Fecundity Relationship, Maturity Size and Spawning Season of Shark Catfish Helicophagus waandersii Bleeker, 1858 in the Mun River, Thailand

A 48 shark catfish Helicophagus waandersii from the Mun River, Thailand was monthly sampled in 19 consecutive months (June 2003-December 2004) for studying in fecundity relationship, maturity size and spawning season. The fecundity ranged from 21,547 to 191,539 eggs. which the average was 85,174±43,206 eggs fish -1 The maximum fecundity belonged to a fish with 54.2 cm in total length (TL) and 1,067 gin body weight (BW) whereas the minimum fecundity belonged to a fish with 36.0 cm and 290 g. Fecundity increased with the increase oflength and weight. The regression equations offecundity (F) on total length (TL) and body weight (BW) were log F=0.8445+2.4518 log TL (r=0.67) and log F=2.8492+0.7308 log BW (r=0.7), respectively. The length at 50% maturity was estimated using frequency of occurrence of matured female was 42.01 cm which gave the expected fecundity as 66,933 eggs. Maximum GSI was in June and the minimum GSI was in November. Shark catfish was a group-synchronous spawner with a short spawning season during the rainy season from May to July. Shark catfish started moving from the Mekong mainstream since January and developed the eggs in the Mun River. After spawning, parental stock moved back to deep pools in the Mekong mainstream whereas the juvenile moved farther to the upstream floodplain for nursing and feeding purposes. Then it moved backward and joins with adult stock in September.