Sample Collection: The study was conducted during in 1 June, 2007 to 2 July, 2007. One hundred and three specimens were collected from the culture pond of Batiaghata in Khulna of Bangladesh. The age of the fishes was about one year.
Measurement of total length, standard length and body weight: At first the specimen was washed thoroughly with the clean tap water. The sample was taken in a tray and dried with soft cotton cloth. The total length was recorded in centimeter (cm) from the tip of the snout to the end of the tail and standard length of the specimen was recorded in the same scale from tip of the snout to the base of the caudal fin. The weights of the specimens were measured by means of a sensitive (3 decimal places) electric balance in gram (g). For determining the length-weight relationship, condition factor, relative condition factor, total length-condition factor, total length relative condition factor, of H. fossilis, “ SPSS-12” software and Microsoft office 2007 were used the following formula was also applied with respect to available references.
Length weight relationship: The relationship between the length and weight of a fish is usually expressed by the equation W=aLb or logarithmically Log W=Log a + log b log L by Ricker (1973), where W is body weight (g), L is total length (cm), a is the intercept and b is the slope according to Beverton and Holt (1996). Sokal and Rohlf (1981) mentioned that the parameters a and b of the length-weight relationships were estimated by the least-square method based on the predictive or Type I linear regression model, using W as the dependent variable and L as the independent variable. Spiegel (1991) reports that the degree of adjustment of the model studied is assessed by the correlation coefficient (r). Student’s t-test was applied to verify whether the declivity of regression (constant "b") presented a significant difference of 3.0, indicating the type of growth: isometric (b=3.0), positive allometric (b>3.0) or negative allometric (b<3.0) (In all cases a statistical significance of at 5% was adopted.
Estimation of condition factor: The condition factor was calculated by using the following formula:
K = W x 103 / L3 by Hile (1996). Where, W = weight of the fish in g; L = length of fish in cm; K = condition factor and 103 = the factor bringing the ponderal index or condition factor near unity according to Carlander (1970)
Relative condition factor (Kn): In the present study, relative condition factor (Kn) was also determined. Because Le Cren (1951) recommends the relative condition (Kn) as preferable to K, as in the former, the effect of length and other correlated factors are eliminated.
Relative condition factor was calculated by using the following formula: Kn = W/ W'
Where, W = Observed weight, W' = Calculated weight.