Freshwater Shark (boal) a common freshwater carnivorous fish of Bangladesh, Wallago attu of family Siluridae, order Siluriformes. It also occurs in India, Pakistan, and Nepal. It is a voracious feeder and for its predatory habits it is popularly known as 'freshwater shark'. This fish lives in canals, ponds, haors, and other closed and open waters throughout Bangladesh. Large specimens may exceed 150 cm in length. Body is elongated, laterally compressed and scaleless; head depressed; 2 short and 2 long barbels are present. Mouth is large with sharp teeth on both jaws. Lower jaw is larger than the upper one. Gill openings are wide. Eyes are circular and are not covered by skin, situated above the angle of mouth.
The dorsal fin is small, while the pectoral is long. The caudal fin is homocercal with two unequal rounded lobes. The upper lobe is longer than the lower one. The lateral line is long. Generally, this species is not stocked in ponds because of its extremely voracious and piscivorous feeding habits. Breeding season of the fish is July and August. When ponds are flooded they may leave for shallow water for breeding. W. attu builds nest and shows parental care. [Md. Anisul Islam]