Study of the growth pattern of kutum (Rutilus kutum Kamensky, 1901) in SefidRood River - Gilan Province

The kutum of the Caspian Sea has long been familiar with the life of coastal people, so that it has played a significant role in the economy of the coastal cities of the south of the Caspian Sea, and the living resources of the Caspian Sea, especially its economic fish stocks, have been seriously attacked in the past few years due to various crises. The study of growth parameters and intra-population structure makes interpretation, analysis and predictions related to the abundance of populations of a species possible, and Sefidrood River, as the most important fishing river of the country in Gilan province, plays a very important role in reproduction and stock enhancement of kutum. It was studied for a period of 10 years (2010 to 2019).The highest average total length and total weight for both males and females was obtained in 2014, which was 44.41 cm and 943.72 grams for males, and 50.49 cm and 1401.98 grams for females, respectively. Other years had significant differences (p < 0.05). The type of growth pattern for kutum population was obtained in 2013, 2014 and 2017 from isometric type, in 2010, 2011, 2012, 2015, 2016, positive allometric type and in 2018-2019 from negative allometric type. The highest value of the condition coefficient was obtained in 2019 and the lowest in 2015 (p < 0.05). The results showed that in all the studied years, total length and total weight also increased with increasing age for the population. The infinite length (L∞) in the populations in the 10-year period was between 73.11-87.74 cm. The range of growth rate (K) in this study for populations was between 0.08-0.19. Zero age index (t0) for populations was between -0.46 until -0.93, and Monro's Phi index (ф) was obtained between 6.18 until 7.28 in populations.