Aquatic life especially marine fish gave a bulk of food for mankind while fishes of the lakes and rivers are also important source for the food supply. Economically, the fishes constitute a very important group of animals. Besides being used as food, it provide byproduct of various kinds, such as fish liver is an important source of oil and has medicinal value which is used for the treatment of different diseases. Fishes also provide fish fertilizer, fish-manure and several other products of commerce.
The presence of helminth parasite up to large extent is dangerous for a fish population consequently, also causes a great loss of fisheries and the fishing industry. Parasitic infestation is greatly found in the fishes of Karachi coast.
During the present study, the marine fish Lutjanus argentimaculatus (Forsk, 1775) commonly called red snapper of the Karachi coast was studied for seasonal variation of helminthic infection and for cellular changes caused by these helminth parasites in various organs of this fish.
A total of twenty one species of endoparasites recovered, of them six trematode, eight nematodes, three acanthocephala, one cestode and three trypanorhyncha larvae.
The endoparasitic community had an overall prevalence of 74.89% with a mean intensity of 4.26. The parasite community was dominated by nematodes.
The effects of modifying factors such as season, length and sex of the hosts on the abundance of parasites were also studied. The infestation of parasites did not show any significant difference in male and female fishes.
The seasonal incidence of the total and as well as individual parasite species showed maximum prevalence during the hot (summer) seasons of the period. Presence of large variety of small fishes and other invertebrates in the stomach of this fish indicated their possibility as "carrier host" of the parasite.
Fish disease due to helminth parasite is one of the important problems in fish culture and fish farming. There are certain contagious diseases that destroy the stocks of fishes and constitute a serious danger to fish culture.
The result of histopathological changes in various organs by helminths parasite indicated the massive tissue damages in intestine, stomach and mesenteries resulting in erosions and formation of tunnels, mucous formation, dislocation of connective tissue, fibrosis, necrosis, atrophy, hypertrophy, lipodosis and mixed inflammatory response. The infected liver and spleen showed accumulation of melanomacrophase centers, cirrhosis, atrophy, haemopoitic tissue degeneration.
The risk of infection with fish-borne parasites present a potential or realized threat to the health of human consumers particularly in societies where the consumption of raw, undercooked on cold-smoked or lightly salted fish is traditional. Therefore, fish disease is one of the important problem because it has an indirect and sometimes direct effect on the productivity of fish in natural waters and on human health.
It is concluded that helminth parasites are very common in fishes of Karachi coast. More work should be carried out to study the affect of helminth parasites on various organs of different fishes.