نشریه پژوهش های ماهی شناسی کاربردی
سال دوازدهم شماره 4 (زمستان 1403)

Tannin is an anti-nutritional compound found in acorns. The aim of research was to reduce the amount of tannin in the acorn through alkaline soaking process followed by fermentation and to investigate its effect on acorn in-vitro digestibility. Acorns were soaked in a 0.1 M sodium hydroxide for 8 hours. Then, the acorns were washed and soaked in distilled water for 16 hours. Subsequently, fermentation was carried out for 24 hours in 6 treatments with 0.5, 1.5, 3, 5, 10 and 15 g of bakery yeast per 100 g of acorns. The control was not soaked and fermented. Enzyme extraction was performed from the intestines of common carp with an average weight of 95.6 g. Significantly, crude protein in different treatments except the treatment containing 0.5 g of yeast increased by 5.8 to 186.5% compared to the control, but in all treatments, ash (8.4 to 48.2%), total phenolic compounds (56.8 to 68.4%), non-tannin phenolic compounds (57.4 to 73.8%) and concentrated tannins (87 to 95.6%) decreased (p<0.05). Carbohydrate digestibility in different treatments were 33.7 to 60.7 % lower than the control and protein digestibility in treatments containing 5, 10, and 15 g of yeast were 52.8, 103.8, and 145.3 % higher than the control, respectively. Due to the importance of improving the quantity and quality of protein in raw materials and reducing the amount of anti-nutritional phenolic compounds, the treatment containing 15 g of bakery yeast per 100 g of acorns is recommended for processing acorns by alkaline soaking-fermentation method.

The present study aimed to investigate the effects of different concentrations of thymol on reducing stress during short-term transportation of Caspian whitefish broodstock (Rutilus frisii kutum). The whitefish broodstock were caught from the Shi Rud and Sardab Rud rivers during the spawning season (April 2024). Twelve broodstock with an average weight of 910.25 ± 321.51 g for the Shi Rud River and 911.75 ± 384.06 g for the Sardab Rud River were selected and placed in four plastic bags (with a density of three fish per bag) exposed to thymol concentrations of 0 (control), 0.25, 0.375, and 0.5 mg/L for three hours of transportation. Afterward, blood samples were taken, and serum biochemical parameters were measured. The results showed that thymol significantly reduced glucose, cortisol, total immunoglobulin, and malondialdehyde while increasing the activity of lysozyme, complement, catalase, and superoxide dismutase (p<0.05). A comparison of the two rivers indicated that in the 0.375 and 0.5 mg/L thymol treatments, the glucose levels in the broodstock from the Sardab Rud River were significantly higher than those from the Shi Rud River (p<0.05). Cortisol levels were also higher in the Sardab Rud broodstock in these treatments (p<0.05), whereas in the control group and the 0.25 mg/L thymol treatment, cortisol was significantly higher in the Shi Rud broodstock (p<0.05). The activity of complement, total immunoglobulin, catalase, superoxide dismutase, and malondialdehyde was also significantly higher in the Shi Rud broodstock (p<0.05), while no significant difference in lysozyme activity was observed between the two rivers (p>0.05). Overall, it seems that using 0.5 mg/L thymol during short-term transportation can reduce stress in Caspian whitefish broodstock.

Non-native fish species, as one of the major threats to biodiversity, have been introduced by humans into various watersheds around the world for purposes such as aquaculture, recreational fishing, disease control, and more. The pond goby (Rhinogobius similis), a non-native and invasive species, has been reported in multiple watersheds, including the Caspian, Urmia, and Harirod basins. In this study, the presence of this species is reported for the first time in the Tigris River basin, along with a checklist of fish species from the Qeshlaq River. The findings highlight the urgent need for greater attention to prevent the spread of non-native fish species.

This research was conducted to estimate the growth and mortality dynamics of the common kilka (Clupeonella cultriventris) within its primary fishing grounds in the southern Caspian Sea, specifically in the Gilan Province, over the period from October 2022 to October 2024. A total of 688 specimens, comprising 250 males and 438 females, were subjected to biometric measurements and weight analysis. The mean total lengths of males, females, and the overall population were determined to be 12.79 ± 0.21 cm, 11.47 ± 0.12 cm, and 13.34 ± 0.15 cm, respectively. Statistical analysis of length-frequency distributions between sexes indicated a significant difference (DKS = 5.43, N = 152, p < 0.05).By employing the least squares method for model fitting, the asymptotic length (L∞) and annual growth coefficient (K) were estimated for the entire population, males, and females. For the population, these values were 15.85 cm and 0.48 yr⁻¹, respectively. For females, L∞ and K were calculated as 16.47 cm and 0.45 yr⁻¹, while for males, they were 13.95 cm and 0.62 yr⁻¹. The asymptotic weights (W∞) for females, males, and the overall population were 28.38 g, 16.58 g, and 24.42 g, respectively.Total mortality rates (Z) were also evaluated, with estimates of 1.76 yr⁻¹ for males, 1.33 yr⁻¹ for females, and 1.57 yr⁻¹ for the population in Gilan’s coastal waters. The marked reduction in the stock of common kilka highlights an urgent need for the implementation of robust fisheries management strategies to ensure the sustainability of this vital species in the southern Caspian ecosystem.

The aim of the present study is to estimate the optimal catch length for two mullet species , namely the leaping mullet (Chelon saliens) and the golden grey mullet (Chelon auratus), while considering uncertainty and sensitivity analysis. To record length, weight, and age data, 50 and 32 specimens of these two species were collected respectively from seining catches along the Golestan coasts during the period from October 2022 and April 2023. The parameters of infinite length (L∞ ) and growth rate (k) were estimated using two methods Ford-Walford and nonlinear least squares, while the natural mortality rate (M) was calculated using ten different approaches. The optimal catch length (Lopt ) for the two fish species was estimated under two scenarios: (1) calculating natural mortality from growth parameters estimated by the Ford-Walford method, and (2) calculating natural mortality from growth parameters estimated by the nonlinear least squares method. The age composition ranged from 0 to 7 years (with a fork length range of 13.8-28.8 cm) for the leaping mullet and 1 to 13 years (with a fork length range of 13.9-52.0 cm) for the golden grey mullet. The length-weight relationship analysis revealed slope values (b) of 2.81 for the golden grey mullet and 3.04 for the leaping mullet. Using the Ford-Walford method, the asymptotic fork length (L∞​) and growth rate (K) were estimated at 30.7 cm and 0.25 year⁻¹ for the leaping mullet, and 61.3 cm and 0.11 year⁻¹ for the golden grey mullet, respectively. Nonlinear least squares analysis yielded L∞​ and K values of 25.2 cm and 0.25 year⁻¹ for the leaping mullet and 47.7 cm and 0.16 year⁻¹ for the golden grey mullet. These same parameters estimated by the nonlinear least squares method for the leaping mullet were 25.2 cm fork length and 0.25 per year, and for the golden grey mullet, they were 47.7 cm fork length and 0.16 per year. The range of estimated natural mortality rates varied from 0.176 to 0.543 for the golden grey mullet and from 0.4 to 1.23 for the leaping mullet. The optimal catch length for the leaping mullet varied between 16.3–22.3 cm (mean: 18.6 cm) in Scenario 1 and 17.3–21.1 cm (mean: 19.6 cm) in Scenario 2. For the golden grey mullet, optimal lengths ranged from 24.1–42.3 cm (mean: 29.3 cm) in Scenario 1 and 23.6–33.3 cm (mean: 26.9 cm) in Scenario 2. The differences in optimal catch length calculations between Scenarios 1 and 2 were 18.2 cm and 9.7 cm for the golden grey mullet and 5.9 cm and 3.8 cm for the leaping mullet, respectively. These results indicate the significant impact of growth parameters and natural mortality on the estimation of optimal catch length. The final recommendation of this study for sustainable fishing management and the formulation of related regulations is to set the optimal catch lengths for the leaping mullet and golden grey mullet at 20 cm and 26 cm, respectively.

Fishing activity causes stress and physiological changes in the immune system. The aim of this study was to investigate the hematological, immune, and antioxidant capacity indices of male and female Caspian roach (Rutilus lacustris) in marine and pond conditions under fishing conditions. Hematological factors, except for the number of white blood cells, neutrophils and lymphocytes, differed between groups in the fishing conditions. Fishing stress in both sexes of sea roach caused a significant increase in the concentration of cortisol and glucose hormones. There was no statistical difference in the antioxidant enzyme of superoxide dismutase between the sea-caught and pond-caught groups of Caspian roach, while there was a significant difference in the catalase and malondialdehyde enzymes. Overall, the results showed that although fishing is considered as a stressor for aquatic animals, it wasn’t the main cause of changes in blood, immune, and antioxidant factors in the Caspian roach.

Fishing nets used in aquatic environments are sometimes abandoned or lost in the sea due to sea storms, torn or undiscovered fishing nets by fishermen, but they still catch aquatic organisms. Due to the lack of sufficient information on the abandoned fishing gears in the waters of Golestan Province, a study was conducted in this regard. For this purpose, in the Gorgan Bay and the Miankaleh Peninsula, the abandoned fishing nets were collected by anchoring from the spring to the winter of 2019. A total of 43 times anchoring, 6.5 km of fishing nets with weight of 425 kg were recovered from the sampling regions. A total of 1,005 aquatic animals with weight of 15.7 kg were caught in the discovered nets. The catch composition consisted of fish, crustaceans and seabirds. The main composition of the catch consisted of 73% of crustaceans (shrimp and crabs) in terms of number and 46% of seabirds in terms of weight. The results also showed that the amount of catch per retrieved nets was significantly different between summer and other seasons and the lowest amount of catch was obtained in summer. On the other hand, there was no significant difference between the average catch of retrieved nets in two depths up to 3 meters and 3 to 6.

Clupeonella caspia fishing in the Caspian Sea has played a significant role in the regional fisheries economy over the past decades. However, a sharp decline in the stock of this species in recent years due to overfishing, environmental changes, and the introduction of invasive species has posed major challenges to the sustainable management of these stocks. This study employs the Stock Reduction Analysis (SRA) model to assess biomass changes and predict the allowable catch of the Clupeonella caspia in the southern waters of the Caspian Sea. This research utilizes historical catch and biometric data of kilka species over the past two decades and applies the SRA model to analyze stock trends and sustainable harvesting rates. Various management scenarios, including fishing effort control, harvest limitations, and setting catch quotas, have been examined. The findings indicate a declining trend in kilka stock, with improper exploitation threatening the biological and economic sustainability of the industry. A comparison of the results with previous studies reveals an increasing share of Clupeonella caspia in the catch composition and a decrease in anchovy Clupeonella caspia harvests. Furthermore, the simulation of management scenarios suggests that implementing catch restrictions and optimizing fishing effort can play a crucial role in the recovery of this species' stock. Based on the study’s findings, it is essential to develop and implement sustainable fisheries management policies, such as setting allowable catch limits and regulating fishing efforts. Utilizing stock prediction models can assist policymakers in making informed and sustainable decisions. This study recommends continuous monitoring of Clupeonella caspia stocks and periodic assessment of their biological status to maintain ecological balance and ensure the long-term economic sustainability of the fisheries sector.