Age, Growth, Feeding regime reproduction and Sexual maturity of Rutilus frisii Kutum in Iranian coastal waters of Caspian Sea

Abstract

The project of Age, growth, feeding regime and fecundity of Kutum (Rutilus frisii Kutum) survey started in south of the Caspian Sea from 2006 to 2007. The aim of project was related to determination of length maturity (Lm50%), identification of feeding animals, and investigation some of biological aspects uncluded in sex ratio, growth and age structure in southern of the Caspian Sea. Total 2706 specimens of Kutum were surveyed. The age structure of Kutum has nine age groups that included in 1, 2, 3, 4, 5, 6, 7, 8, and 9 years. The result showed that maximum frequency was about 39.3 % and were belong to 4 years and minimum frequency which was about o.1 % were belong to 9 years. The maximum and minimum fork length and weight were 58 and 21cm with mean (±SD) 38.4 (± 6.4) cm; 2450 and 104g with mean (±SD) 784.2 (± 383.30) g , respectively. There are significant different between fork length and weight in male and female of Kutum at difference months (ANOVA, P<0.05). The sex ratio of males to female was 0.65: 1 (males: females). The least and high condition factor was 1.5 in January and 2.17 in October, respectively. Length maturity (Lm50%) was 39.07cm. Minimum and maximum absolute fecundity was varied from 15713 to 130737 eggs with mean (±SD) 69961.7 (± 3836.4). Significant different was between absolute fecundity with fork length and weight (p<0.05). Gonadosomatic index (GSI) mean for females were 2.5±0.2 (autumn) and 17± 0.2 (spring); 1.2± 0.1 (autumn) and 4.1± 0.2 (spring) for males, respectively wich coincided to spawning period. The highest feeding intensity (Gastrosomatic index) for females was 313.9 ± 65.9 in October and 119.4 ±59.2 in March; 350.7 ±103.7 in October and 144.1±85.04 in March for males, respectively. There are significant different between GSI with male anfemale in difference months (ANOVA, p<0.05). The Bertalanffy growth equation for all populations of Kutum was L (t) = 63.92[1-e ^0.19 (t (-1.00) ]. Main prey mature of Kutum was Cerastoderma lamarki; Gastropoda and Balanus were subordinate, and Crab, Hypanis, Fish (Neogobous sp.) Algae, egg, and scale were random preys. Planktone groups comprise to Exuviaella, Nitzchia, Osillatoria, Synedra, Nematoda, Navicolla, Diatoma, Rholcosphenia were preys juvenile of Kutum. Based on ISI (Important species index), Cerastoderma lamarki and Balanus were dominant species in feeding of Kutum. As a result, growth, fecundity and length maturity of Kutum declined which may due to loss natural breeding area, overfishing (overlapping between fishing and spawning period) and artificial breeding that commenced since 1982. Hopefully, this information can be used in fisheries management.