 700 metric tons of dead milkfish while the municipalities of Anda and Bolinao in Pangasinan have 70 metric tons of spoiled fish.

“This has been a seasonal problem, but our fishermen never learn the lesson,” Adan said.