comparison of feeding prefrence and growth of grass carp (ctenopharyngodon idella) fed different plant with emphysis on chemical composition

for comparison of the food value of four different epecies of aquatic weeds: potamogeton pectinatus , potamogeton lucens, potamogeton perfoliatus, najas minor and two species of terrestrial grass: medicago sativa and cynodon dactylon by grass carp (ctenopharyngodon ideda), was studied in the shahicl rejai fishfarm in sari (province of mazandaran). totally 6 concrete ponds with 30 cubic meter volume free of any vegetation were used. each ponds was stocked by 25 fishes weighing about 150 gramms. different plant was given to each pond separately every morning during 60 days (july-august) experiment period. the results showed that food conversion rate from various weeds was different and the best belonged to medicago sativa (1: 19) and the worst to p. perfoliatus (1:50). in order to determine the nutritional composition of given provenders, chemical analysis methods were used. to measure protein, carbohydrate, fat, fiber, phosphorous and calcium, methods of folin-lowry, glucose standard curve, soxlet, methylthymol blue and ultraviolet were used respectively. percentage of protein and phosphorous of medicago sativa in dry weight showed the highest (17.5% and 0.6%). there was a good linear relationship between the quantity of chemical compostion and food conversion rate of different plants which could be positive or negative one. however protein and phosphorous played an important rule for achivieng a better conversion rate. the value of correlation coefficients between protein and phosphorous were r = -0.75 and r = -0.96 respectively, which the last one was statistically significant (p