UP research explores possible link to massive fishkill

Imagine the world without bangus. Imagine not having that succulent white meat in your sinigang. Dreadful! Now, perish the thought. It won’t happen. Not while marine scientists are looking for ways to protect aquaculture and prevent the massive death of cultured fish like our prized bangus.

One such marine scientist is Dr. Rhodora Azanza, dean of the UP Diliman (UPD) College of Science. Along with Leni Yap of the UPD Marine Science Institute, Azanza collaborated with Dr. Yasuwo Fukuyo of the University of Tokyo and Dr. Haruyoshi Takayama of the Hiroshima Fisheries Experimental Station to investigate the massive death of Chanos chanos (milkfish or bangus) aquaculture in Bolinao, Pangasinan three years ago.

Bolinao is not only the site of the UPD Marine Laboratory, but is also home to thousands of fishpens heavily concentrated on bangus aquaculture. Therefore, it is not surprising that UP was alarmed and that the alarm was translated into initiating this project.

A few weeks prior to the fishkill, students based in the marine laboratory and fishermen noticed reddish streaks in the water.

Samples of phytoplankton were immediately collected and analyzed. They were found to be the result of a Prorocentrum minimum bloom.

Prorocentrum minimum is classified as harmful algae. It produces toxins that can lead to red tide. This algal bloom was possibly caused by huge amounts of fish feeds that released large amounts of nutrients into the water.

While this was going on, fish behavior was observed to be normal. The fish were still eating the feeds given by the fishpen caretakers.

According to the study, toward the end of the bloom, "the fish started gasping for breath" and swimming to the surface. Some even jumped out of the water.

Hours later, it was not only thousands of cultured bangus which were found floating in the water, but also various reef fishes, eels, octopi, and sea urchins. The dead cultivated bangus were valued at P6 million or about $120,000. Total losses were estimated at P15 million.

Further analysis showed that the fishkill was caused by lack of oxygen in the fishpens. According to Azanza’s group, this oxygen depletion can be associated with the Prorocentrum minimum bloom.

The breakdown of the algal bloom and its decomposition decreased the dissolved oxygen in the water, which proved fatal to marine life.

Although the toxicity level of the Prorocentrum minimum cannot be confirmed as yet, Azanza’s group revealed that "culture of the organism has been initiated and can be used for possible toxicity testing and other biochemical and physiological studies."

The group recommended the constant monitoring of phytoplankton and "physico-chemical parameters related to blooms" to prevent damage in similar future events.

With proper management, a monitoring body, and a lot of help from the fishpen operators and caretakers, marine scientists and students, as well the government, the bangus — whether sinigang, inihaw or daing — will not be a thing of the past. — UP System Information Office