Effect of graded level of protein in diet on growth, proximate and elemental compostion of fingerling Grass carp (Ctenopharyngodon idellus) from Souhtern Punjab, Pakistan

Abstract

Growth, external morphometry, proximate composition, and heavy metals concentration level in grass carp (Cetnopharyngodon idella) were studied. Different aspects of growth were studied in response to laboratory-prepared fish feeds having different crude levels of proteins provided to grass carp fingerlings. To study external morphometry and proximate composition, 72 samples of grass carp were randomly collected from the pond in which grass carp had shown best growth response to the feed which had 20% crude protein level . Fifty samples out of the total 72 samples were taken for evaluating concentration levels of twelve selected heavy metals. The study was conducted to assess the effect of three laboratory-prepared feeds having different levels of protein against control diet (containing rice polish only) on different aspects of growth of Ctenopharyngodon idella fingerlings. The trial period for this investigation was 90 days. Fingerlings were reared in four fish ponds, each having one acre surface area . Stocking density of the fingelings was 2000/acre. The fingerlings were hand fed @4% of body weight in the morning and evening during the trial period, six days a week on various diets T1, T2 ,T3 and T4(control) containing 15%, 20%, 25% crude protein level and rice polishing (control), respectively. Standardized methods were used in the whole trial. Average increase and percent increase in live weight and total length gain were monitored. Maximum daily growth rate, production, survival and specific growth rate were recorded in the fingerlings fed on a diet (T2) containing20% level of crude protein as compared to other diets having low or high crude protein levels. The lowest food conversion ratio (FCR) value of6.64 revealed T2 as the best feed composition. The diet having 20% crude protein showed maximum growth performance, specific growth rate, production, survival rate, etc.; therefore, T2 was the best feed composition for optimum growth of Ctenopharyngodon idella fish. Various morphometric characters, such as standard length (SL), head length (HL), head width (HW). body girth (BG), body depth (BD), dorsal fin length (DFL), forked length (FL), pectoral fin length (PtFL), pelvic fin length (PvFL), anal fin length (AFL), eye diameter (ED), tail length or caudal fin length (CFL), tail width (TW), wet body weight (W) with reference to total length (TL), condition factor (K) were studied to elucidate their correlations and types of growth. Correlation coefficient (r) value of 0.984 showed highly significant relationship between total length and wet body weight, while growth was negative allometric as 2.97 value of b was less than ideal slope value (b = 3). Regression coefficient value of condition factor (K) was 1.20  0.10, and significant relationship was observed between K and total length and body weight. Highly significant correlation (P < 0.001) was also found between body weight and various morphometric characters except for condition factor (K). The interrelationships of total length to SL, HL, HW, BG, BD, HW, BG, BD, DFL, PtFL, PvFL, AFL, ED, TL, TW were highly significant (P < 0.001). Proximate composition implies percent composition of water, protein, lipids, and carbohydrates. Standardized methods were used to find the proximate composition of 72 collected samples from a pond. Mean percent values for water were 80.76 %; ash 3.40 %; fat 4.31 %, and protein 11.53% in wet weight. Percent water showed inverse relationship with protein (dry & wet body weight), ash and organic contents (wet body weight). Wet body weight showed negative correlation with percent water, Percent fat (dry & wet body weight) and positive correlation with percent protein and ash (wet & dry weight). Total length showed negative correlation with percent water and fat (dry and wet body weight), and positive correlation with percent protein (wet and dry weight), ash and organic contents (wet body weight). Grass carp is rich source of protein, i.e. 58.35% in dry body weight, additionally, the pioneer reference on to proximate composition. To assess the levels of Ca, Cd, Cr, Co, Cu, Fe, K, Mn, Ni, Na, Pb, Zn; and their relationships to body size and condition factor, 55 fish samples were randomly selected and their concentrations were determined by ICP-OES after wet digestion method. Their concentrations were found to be within the normal limits. Cd, Pb, Cu, K, Mn, Ni, Na, increased isometrically; Cr, Co, Zn, had negative allometry, while Fe, Ca showed positive allometry with body weight increase. Ni, Mn, Pb, Cd, showed isometric increase; Na, K, Zn, Fe, Ca had positive allometry; while Co, Cu, Cr had negative allometry with total length increase. Ca, Cu, Fe, K, Mn, Na, Zn had highly significant relationships with body weight and total length. Most of inter- elemental relationships were found to be positive. Multiple regressions showed that Fe, Cu, Zn, Mn, Pb, Na, K, Ca, and Ni had highly significant relationship with total length and body weight. Since concentration of all the studied metals were within the limits set by FAO and WHO, therefore, intake of the studied fish is safe.