Cases of Marine Fish Poisoning
By Rafael D. Guerrero III
Some marine fish become poisonous after feeding on toxin-producing organisms.
With the frequent occurrence of red tide on Philippines waters, the public has become wary and discriminating in its choice of seafood. The red tide renders bivalves like mussels, oysters and clams in affected coastal areas unsafe for human consumption. Fishes are generally not problematic as long as people remove their gills and entails before they are cooked and eaten.
There are instances, however, when marine fish poisonings do occur and lead to sickness or even death. Cases of ciguatera, pufferfish poisoning and goby fish poisoning have occurred in the country.
Ciguatera is a disease caused by the eating of toxic fishes that inhabit like red snappers, groupers and eels become poisonous when they prey on plant-eating fishes like the surgeonfish (“labahita”). These have, in turn, eaten blue-green algae present in coral reefs producing the poisonous substance.
The symptoms of ciguatera are prickling of lips, tongue and throat; numbness, nausea and vomiting. The victim may also experience dryness of mouth, abdominal cramps and insomnia. While the death rate for the disease is usually low, recovery is slow and may take several months.
The poison causing ciguatera is known as ciguatoxin. Although there is no known antidote for the disease, the intravenous administration of mannitol reportedly alleviates symptoms. The disease is common in the South Pacific where the incidence is estimated to be as high as 500 cases per 100,000 inhabitants. The fatality rate is a low 0.1 percent.
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Oyster and Mussels in Western Visayas
By Giselle PB. Samonte
Research should focus on increasing production and preventing red tides.
The slipper oyster (talaba) and the green mussel (tahong) are the only mollusk species being farmed in the Philippines.
The Western Visayas region in the central Philippines is one of the major sources of oysters and mussels, which are farmed for their meat. Production is mainly for the domestic market.
The need of the people in the region to augment their income from fishing has led to the proliferation of oyster and mussel farms.
The farms started operations as early as the 1950s. There are today an estimated 2,000 coastal families in the region which are engaged in the mollusk farming. Oysters are farmed along rivers using the bottom, stake, rack-hanging and raft-hanging methods.
In the bottom method, oyster shells or large stones are scattered on the sea bottom for oyster spat fall.
In the stake method, whole or halved bamboo poles are used as substrates for oysters.
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Oysters have been gathered from the wild for food long before scientific farming of the organism began. This bivalve is considered as one of man’s most nearly balanced natural food. It is a cheap source of protein and contains substantial quantities of all minerals and vitamins essential to the human diet. About 18% of the protein requirement, more than 50% of calcium and phosphorus, and all iodine and iron needed by an adult Filipino can be supplied by 200g of oyster meat. Aside from its edible portion, the shells of oysters are also used as raw materials for poultry and cattle feeds, fertilizers, pharmaceuticals and concrete products. Moreover, these can be recycled as cultches for collecting seeds. Other minor by-products include novelty items and ornaments
During culture period the oyster suffer from high mortality due to freshwater run-off brought about by heavy precipitation, adverse weather condition and abundance of fouling organism that are sometimes observed on collectors even prior to attachment of spats. These are some of the risks in oyster farming and to avoid these problems. It is necessary to conduct proper site selection for oyster cultivation. In general, a viable oyster farming ground should have the following characteristics:
- Water depth should ne 1.5-2.5m for traditional and at least 5.0m for non-traditional culture methods.
- Water salinity level is about 17-20 ppt and water temperature from 27-32 °C for faster growth.
- The area is not subjected to excessive flooding/freshwater run-off, which causes as mortality
- The site must be protected from strong currents and big waves. There should however, be moderate current for good water exchange to prevent build-up of decaying materials
- The site must be non-shifting or soft and muddy bottom to minimize siltationOyter beds should be free from predators and other natural enemies (borers, starfishes, crabs, etc.)
- Therse should be adequate cheap materials for cultch bamboo and empty oyster shells for spat collection.
- Presence of indigenous species of spawners to ensure adequate seed supply
- Materials for the farm structures should be readily available in the areaSite should be accessible and near to market outlets.
Four methods of oyster culture are practised in the Philippines; broadcast (sabong), stake (tulos), lattice and hanging (bitin, sampayan, horizontal, and tray) methods.
Broadcast (“sabog”) method. The broadcast method is the most simple and primitive method and it is adopted in areas with firm enough bottoms to support the collectors. Empty oyster shells, stones, logs and tin cans are scattered over the selected area where natural setting occurs. Oyster spats are grown to the commercial size on the collectors. The advantage of the method is the low investment required, whereas the major disadvantages are that it can be used only in coastal areas with firm bottoms and shallow waters, high mortalities due to silt and predation, and difficulty in harvesting.
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