Author Topic: Rotting fish due to fish-kills: another food for thought  (Read 5403 times)


  • Full Member
  • ***
  • Posts: 50
  • Karma: +1/-0
    • View Profile
    • Email
Rotting fish due to fish-kills: another food for thought
« on: June 04, 2011, 08:32:19 PM »
Rotting fish due to fish-kills: another food for thought
By Dr. Flor Lacanilao

Most fish kills in lakes and coastal waters occur where fish farming activities are excessive. A common suspect is pollution build-up—industrial & domestic wastes, agricultural fertilizers and pesticides, and fish feces and excess feeds. These dissolved nutrients can trigger phytoplankton or algal blooms and subsequent decay (using oxygen). The decay may be blown by wind in one area or settle at the bottom, then brought up by upwelling caused by wind or temperature changes. Algal blooms in coastal waters may also involve poisonous phytoplankton that, in high concentrations, cause red tide. The specific causal pollutant or factor in these environmental changes or fish kills is largely unknown.

What is known is that organisms have a capacity for tolerance to environmental changes, like pollution. The tolerance is limited and varies among organisms and with the kind of change or pollution. The tolerance is widest for survival, less for growth, and least for reproduction.

A given level of water pollution, for instance, may prevent an organism to reproduce but will allow it to grow. A higher level may arrest growth but will allow it to survive. At the limit of tolerance for survival, any factor of environment, whether man-made (e.g. pollution) or natural (e.g. temperature), can trigger fish kill that affects all species with similar tolerance properties.

Let me tell a story on fish pens in Laguna Lake, which in the 1980s was the site of fish diseases and deaths. It shows how unregulated practice of aquaculture give rise to conflict of interest, causing serious ecological, social, economic, and political problems.

In 1961-1964, when there were no fishpens at the Lake, the annual fish catch was 80,000-82,000 tons. In 1968, a survey showed that some 10,000 fishers used the Lake as a communal fishing ground. Harvest of shrimps and molluscs was about 240,000 tons; the bulk was used for animal feeds in the duck-raising industry.

There were 23 species of fish caught in Laguna Lake, with the goby (biyang puti) and perch (ayungin) as the dominant species. Carp, catfishes (hito and kanduli), snakehead (dalag), and tilapia were also caught in addition to migratory species from Manila Bay, through the once unpolluted Pasig River.

In 1971, the Laguna Lake Development Authority (LLDA) introduced fishpen culture with a 38-hectare pilot project. Milkfish (bangus) was chosen because of its market value and because it feeds on phytoplankton, which was abundant in the lake. The project gave encouraging results, producing 3.5 times more fish per hectare over that in open waters. The potential of the Lake fishpen aquaculture was estimated at 20,000 hectares and annual production value of P320 million. This prompted businessmen and entrepreneurs into fishpen culture. Development expanded to 4,800 hectares by the end of 1973; gross annual value was P77 million.

Data in 1982 showed that fishpens—then 31,000-hectares or one-third of the Lake—produced 62,000 tons. And the small fishers’ harvest from the open waters dropped to only 19,000 tons. They added up to a total Lake harvest of 81,000 tons, same as the yearly catch of the small fishers in 1961-1964 without the fishpens. This result was easily predictable from the start because both the cultured milkfish and the wild fishes depended on the Lake’s natural food.

As would be expected (because of competition for natural food), the uncontrolled growth of the fishpen industry led to longer rearing time—stretching the 4 months to 8-15 months. This led to supplemental feeding, which also allowed increasing the fish stock. Note that water would circulate in and out of the fishpens, bringing in natural food and taking out fish feces and excess feed that would then pollute the open-waters or settle at the bottom.

The conflict was between the community of poor fisherfolk (in the 1980s, more than 15,000 families) and the group of a few hundred rich fishpen operators. In a report published in the newspapers, the LLDA identified an elite group of fishpen operators owning 10 of the largest fishpens that add up to over 4,000 hectares (despite the fact that the the law says that no person or corporation can own more than 50 hectares of fishpen concessions). The list showed members of prominent families, including politicians and ranking military officers.

What the fishpens industry did was rob the small fishers of their traditional rights—by reducing their fishing areas and navigation lanes, by competing over the Lake’s budget of natural food, by polluting the waters, and by reducing their fish catch. Further, they ruined the Lake as a resource, which is important not only for fisheries but also for such other uses as water supply, irrigation, and navigation.

In his essay, “The Tragedy of the Commons,” Garrett Hardin points out that “the Tragedy of the Commons is an example of the class of problems with no technical solution. . . Therefore, any solution requires that we, as a society, change our values of morality” (Hardin 1968).

1. Lacanilao F. 1987. Managing Laguna Lake for Small Fishers. SEAFDEC Asian Aquaculture 9(3): 3-4.
2. Davis J, Lacanilao F, & Santiago A. 1986. Laguna de Bay: Problems and Options. White Paper No.2, Haribon Foundation.
3. See also “Extensions of ‘The Tragedy of the Commons” by Garrett Hardin. 1998. Science 280:682-683.

Dr. Flor Lacanilao obtained both his BS and MS in Zoology from the University of the Philippines in Diliman and his PhD, with specialization in comparative endocrinology, from the University of California at Berkeley. He served as professor and chairman of the Zoology Department at UP Diliman and chancellor of UP Visayas. He made pioneering discoveries in neuroendocrinology and led the research group that achieved the first spontaneous breeding of milkfish in captivity.
« Last Edit: June 07, 2011, 12:11:59 AM by florlaca »