Actually, the harm caused by fishes is negligible in comparison to their benefits. Certain marine fishes like sharks and rays are extremely dangerous, and cause injuries and even death to swimmers and fishermen. They also damage the nets of fishermen. Some fishes (e.g. stonefish: Synanceia verrucosa) inflict wounds with their stings and insert poison that is very painful. Some electric fishes such as Torpedo are capable of generating electric shocks to man. Some fish species are the intermediate hosts of various parasites causing diseases in human and other animals.
Like marine fishes, some freshwater fishes also carry different types of toxic substances and these when consumed cause food poisoning or have carcinogenic effects. Some of these are as follows.
a. Ootoxin: This type of toxin is present in the eggs of some fishes such as catfish (Clarias spp.), asala (Schizothorax spp.) and common carp (Cyprinus carpio). Mature fishes have more ootoxin in their eggs. Consumption of such eggs without proper cooking might cause headace, diarrhoea, vomiting and fever.
b. Zootoxin: Certain catfishes such as Heteropneustes fossilis have zootoxin in their pectoral fin spine when they are alive. It inflicts by pectoral spine which is extremely painful and cause swelling of wounding place with fever. There is no harm if these fishes are eaten by proper cooking.
c. Haemotoxin: This type of toxin is found in the blood of some fishes. Certain species of eels (Anguilla spp.) have been reported to carry haemotoxin in their blood. Consumption of such fishes without proper cooking might cause vomiting and diarrhoea.
d. Tetradoxin: It is also known as puffer poisoning and is caused by some species of puffer fishes (Tetraodon spp.). The mature puffers contain a toxic substance called tetradoxin in the skin, liver, intestine and eggs. Tetradotoxin is neurotoxic and inhibits neural transmission even at relatively low concentrations (~2mg). These fishes when consumed without removing such organs lead to gastrointestinal disorders and neurological disorders such as paralysis, convulsions and respiratory failure leading to death. Thus, only highly trained and certified chefs are allowed to prepare this fish for consumption; a common practice in Japan where pufferfish are considered a delicacy.
e. Heavy metals: Fishes that live in industrial polluted water contain large amount of heavy metals and chemical toxins such as mercury, lead, cadium, dioxins and phthalates. Predatory and carnivorous fishes that feed on smaller ones generally contain higher amounts of such heavy metals (e.g., shark, tuna, freshwater bass, catfish, trout, etc.). Poisoning form such heavy metals and chemicals affects brain development and the nervous system of the developing foetus and child. The U. S. Food and Drug Administration (FDA) has recommended that the consumption of fish be limited during pregnancy and chieldbearing, with some fish such as tuna, swordfish and tilefish to be completely avoided.
Like marine fishes, some freshwater fishes also carry different types of toxic substances and these when consumed cause food poisoning or have carcinogenic effects. Some of these are as follows.
a. Ootoxin: This type of toxin is present in the eggs of some fishes such as catfish (Clarias spp.), asala (Schizothorax spp.) and common carp (Cyprinus carpio). Mature fishes have more ootoxin in their eggs. Consumption of such eggs without proper cooking might cause headace, diarrhoea, vomiting and fever.
b. Zootoxin: Certain catfishes such as Heteropneustes fossilis have zootoxin in their pectoral fin spine when they are alive. It inflicts by pectoral spine which is extremely painful and cause swelling of wounding place with fever. There is no harm if these fishes are eaten by proper cooking.
c. Haemotoxin: This type of toxin is found in the blood of some fishes. Certain species of eels (Anguilla spp.) have been reported to carry haemotoxin in their blood. Consumption of such fishes without proper cooking might cause vomiting and diarrhoea.
d. Tetradoxin: It is also known as puffer poisoning and is caused by some species of puffer fishes (Tetraodon spp.). The mature puffers contain a toxic substance called tetradoxin in the skin, liver, intestine and eggs. Tetradotoxin is neurotoxic and inhibits neural transmission even at relatively low concentrations (~2mg). These fishes when consumed without removing such organs lead to gastrointestinal disorders and neurological disorders such as paralysis, convulsions and respiratory failure leading to death. Thus, only highly trained and certified chefs are allowed to prepare this fish for consumption; a common practice in Japan where pufferfish are considered a delicacy.
e. Heavy metals: Fishes that live in industrial polluted water contain large amount of heavy metals and chemical toxins such as mercury, lead, cadium, dioxins and phthalates. Predatory and carnivorous fishes that feed on smaller ones generally contain higher amounts of such heavy metals (e.g., shark, tuna, freshwater bass, catfish, trout, etc.). Poisoning form such heavy metals and chemicals affects brain development and the nervous system of the developing foetus and child. The U. S. Food and Drug Administration (FDA) has recommended that the consumption of fish be limited during pregnancy and chieldbearing, with some fish such as tuna, swordfish and tilefish to be completely avoided.
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