A total of 65 Rhinomugil corsula (Hamilton, 1882), measuring from 8.1 to 28.9 cm in length, were collected from the fishermen’s catch of the Sitakunda coast of the Bay of Bengal between March 2016 and February 2018 for morhpometric analysis. After collection, the specimens were transported to the Limnology and Fisheries Laboratory of the Department of Zoology, University of Chittagong with ice to avoid decomposition and then various measurements were taken, as soon as possible, using divider and measuring board having graduations in cm. Eye diameter and inter orbital distance were measured by slide callilpers (0.1 cm). Twenty seven morphometric characters were studied following the standard procedures described in Day (1889), Holden and Raitt (1974), and Joyaram (1981).
The following twenty seven morphometric characters were measured and investigated for each fish: Total Length (TL), Standard Length (SL), Fork Length (FL), Head Length (HL), Pre-Dorsal length (PDL), Length of the first dorsal fin (L1st DF), Base length of the first dorsal fin (BL1st DF), Length of the Second dorsal fin (L2nd DF), Base length of the Second dorsal fin (L2nd DF), Distance between first dorsal fin and second dorsal fin (DDF1&DF2), Length of pectoral fin (PecFL), Length of pelvic fin (PelFL), Distance between pectoral and pelvic fins (DPec&Pel), Anal fin Length (AFL), Base of Anal fin (BAF), Distance between pelvic and anal fin (DPel&Anal), Pre-anal fin length (PreAFL), Caudal fin length (CFL), Caudal peduncle Length (CPL), Maximum body width (MaxBW), Minimum body width (MinBW), Length of mouth cleft (MCL), Head Depth (HD), Eye diameter (ED), Pre-orbital distance (PreOD), Post orbital distance (PoOD), and Inter orbital distance (IOD).
The total length of each specimen was used as the basis of reference for all other measurements. The regression of various body characters of different specimens against total length were compared by using the covariance technique. For computing the growth of body parts in relation to total length of the fish, the rectilinear regression was used, because the use of regression of original measurements rather than ratios is time saving, easier to interpret and less likely to lead to confusing or doubtful conclusions as stated by Marr (1955). In the present study, linear regression of various body proportions against total length was fitted by the least square method after logarithmic transformation. The regression equation is represented as:
Log Y = a + bLogX
Where, Log Y = Length of body parts of the fish (dependent variables),
Log X = Total length of fish (or head length of fish for four variables),
a = intercept, and b = regression coefficient or slope.
In order to assess closeness of relationship, that might exist in different cases, correlation coefficient (r) for all the morphometric characters were also computed and tested by t-test.
The rate of growth of different variables was estimated on the percentage basis using the formula.