Aquaculture or ‘fish-rearing’ used to be a rural affair . However, its scope and importance has been realized due to factors such as increased food production, relative higher cash income per unit area of the land, availability of fresh fish in areas where it was rare, improvement of nutritional status, and employment in the rural areas, etc.

The development in the aquaculture has also increased the production of preferred species and its exports have gone up. Foreign investment and joint ventures are also coming up. Simultaneously, new industries for manufacturing feeds and hatchery equipments are getting developed.

According to the figures compiled by the Ministry of Food and Agriculture, production of both, the inland and marine fish during the year 2002 stood at 181,000+473,000= 654,000 tons. These figures put Pakistan’s output ahead of many countries such as Germany, Iran, Australia, Algeria, Saudi Arabia and Israel.

Most of the fish-farms are inland. Coastal ponds depend on surface or underground water and are mostly located on wetlands with surface waters collected in flood areas. Such areas are, in fact, not wastelands, but have an important role in the maintenance of aquatic bio-diversity.

Ecosystem: Land-based farms have brought about ecological changes and have affected surounding areas. The subsoil water is frequently pumped out to fill these farms, which may lower the water table of the area. On the other hand, the use of sub-soil water in farms may result in reaching of salts in surrounding tracts, rendering these lands unsuitable for general vegetation and agriculture crops.

The coastal wetlands are considered more productive and provide nutrient to the organisms living in marshy areas. These act as a nursery for many commercially important fish varieties and other organisms.

Conversion of such areas into farms has affected the general marine ecosystem, and the introduction of exotic species in the aquaculture environment. These exotic species may work as a food competitor and other fauna. It has also a strong effect on birds through their breeding. The anti-predatory measures taken for farmers have direct effects on the bird population.

Chemical pollution: Effluents from aquaculture farms may contain chemicals used for disinfecting and controlling diseases, pests and predators. It may contain hormones, used for inducing, breeding and transfer of fish. All these may have adverse effect on other organisms in the environment. Aquaculture has many positive effects on the environment too. A few of theme are:

Recycling wastes: The aquaculture augments recycling of domestic and farm wastes. Animal wastes are considered a good organic fertilizer which is considered better than inorganic ones. Domestic wastes and human sewage can be used for fish farming. However, the use of domestic wastes is very restricted, because of the possible danger of transmission of human diseases. However, the combination of fish culture with waste treatment gives good results.

Thermal pollution: The heated water, discharged from power plants is considered dangerous to aquatic species, especially in the areas where the required temperature is not available. This can also help in saving the general aquatic environment from thermal pollution along with increasing fish output.

Poisonous fishes: At least, 1000 species are considered to be venomous. For the most part, these fishes are widely distributed throughout the world. Their number may sometimes be quite large in some areas. The term ‘poisonous’ is generally applied to those fishes whose tissues either, in part or entirety, are toxic.

The term, on the other hand is usually limited to those piscine which are capable of producing poison in a highly developed secretor organ or group of cells, and can deliver this toxin during an stinging act. Really, venomous animals are poisonous but all poisonous animals are not venomous.

The composition of most of the marine fish poisons is still unknown. But these substances are not nearly as common as they are in the terrestrial venomous animals. Some fishes venom provoke rather simple effect, while others provoke more complex responses.