The effect of periphyton and supplemental feeding on the production of te indigenous carps Tor khudree and Labeo fimbriatus

Two experiments were conducted, one with the herbivorous mahseer Tor khudree and another with the fringe-lipped carp Labeo fimbriatus to study the effect of feeding and periphyton on their growth and production. Twelve tanks (25 m2) with mud bottoms and 0 (control), 98 (low density) or 196 (high density) bamboo poles tank(-1) were used. Mahseer (initial wt. 3.5 g) and fringe-lipped carp (initial wt. 0.73 g) stocked at 25 fish tank(-1) were reared for 90 and 60 days, respectively. Fish in half of the tanks received a pelleted feed (35% protein) at a ration of 5% body weight day(-1). Water was monitored daily for dissolved oxygen, pH, temperature, and Secchi disc visibility, and weekly for ammonia, nitrate, phosphate, and alkalinity. Periphyton dry matter, ash, and chlorophyll content were quantified fortnightly. Periphyton biomass, measured as total pigment (chlorophyll-a + pheophytin), decreased with time in both experiments indicating effective grazing by the fish. In the control treatment (without supplemental feed and substrates), mahseer grew to a final weight of 30.8 +/- 0.9 g and fringe-lipped carp to 19.1 +/- 1.1 g (mean +/- S.D.). Supplemental feeding alone resulted in higher final mean weight of mahseer and fringe-lipped carp of 38.3 +/- 0.6 and 22.9 +/- 1.2 g, respectively. The provision of substrates resulted in final mean weights of mahseer of 36.0 +/- 5.7 and 36.1 +/- 1.3 while that of fringe-lipped carp were 22.8 +/- 1.2 and 22.5 +/- 1.9 (low and high density, respectively). Net production of mahseer with substrates was 41% and 51% higher, and that of fringe-lipped carp was 43% and 75% higher than in the control (low and high density, respectively). The combination of substrates and supplemental feed resulted in mean final weights of mahseer of 40.3 +/- 0.4 and 39.7 +/- 1.2, and of fringe-lipped carp of 23.6 +/- 1.4 and 25.5 +/- 0.1 (low and high substrate density, respectively). Production of mahseer with a combination of substrates and feeding was 71% and 54% higher, and of fringe-lipped carp, it was 85% and 87% higher than in the control (low and high density, respectively). It is concluded that the provision of substrates can reduce the need for artificial feed and can be an alternative to feeding in the culture of herbivorous fish.