Abstract:
The aim of this study was to determine the abundance of fry to yearling size of kutum fish (Rutilus frisii), golden grey mullet (Chelon auratus) and sharp-nosed grey mullet (C. saliens), length, weight and age composition, sex ratio, condition factor, growth and morphological populations of these fish in Guilan province sea waters, and assessment of fecundity in kutum fish and study of natural propagation of kutum fish in some rivers of Guilan province. In the shores of Talesh, Anzali, Kiashahr and Chabaksar, the small fish were captured with seine net with mesh sizes 6 mm and large sized fish with seine net with mesh sizes 20 and 33 mm from winter 2020 to autumn 2021, but electro-shocker used for fishing fry and fingerling of kutum fish in 13 rivers downstream (from 40 to 1 km far from river mouth), in last April to last May, too. The results showed that Chelon saliens, Alburnus chalcoides, Atherina caspia and Neogobius pallasi in Guilan province shores were abundant using with 6 mm mesh-sized beach seine. The density of fingerlings camputed 18, 198, 839, 39 and 273 individuals for kutum (R. frisii), 201, 175, 578, 222 and 294 individuals for C. auratus and 1283, 1328, 1586, 541 and 1185 individuals in hectare for C. saliens in Talesh, Anzali, Kiashahr, Chaboksar shore and total stations. Spawning of kutum fish took place in 10 of 13 studied rivers, and it was verified the reproduction of 2 studied grey mullets, with sampling of fries, fingerlings and study of gonad or examination of anal of large samples in all stations of Guilan province, too. The averages of total length and body weigth in main fish species fingerlings in Guilan province shores in winter, spring, summer and autumn of 2021, respectively was measured 77.4, 96.7, 61.0 and 81.4 mm and 4.19, 8.13, 2.48 and 5.46 g in kutum fish (R. frisii), 44.1, 71.8, 97.2 and 34.7 mm and 0.79, 4.19, 9.31 and 0.47 g in golden grey mullet (C. autatus) and 65.3, 77.6, 53.7 and 60.8 mm and 2.95, 4.91, 2.38 and 2.56 g in sharp-nosed grey mullet (C. saliens). In this study on main fish species caught by different mesh size (6 to 33 mm) beach seine in Guilan shores, kutum fish had 0+-11, C. autatus 0+-12 and C. saliens 0+-7 years old, and this shows natural reproduction of grey-mullets and also kutum fingerling restoring have been done, annually. Sex ratio (male:female) was determined 1.38:1 and 0.83:1 in fingerlings (0+ and 1years old) and large fish (1+ and larger fish) in R. frisii, respectively; 1.5:1 and 1.09:1 in fingerlings and large fish in C. auratus, respectively and 2.11:1 and 1.15:1 in fingerlings and large fish in C. saliens, respectively, which there was significant difference in large kutum fish and in fingerlings of C. saliens between these sex ratio compare standard sex ratio (1male:1female). B value amount between body weight-total length relationship calculated 2.92, 2.94 and 2.91 for fingerlings of R. frisii, C. auratus and C. saliens, respectively and 3.08, 2.86 and 2.57 for adults of these fish species, respectively, and the growth pattern was positive allometric for the lare or adult R. frisii and negative allometric for the others, too. Condition factor value was determined 0.93, 0.94 and 0.94 for fingerlings of R. frisii, C. auratus and C. saliens, respectively and 0.94, 0.76 and 0.68 for adults of these fish species, respectively, which it highly decreased in large size of grey mullets (C. auratus and C. saliens). The averages of fork length was assessed 8.1, 25.1, 32.9, 37.9, 42.0, 46.5, 49.9, 52.8 and 56.1 cm in 1-9 years old of R. frisii, 8.0, 23.5, 28.3, 30.4, 34.9, 36.2, 39.6, 41.9, 43.3 and 48.6 cm in 1-10 years old of C. auratus and 9.0, 19.3, 23.5, 25.1, 25.7, 28.0 and 32.0 cm in 1-7 years old of C. saliens. Study of fecundity in adult female kutum fish with an average of the fork length 41.1 cm (n=15) showed absolute fecundity 23910-64606 (average,47025) eggs, relative fecundity 36800-69200 (average,50260) eggs per kg of body weight and eggs diameter 1.65-1.92 mm in fish from Kiashahr shore. In migrant kutum female into Sefidrud river with an average of the fork length 44.8 cm (n=98) showed working fecundity 23577-92029 (average, 49643) eggs, relative fecundity 25400-58100 (average,40700) eggs per kg of body weight and eggs diameter 1.67-1.99 mm, which increased absolute and working fecundity with increasing fish age and size but relative fecundity decreased via addition of age and size. The investigation of morphological variation in adults of of R. frisii, C. auratus and C. saliens, in different stations in all southern Caspian Sea with cluster analysis of body form showed that Hevigh and Tejan stations in a claster and the 6 other stations in second cluster with 2 sub-cluster in R. frisii, that it was highly amusing result; populations of Langroud, Chalous and Sari shores there were in a cluster and the 5 other stations in second cluster with 2 sub-cluster in C. auratus,, and Kiashahr and Sari shores there were in a cluster and the 4 other stations in second cluster with 2 sub-cluster in C. saliens populations, that it was predictable in 2 grey mullets, because of north-south and west-east migration, thus morphology and genetic study in one age class is simultaneously necessary for diffentiation of population. It is proposed investigation of spawning of kutum in all Iranian rivers of Caspian Sea and annual study of abundance, age compostion, growth rate and condition factor amount of all commercial fish species, in order to stock managing according updated data.
Keywords: Guilan shore, Guilan rivers, Rutilus frisii, Grey mullets, Reproduction, growth, Ecological population