مجله علمی شیلات ایران
سال سی و یکم شماره 6 (پیاپی 134، بهمن و اسفند 1401)

Longtail tuna (Thunnus tonggol) is an important commercial species. This species is often caught in the Oman Sea by gill net. This study was conducted to study the selectivity of longtail tuna gill net based on the length-body girth relationship from January to July 2019 monthly in Bryce, Ramin, and Konarak sampling areas. For this purpose, the caught fish were collected and the data of Longtail tuna was measured from the eye, pre-operculum, operculum, and maximum body height at each stage of sampling. Then, the net selection curve and the optimal length of the longtail tuna were calculated by the gill net selectivity model based on the net mesh size. From the results, the maximum fish length was estimated at 40, 50, 56, 65, 68, and 80 cm for the net mesh sizes of 10.1, 11.4, 13.2, 14.6, 15.2 and 17.8 cm, respectively. According to Lm50 of longtail tuna at 73.3 cm fork length, the fish caught with mesh size of 17.8 cm has a fork length greater than the average sexual maturity length of the fish. Therefore, taking into account the catch of the target species, T. tonggol, the results showed that mesh size of 10.1, 11.4, 13.2, 14.6, 15.2 cm are not suitable for catching T. tonggol in the Oman Sea. The use of 17.8 cm mesh size with the purpose of catching adult T. tonggol would be suggested for sustainable and responsible fishing for this species.

Despite the importance of monosex fry production, due to incomplete gonad development in sex reversed male rainbow trout and the absence of sperm tubes, the use of diluents is necessary to improve sperm quality. In this study, in order to investigate the effect of sperm diluent on some reproduction indices, the results of experimental treatments: including (1) fertilization of diluted sperm of in sex reversed male fish with normal egg (2) fertilization of normal male sperm with normal egg and (3) fertilization of diluted normal sperm with normal egg were compared. According to the results of this study, the percentage of fertilization and eyed egg in the all-female eggs (treatment 1) were 80±1 and 79.3±0.6 respectively. Those indices in the mixed male and female population (control treatment, 2) were , 82±1. 80.3±0.6 and in treatment 3 were 72±1 and 79.3±0.6, respectively. Except for the percentage of fertilization, there were no significant differences for the other studied characteristic (P>0.05). The findings indicate an improvement in the quality of the sperm of sex reversed males using a diluent compared to the use of this substance in normal fish sperm. Increase in growth index, including specific growth rate and food conversion ratio in treatment 1 and 2 were 1.4±0.1, 0.9±0.1, and 1.3±0.1, 1.1±0.1, respectively and had a significant difference (P<0.05). The use of diluents to improve reproduction efficiency and no need to have a large number of male breeders in the farms in order to produce monosex fry, is completely desirable.

The object of this study was to investigate the status of physicochemical parameters and nutrients in demersal fishing grounds in the Iranian waters of the Persian Gulf from the Hormozgan province to Khuzestan province, from autumn and winter of 2017 to 2020. The local data of physical and chemical parameters of water were recorded and analyzed, by using a CTD (Conductivity, Temperature, and Depth)  device, during 2017, 2018 and 2020 years. Also, the sea surface temperature and chlorophyll-a were recorded from the MODIS (Moderate Resolution Imaging Spectroradiometer) satellite, aqua sensor, in 2018 and 2019 years. The average of remote sensing data of sea surface temperature and chlorophyll-a were 22.83 C° and 1.80 mg.m-3, respectively in the studied area, from 2018 to 2020. The average of local data of water temperature, chlorophyll-a, salinity and pH were 21.53 °C, 0.84 mg.m-3, 39.53 ppt and 8.28, respectively in the studied area during the years 2017, 2018 until 2021 winter. The average of concentrations of nitrate, phosphate and silicate were 0.034, 0.008 and 0.517 mg/L, respectively, in the present study. Based on the results, the amount of chlorophyll in the Persian Gulf has a relationship with the sea surface temperature and silicate. By increasing the sea surface temperature and concentration of silicate, the chlorophyll-a increases in the studied area. Changes in the concentrations of nitrate and phosphate had no significant effect on the concentration of chlorophyll-a in the studied area. The average of sea surface temperature and the concentrations of phosphate and silicate increased, but the concentration of chlorophyll-a and nitrite decreased from 2018 autumn to 2020 winter.

The present study aimed to investigate the effect of different feeding rates in summer condition (higher than 25ºC) on the growth and feed intake of juvenile Persian sturgeon (Acipenser persicus). For this purpose, four feeding rates including 1, 1.5, and 2% of body weight, and also based on appetite until satiety were considered in three replicates. A total of 20 juveniles with an average weight of 19.3±0.1 g were distributed in each concrete tank with a volume of 800 L and fed daily at 5, 11, 17, and 23 for 60 days. After 60 days, the results showed that in most of the measured parameters including final weight, final length, weight gain, body weight increase, and specific growth rate, the highest values were observed in the fish fed to satiation. Moreover, the amount of voluntary feed intake (as %/day) was observed in the satiety level and the lowest feed conversion ratio was measured in the fish fed with 1.5% feeding rate. There was no significant difference in condition factor among treatments. Based on the voluntary feed intake, the results showed that fish in this condition need 2.4% of feeding rate per day. This study showed that it is possible to easily culture and feed juvenile Persian sturgeon in summer condition at high temperatures without any problem and to achieve the highest growth and feed efficiency, the feeding level of 2.4% of body weight per day is recommended in the present experimental conditions.

Water pollution is a major global problem that affects plants and living organisms. Factors affecting water pollution include industrial, agricultural, and human pollutants. Qarasu river is very important in terms of pollution due to the use of river water in the agriculture and aquaculture sectors. In this research, the effect of intensive fish farms and the riverbed material was investigated on the abundance of macrobenthic communities. For this purpose, four stations 1) the station upstream and before the fish farms (as control station), 2) the station between the fish farms, 3) the last station of the farms, and 4) the downstream station at a distance of 4 km from the last farm were selected. A sampling of the macrobenthos and riverbeds was done in two seasons, winter and spring, and their frequency was calculated in the sampling stations and months. The highest abundance was related to the family’s Chironomidae (1456 numbers per m2) and Simolidae (2737 numbers per m2) from the Diptera order, which were observed in the effluent of station 2 and station 4 in the winter season, respectively. In addition, the type of the river bed was determined to find the correlation with macrobenthic species. The identified macrobenthos was classified into trophic groups and the relationship with the type of substrate was determined using the Pearson correlation. The correlation of different macrobenthic species with sampling stations and months was found using Canoco software and CCA statistical analysis. The present study showed that the effluent from intensive fish farms had an effect on the abundance of macrobenthos in the Qarasu River, which could be due to the increase in nutrients in the river water from the release of the effluent, and decrease in temperature and decrease in the decomposition of nutrients in the winter season. Therefore, based on the findings, the presence of different functional macrobenthic groups is affected by the type of riverbed and different seasons of the year.

In order to investigate the population structure of the whitefin wolf herring (Chirocentrus nudus) by morphometric and meristic characters method in the waters of the north of the Persian Gulf, from the three regions of Abadan, Shif and Bandar Abbas, 20 individual from each station and A total 60 fish was collected by gill net and it was prepared and transferred to the laboratory in May 2019. 29 morphometric traits and 5 meristic traits were measured. The results of the one-way analysis of variance of 12 morphometric characteristics among the samples had a significant difference at the 5% level, which indicates the phenotypic diversity in the whitefin wolf herring of the three studied regions. The results of the discriminant function analysis (DFA) about the morphometric traits showed that the populations of the whitefin wolf herring in Abadan, Shif and Bandar Abbas regions were separated from each other by 91.7%. The results of principal component analysis (PCA) for morphometric traits showed that 9 factors with eigenvalues ​​greater than 1 were selected, which includes 84.56% of the variation of morphometric traits. Based on the Kruskal-Wallis test, among the 5 meristic traits measured, two traits including the number of spines and rays of the dorsal fin and the number of soft rays of the pectoral fin were found to be significantly different at the 5% level (p≤0.05). The distribution diagram based on the first and second components, the dendrogram of the morphometric traits showed that there are at least two different populations of the whitefin wolf herring species in the Persian Gulf.

To study the growth characteristics of Alburnoides cf. tabarestaensis with 234 fish sampled in obtained in April 2018 to August 2018 with electroshocker. Sex ratio of male to female was 1:0.93 that showed there was no significant difference between sex ratio of male to female in population (X2=1.709, p<0.05).  Maximum total length and weight were 78 mm and 5.60 g for females, 68 mm and 4.32 g for males, repectively. The weight - length relation of female was W=0.0088 TL3.25 and the weight - length relation of male was W=0.0064 TL3.46 and the total relation was W=0.0079 TL3.33. The results showedpositive allometric growth for this species (t-test, t male=5.08, t female=2.99, t population= 5.03, p<0.05). The condition factor analysis showed that the lowest quantity for both sexes was obtained in May (0.69 and 0.76, respectively) and the highest was obtained for male and female in June (2.55 and 1.36, respectively). The highest instantaneous growth rate was observed for both males and females at zero to one year old (0.86 and 0.73, respectively). Growth rate (K) in males (0.23) was higher than females (0.12). Zero age index (t0) was negative for all groups (males, females and population) and was obtained for males -2.94 and for males -3.51. Growth parameters were estimated as L∞=82.08 mm for males, L∞=119.42 mm for females and L∞=93.38 mm for population. Von bertalanffy growth equation was estimated as Lt=119.42(1-e-0.12(t+3.51)) and Lt=82.08(1-e-0/23(t+2.94)) for female and male fish, respectively.

Cadmium (Cd) is a heavy metal that is considered a strong pollutant due to its long half-life in soil and high solubility in water. This metal is toxic and the main pollutant of aquatic ecosystems. In the present research, the effect of adding pomegranate peel extract in the diet of common carp (Cyprinus carpio) on inhibiting oxidative damages caused by experimental poisoning with cadmium has been evaluated. In this study, fish with an average weight of 70 g were randomly divided into five groups of twenty. The first group, without receiving any feed additive was considered as a control. The second group of fish was only exposed to cadmium chloride (5 mg/l). The third, fourth, and fifth groups, in addition to cadmium (5 mg/L), they also received 1, 2, and 4% concentrations of pomegranate peel extract, respectively. After the end of the test period, which was 140 days, the blood collection was taken from the samples. Then, the biochemical parameters in the blood serum of each sample were measured. The evaluation of the activity of enzyme indicators showed that cadmium consumption significantly decreased the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx) and total antioxidant capacity (TAC), while the level of malondialdehyde (MDA) increased significantly (p<0.05). Also, the results showed that the addition of increasing concentrations (1, 2 and 4%) of pomegranate peel extract significantly increased the activity of SOD, GPx, and TAC enzymes, while the MDA level decreased compared to the group treated with cadmium (p<0.05). Therefore, it seems that the use of pomegranate peel extract as a feed supplement can be useful to mitigate the effects of experimental poisoning caused by cadmium in common carp, although more studies are needed in this field.

According to the importance of macrozooplankton in food chain, this study was conducted with the aim of investigating the abundance and diversity of macrozooplankton in the coastal waters of Khuzestan and Bushehr provinces in the winter of 2021. For this purpose, 11 stations were sampled using 300 micrometers mesh size plankton net equipped with a flowmeter in the middle third of the net opening between the center and the edge of the net. In total, 2537.509±5.85 number per m2 of zooplankton belonging to 51 species, 27 genera, 29 families, 13 orders, 12 classes, and 5 phylum of zooplanktons were identified and counted. Arthropods phylum in the coastal waters of Khuzestan and Bushehr provinces was the predominant macrozooplankton phylum with 99.56% and 98.91%, respectively. No significant difference was observed between the coastal waters of the two mentioned provinces in the abundance and diversity of macrozooplankton (p>0.05), which can be caused by the similarity of the characteristics of the sampled areas and the homogeneity of the environment. However, there was a significant difference in the abundance of macrozooplankton among the investigated stations in each province (p<0.05), which is caused by the influence of environmental and nutritional conditions. The lower level of the Shannon and margalef indices in Khuzestan province indicates more stress in the region. Therefore, it is necessary to continuously monitoring and measuring environmental factors and pollutants in the coastal waters of Khuzestan and Bushehr provinces for four seasons to determine the most important factor of stress.

In this research, the frequency of coral fishes from Hengam Island were studied seasonally from summer of 2020 to the spring of 2021 by Underwater Visual Census (UVCm) and belt transect method. A total of 38 species were identified in five selected stations, of which 31 species were herbivorous fishes,  Pomacentridae and Labridae families had the highest frequency with 7 and 4 species. The abundance of herbivorous fish Thalassoma lunare was estimated at 80(±71) number per square kilometer in station two. In addition, two species of parrotfish (Scarus persicus and Scarus ghobban) were the most frequent in all stations. The highest seasonal frequency of herbivorous fishes was recorded at station 2 in winter 58(±12) numbers per square kilometer and the lowest at station 3 in summer 5(±21) numbers per square kilometer. The seasonal abundance of herbivorous fishes were significantly differ between stations, except in summer (p<0.05). The temporal and spatial changes in the abundance of herbivorous fish in the stations indicate the importance of selective performance of fishes for ecological niche. In this regard, the role of functional redundancy is more effective than the role of functional complement among these fishes in the biological future of the coral communities of Hengam Island. Therefore, it is recommended to protect the coral fish stock of the island.