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<0.01).