The estimation of fish length with back-calculation methods for some carp species living in Keban Dam Lake

In this study, it was aimed to estimate the lengths of younger individuals from the scale and otolith lengths by using the back calculation methods for Capoeta trutta (Heckel, 1843), Cyprinus carpio Linnaeus, 1758 and Luciobarbus mystaceus (Pallas, 1814) caught from Keban Dam Lake. For this purpose, 20 fish samples for each species were examined in October-November 2017. First the total length and weight of the fish were determined, then the scales and otoliths were removed. With the help of computer aided microscope, the length of the scales and otoliths of the fish, and the lengths of each age ring were determined. Fraser-Lee and Dahl-Lea back-calculation methods were used for the scale and otolith respectively. C. trutta were between 4-8 in age, 35.0-46.6 cm in total length and 382.0-987.3 g in weight. The mean total lengths of C. trutta calculated using back-calculation methods from scale ray lengths and from otolith lengths were estimated as L1: 21.4 cm, L2: 25.6 cm, L3: 28.1 cm, L4: 31.4 cm, L5: 35.0 cm, L6: 36.5 cm, L7: 38.8 cm, L8: 40.6 cm and L1: 18.6 cm, L2: 21.5 cm, L3: 24.9 cm, L4: 26.8 cm, L5: 30.3 cm, L6: 33.0 cm, L7: 35.2 cm and L8: 37.8 cm respectively. C. carpio were between 4-8 in age, 31.2-45.8 cm in total length and 442.5-1483.3 g in weight. The mean total lengths of C. carpio calculated using back-calculation methods from scale ray lengths and from otolith lengths were estimated as L1: 15.8 cm, L2: 21.3 cm, L3: 28.3 cm, L4: 30.6 cm, L5: 35.5 cm, L6: 38.0 cm, L7: 42.5 cm, L8: 44.7 cm and L1: 15.2 cm, L2: 18.9 cm, L3: 26.6 cm, L4: 28.4 cm, L5: 32.7 cm, L6: 35.6 cm, L7: 40.8 cm and L8: 41.3 cm respectively. L. mystaceus were between 4-7 in age, 37.1–47.4 cm in total length and 426.1-874.1g in weight. The mean total lengths of L. mystaceus calculated using back-calculation methods from scale ray lengths and from otolith lengths were estimated as L1: 7.7 cm, L2: 14.9 cm, L3: 21.4 cm, L4: 28.1 cm, L5: 30.3 cm, L6: 33.5 cm, L7: 35.6 cm and L1: 7.5 cm, L2: 14.5 cm, L3: 19.2 cm, L4: 26.3 cm, L5: 29.6 cm and L6: 33.3 cm respectively. In conclusion, in this study, total length values of C. carpio and C. trutta species calculated by using scale ray lengths were found to be closer to the measured values than the values calculated by using otolith length. In the L. mystaceus species, the values obtained by using both bony structures were lower than the measured values. For this reason, it is very important to use the most suitable bony structure for fish species to be estimated fish length by using the back calculation method.