Fish: Fishes are included in the phylum Chordata, sub phylum Vertebrata andin the group of Pisces. They are very important aquatic natural resources of Bangladesh. Since the ancient time, fish is accepted as a popular normal protein food of men. Our 80% animal protein comes from fish. But along with the increase of population, the quantity of fish per head has been decreasing proportionally in the food list. Due to the construction of houses by filling up the ponds, ditches and canals, the cultivating fields have decreased and because of catching fishes in an unplanned way, the numbers of fishes are gradually decreasing. So there are two main reasons, for the decrease of fishes and fish resources. such as:
1. Natural reason: Due to alluvial deposits many of our rivers are filled up.The path of different rivers has been changed. As a result, the rivers have become inhabitable and unsuitable for fish reproduction. There have also been some changes in the periodicity of seasons.of Bangladesh. Due to the non appearance of rainy season in due time; and for draught, the rivers and canals become dried tip. This affects the habitats and Consequently the fish prodtuction.
2. Man made reasons: To meet the demand of fishes of the growingpopulation of Bangladesh, fishes are caught in an unplanned manner. Due to the increase of the number of fishermen, and as there are more than one owner of the same pond, the fish culture is not being properly carried out. To grow more rice, jute and other crops and to build the residential areas for man, many ponds, canals etc have been filled up and thereby the habitats of fishes are decreasing. Insecticides are used to control the pest of agricultural lands which are harmful for the fishes. These insecticides enter the ponds, rivers, canals, jheels etc along with the irrigated water and rain. This causes diseases and death of fishes and thus is unfit for human consumption. Due to the conservation, fishes have become very expensive and unavailable.