mehdi moradi chafi

The migration of fish to the sea requires the ability of osmoregulation to exposure to salinity, and changes in the structure and function of many organs, including the kidney, are involved in the developing this process. In this study, quantitative and qualitative changes in the kidney tissue of Caspian kutum (Rutilus frisii) fingerlings exposed to water salinity in the coastal and estuarine areas of the Caspian Sea were investigated. Three weighing groups 0.5, 1, and 1.5g were treated for 10 days in the three natural environments of the river (freshwater), the estuary (6-7‰), and the coast of the Caspian Sea (11-12‰) in the Kiasher beach area. At the beginning (0h) and end of the experiment (240h), 6 individuals from each weight group in each treatment were caught. After dissecting and separating the kidney tissue, the area and diameter of the glomerulus and Bowman's capsule were measured. The results showed that at the end of the experiment, the size of the kidney tissue indices significantly decreased (P<0.05) with the increase in salinity in all treatments. So that, the extent of this decrease in 1 and 1.5g weight groups was significantly more than the 0.5g group (P<0.05). Qualitative changes, including a decrease in the width of the proximal and distal convoluted tubule after exposure to salinity, were observed in all weight groups. The decrease in the size of the glomerulus in the estuary and coastal environments can be because constant drinking of water in these environments causes enough ions to be provided to the body and there is no need for large glomeruli for filtration. In the present research, two weights of 1 and 1.5g can compromise with the conditions of increased salinity of the environment when released and placed in the estuary and coastal environments of the Caspian Sea.

Three species Rutilus frisii, Alburnus chalcoides and Vimba persa are the most valuable fish that migrate to southern Caspian rivers especially Sefidroud river. In this study, the temporal and spatial distribution of was investigated based on presence and abundance of fingerling fish in 8 stations of the Sefidroud River, from the estuary to the Sangar Dam, during one year from March 2021 to December 2022.</span></span></span> According to the environmental conditions of stations, the sampling was done with an electrofishing instrument and a throwing net with mesh size 6 mm. The results showed that the abundance of fish fingerlings is minimal in the winter and their maximum abundance coincides with the reproduction time and after their adult spawning. The maximum abundance of these fingerlings along with their spatial distribution, also shows their migration pattern towards the Caspian Sea. The abundance of Rutilus frisii in the pebble and gravel beds of the upstream stations was the highest in April and the abundance of the Alburnus chalcoides and Vimba persa in the gravel-mud beds of the middle stations up to the estuary was the highest in August-September. The presence of Rutilus frisii fingerling, with an average weight of 2 g. was high in near to estuary in August while the other two species were present in the middle stations with high abundance until November. Rutilus frisii with weigh more than 3 grams in different stations in autumn and winter indicate the adaptability and residency of a number of fish in the river. The present study can provide some guidelines to the fish stocks restoration centers of Caspian Sea for releasing Kutum fry in the upstream areas, or fish fingerling in the middle of the river at an earlier time. This plan can be tested in a pilot program.

Silver carp, Hypophthalmichthys molitrix, is a plankton filter feeder fish and introduced to Chitgar Lake since 9 years ago. In this study, the effect of silver carp stocking was evaluated on the phytoplankton structure of Chitgar Lake at different seasons in 2018. Samples were caught with gill-net, beach seine and cast-net gears. The results obtained from 51 individuals with a total length of 111-473 (average total length of 325.8±134.6) mm showed that coefficient of vacuity, averages of relative gut length and feeding intensity were 0.00%, 5.91±1.65 and 628.4±274.7, respectively and therefore it showed over eating, herbivory and good feeding intensity in this fish. Silver carp fed on 32 phytoplankton and 11 zooplankton genera and phytoplankton and zooplankton were observed in 100% and 88% of studied specimens, respectively. Synedra, Navicula, Staurastrum and Cyclotella were the dominant phytoplankton genera (30.0, 22.2, 13.8 and 12.1%, respectively) and Bosmina and Alona were the dominant genera of zooplankton (84.0 and 7.2%, respectively). There were no seasonal changes in feeding intensity but there were seasonal changes in food items dominance. Releasing of 20000-30000 individuals of silver carp with a weight 50-100 g is suggested in order to protect water quality of Chitgar lake annually.

The study carried out in reproduction status project of commercial fishes of Anzali wetland from April 2016 until March 2017 and samples were caught using electroshocker in different points of studied area. The studied adult males (n=173) weight varied between 1.08 and 33.22 with an average of 7.12±4.06g and adult females (n=271) between 0.71 and 59.9 with an average of 12.66±9.16g. Total length were measured between 45.5 and 136 with an average of 80.02±14.03mm in adult males and between 41.3 and 166 with an average of 92.81±22.06mm in adult females, too. Age composition was from 2 to 11 and 1 to 15 years old for adult males(n=57) and females (n=130), respectively. Adult males and females formed 38.96% and 61.04% of adults. Monthly average of gonado-somatic index was determined 1% in August and 13.7% in April with an annual average of 6.54±7.08%for adult females. Spawning period of the fish species was determined on basis of gonado-somatic index and composition of gonad maturity stages of adult females from April to July. Absolute fecundity of studied fish (n=16) was calculated 3805-11483 with an average of 6898.1±1997.89 eggs and average of egg diameters was 0.9±0.1 mm. Although this fish has no economic value but this species is caught in Anzali wetland for consumption. Due to its Reproduction season, its overfishing should be avoided.

Neor Lake in Ardabil Province was ecologically degraded recently and the invasive fish Prussian carp (Carassius gibelio) has been dominated. In 2017, the biological study of this species carried out in order to control of its population in the lake. Fish samples were caught by different equipment; Gill-net, Cast-net and purse seine. The average weight of fish was seasonally varied between 59.76±36.25, 54.72±42.85, 102.66±26.32 g while the average length of fish was ranged between 146.20±36.51, 133.40±38.20, 174.41±13.04 mm. The age of fishes was about 2 or 6 years. Intestine length was varied between 2.8±0.28, 2.88±0.34, 3.19±0.34 mm and the condition factor was calculated 1.67±0.28, 1.85±0.16, 1.90±0.15. Feeding intensity was calculated 250.34±136.91, 165.11±64.11, 163.45±86.99. The Prussian carp feed mostly on detritus. Six phytoplankton and four zooplankton phylum were identified in their guts which Bacillariophyta and Rotatoria were dominant respectively. From their gut contents were identified 44 phytoplankton genus and 10 zooplankton genus that Synedra and Rotaria were dominant respectively. The range of length and weight of C.gibelio showed the unfavorable environmental conditions for feeding and living of this fish in Neor Lake. The range of length and weight of carp showed the unfavorable environmental conditions for feeding and living of this fish in Lake Inver.

Salmo trutta is one of the native fish that is endangered due to the sensitivity to environmental pollutants (entry of various pollutants including domestic, industrial, detergents, petroleum, etc.) of its generation. This study was carried out on 140 fresh salmon trout (Salmo trutta) fish from the mountainous region of Lar Lake in 2008 and 2009. The study their demographic structure. Based on Kruskal-Wallis non-parametric test, the statistical difference in gonadal weight (1.26 ± 0.016), relative weight of gonad (1.21 ± 0.020), Fulton index (1.50 ± 0.017) and Clark index (0.99 ± 0.015) was observed (p <0.05). T-test did not show any statistical difference in indexes such as body weight (153.44 ± 9.60 gr) and fork length (21.72 ± 1.85 cm) in both males and females at different ages (p> 0.05).