نشریه پژوهش های ماهی شناسی کاربردی
سال سیزدهم شماره 3 (پاییز 1404)

The current study aimed to explore the diversity, abundance, and community structure of fish species over a one-year period, examining seasonal variations across six distinct stations along the Sirvan River. This research assesses spatial and seasonal fluctuations in biological indices such as Shannon, Simpson, Margalef, and evenness. Employing statistical and multivariate analyses, including ANOVA and clustering, enhances the understanding of ecological differences across various seasons and locations. The seasonal analysis of fish species abundance throughout the year indicated that their diversity and population density are significantly affected by seasonal variations.The findings revealed that the composition and structure of the fish community in the Sirvan River are considerably influenced by both temporal (seasonal) and spatial (station-based) factors. Increased biodiversity noted during warmer seasons (spring and summer) and in downstream stations with improved physicochemical conditions-such as stations 5 and 6-suggests a positive relationship between favorable environmental factors (e.g., elevated temperature, adequate dissolved oxygen levels, gentle flow, and suitable substrate coverage) and enhanced species diversity.Among the fish species identified, three-Carrasius auratus, Rhinogobius similis, and Carrasius gibelio-are recognized as exotic to the region. Overall, the observed trends in the Sirvan River illustrate the interaction of environmental factors, human activities, and the ecological characteristics of fish species. The results highlight that biodiversity is not merely a function of species count, but also depends on even distribution, functional composition, substrate conditions, and environmental threats. Consequently, ecosystem-based strategies should be implemented in water resource management to conserve and restore riverine biodiversity.

Illegal, unreported, and unregulated (IUU) fishing poses a major threat to aquatic resources, particularly in the southern Caspian Sea. This study investigates the illegal gillnet fishing of common carp (Cyprinus carpio Linnaeus, 1758) in the southeastern Caspian Sea region of Golestan Province during 2022 and 2023. A total of 12 illegal fishing boats were surveyed to record gear characteristics, catch composition, and catch per unit effort (CPUE). Interviews with 150 fishers estimated an average of 120 fishing days per boat annually. Using Monte Carlo simulations, the number of illegal boats was estimated to range between 900 and 1200. The average CPUE for common carp was estimated at 7.16 ± 1.43 kg/boat/day in 2022 and 8.75 ± 1.35 kg/boat/day in 2023. The estimated biomass of illegal catches ranged between 407–790 tons (2022) and 424–806 tons (2023). The highest fork length of carp was observed in spring (48.16 ± 2.25 cm), and significant differences in length distributions were found across seasons and gear types. Common carp accounted for the highest numerical and biomass percentages among captured species. The findings suggest that illegal catches of common carp were 7 to 10 times higher than legal catches, highlighting the urgent need for integrated and participatory management strategies to regulate and reduce IUU fishing in the region.

Heavy metals with their property of stability and indestructibility, accumulate over time in various tissues of aquatic organisms, including skin, bone, muscle, etc., and from this path enter the food chain and reach higher levels and consumption by other species are transferred. The present study was conducted to measure the amounts of heavy metals lead, nickel, zinc, iron and copper in the edible tissue of fish table islands (Qeshm, Hengam and Hormoz) in Hormozgan province. In the three mentioned regions, during the two seasons of summer and winter, a total of 180 samples were collected in 1398 (30 samples in each station and in each season separately). After bioassay, the concentration of heavy elements in the studied organ was measured using a flame atomic absorption device (Model 700Contr AA). The results showed that the highest mean concentrations of lead, nickel, zinc and copper were observed in Qeshm Island and iron metal in Hormoz Island and the lowest mean concentrations of metals were observed in Hengam Island. Metal concentrations in the analyzed samples were lower than international standards FAO, WHO, FDA, NHMRC and UKMAFF. Also, the level of potential risk and risk index for non-cancerous diseases in adults and children in the aquifer muscle tissue was less than 1. Therefore, it can be concluded that there are currently no problems for human health in terms of consumption of this fish.

In this study, the effects of manual and commercial rotifer enrichment with DHA on the survival, growth performance, digestive enzymes and antioxidant activities of yellowtail clownfish larvae (Amphiprion clarkii) were investigated. This  experiment  was  conducted  in  a  completely  randomized  design  with 3 experimental treatments (commercial enrichment of rotifer with Super selco, manual enrichment of rotifer with hand-made emulsion and control group) and  three  replications. The results of growth parameters analysis showed that the standard length and wet weight of larvae increased significantly in commercial and manual enrichment of rotifers with DHA, respectively. Survival rates of larvae were not statistically different mong the treatments during the larviculture period. According to the results, commercial enrichment of rotifers with DHA led to a significant increase in the activity of digestive enzymes lipase, protease and alkaline phosphatase of larvae compared to manual enrichment treatments and the control group. Also, the highest amount of malondialdehyde production and activity of antioxidant enzyme superoxidase dismutase was observed in commercial enrichment. In general, the results of this study showed, the use of commercial enrichment of rotifers, significantly improved the growth parameters and digestive enzymes and antioxidants, so this feeding strategy is advisable for proper nutritional management of larvae of this species.

Longtail tuna fish is one of the most important tuna and economic fish species in the south of the country, and the length-based index (LBI) model was used to describe the status of the Thunnus tonggol tuna stock in the northern areas of the Oman Sea. During 1994 and 2024, 3599 fish were biometrically measured (2010 in 1994 and 1589 in 2024), and the average length (range) of T. tonggol tuna fish in 1994 was 71±22 (125-38) cm and in 2024 it was 68±7 (122-28) cm. The average weight (range) of the longtail tuna fish in 1994 was 4231±2031 (1300-13000) grams and in 2024 it was 5629±2581 (700-22800) grams. Considering the calculated maturity length of this species (68 and 65 cm for the years under study), the percentage of specimens below maturity length in 1994 and 2024 was 32 percent and 48 percent, respectively, and the percentage of specimens below maturity length in 2024 was significantly different from that in 1994 (P<0.05).The relationship between the fork length and body weight of T. tonggol tuna fish was obtained for the year 1994 W = 0.067 L^ 2.64 (R2=0.80, N=550) and for the year 2024 W = 0.069 L^ 2.59 (R2=0.89, N=450) and the b value of the length-weight relationship indicating allometric (asymmetric) growth was negative. The average infinite length for the years studied 1994 and 2024 was 128 (105-133) and 125 (108-129) cm, respectively and the maximum length in 1994 was 125 cm and in 2024 was 122 cm. The optimal catch length range (Lopt) for the years 1994 and 2024 of the T. tonggol tuna fish in the northern waters of the Sea of ​​Oman was 73 (63-75) and 71 (59-74) cm, respectively, and the ratio of the mean length to the optimal length index (Lmean/Lopt) for the years under study was 0.82 and 0.79, respectively. The range of the mish size (MS) of the T. tonggol fish in the northern waters of the Sea of ​​Oman in the years under study 1994 and 2024 was 14.6 (13-15) and 14.2 (13-15) cm, respectively. The decrease in the average length, the increase in the percentage below the maturity length and the ratio of the average length to the optimal length can be evidence of the existence of overfishing of the longtail tuna fish in the northern waters of the Sea of ​​Oman (Sistan and Baluchestan Province).

Fish silage is an alternative to fish meal in livestock, poultry, and aquaculture feed industries. In this study, we aim to solve the challenge of drying fish silage by adding pistachio waste. First, the viscera of rainbow trout ensilage with acid, then different levels (10%, 30%, and 50%) of dried pistachio waste were added to the fish silage for co-drying. The results showed that the addition of 30% pistachio waste led to an acceptable reduction in moisture (16.18%) and a desirable increase in protein content (16.33%). In the second stage, the quality of the dried mixed product, containing 70% fish silage and 30% pistachio waste, was evaluated. The results demonstrated that the mixed product exhibited acceptable ranges for pH (4.93), total volatile nitrogen bases (43.87 g N per 100 g), peroxide value (3.82 meq oxygen per kg oil), and total aerobic bacterial count (2 × 10⁴ CFU/g), so that its quality is confirmed for partial replacement of protein sources in animal feed.  Mineral analysis showed that the mixed product is a good source of Calcium (12.69 mg/kg) and Iron (133.5 μg/g). In conclusion, the addition of 30% pistachio waste to rainbow trout silage leads to an economical drying process of fish silage, and according to its nutritional value of the mixed product, this product can be used as a protein supplement, a partial replacement for animal protein in livestock, poultry, and aquaculture feed.