Total length (TL), body weight (W) and the gonadosomatic index (GSI), the hepatosomatic index (HSI), and condition factor (CF) are important to evaluate the physiological condition of eel. While GSI is an important indicator of reproductive activity, the HSI reflects liver participation in vitellogenesis. The aim of this study was to evaluate these biological parameters of ell from Neretva Delta, Croatia, as a potential site for broodstock selection.
In February 2024, 14 eels in different silvering stages were chosen from fisherman catch in the mouth of river Neretva and analyzed. For each fish TL and W were measured. After dissection, gonads and the liver were taken and weighed. Fulton’s condition factor was calculated using the formula: CF = W/TL3 × 100. GSI was calculated using the formula GSI = gonad weight/W × 100. HSI was calculated using the formula HSI = liver weight/W × 100. The data was checked for normality using Shapiro-Wilk test. Homogeneity of variances was checked using Fligner-Killeen test. Normality of errors was checked using Shapiro-Wilk test. Pearson correlation coefficient was calculated to measure linear correlation of CF, GSI and HSI with TL and W. Linear regression was used to analyze the relationship of GSI and HSI with TL and W. To check for extreme values, Cook’s distances was plotted.
W values ranged from 59 to 1060 with a mean value of 343.86 ± 374.80. TL values ranged from 38 to 83.30 with a mean value of 52.66 ± 15.97. CF values ranged from 0.11 to 0.22 with a mean value of 0.15 ± 0.04. HSI values ranged from 0.59 to 1.58 with a mean value of 1.19 ± 0.27. GSI values ranged from 0.13 to 2.63 with a mean value of 1.26 ± 0.71 (Table 1).
A very strong positive correlation was recorded between CF and TL (r= 0.86), between CF and W (r=0.87). Strong positive correlation was recorded between GSI and TL (r=0.71; Fig.1.), while the correlation between HSI and TL was very weak negative (r=-0.05). A positive correlation was recorded also between GSI and W (r=0.61), while between HSI and W almost were no correlation (r= 0.03).