Length-weight relationship and well-being factors of 33 fish species caught by gillnets from the Egyptian Mediterranean waters off Alexandria

Abstract

This study investigates the growth pattern of 33 fish species caught by gillnets from the Egyptian Mediterranean waters off Alexandria between 2018 and 2020. This is accomplished by studying the length-weight relationship (LWR), Fulton’s condition factor (k_c), the allometric condition factor (k_a), and the relative weight condition factor (k_n). The b-values of the length-weight relationship of the studied species varied between 2.1382 and 3.6868 according to the results. Only Dentex macrophthalmus (b = 2.1382), Etrumeus golanii (b = 2.4197), and Trichiurus lepturus (b = 3.6868) exhibited different values than the expected range of 2.5 < b less than 3.5. The 95 % confidence interval (CI) and Bailey’s t-test of b-values were tested. In terms of growth pattern, the results showed 20 fish species with an isometric growth pattern, 10 fish species with negative allometric growth, and only 3 fish species with positive allometric growth. The study of Fulton’s condition factor (k_c) assessed the differences between species to the differences in fish shape, and proposed that each fish family has its own range depending on the fish shape, and (k_c > 1) is not necessarily a better condition for the fish. The study of the allometric condition factor (k_a) assessed that the difference between k_a and k_c values influenced by the feeding intensity and the b-value. The values of the relative weight condition factor (k_n) were within the range from 0.929 to 1.038, and 24 fish species reflected a good growth condition while the k_n values for the remaining 9 species were less than 1.0. The obtained results add new data about specific species and provide updated data on the remaining species in the area of study. The obtained results can have useful effects on the stock assessment of fish species.