نشریه علوم و فنون شیلات
سال یازدهم شماره 3 (پیاپی 39، تابستان 1401)

This experiment evaluated the effect of soluble polysaccharides in Spirulina platensis microalgae on growth performance, body composition and immune response of rainbow trout (Oncorhynchus mykiss). In this regard, 180 rainbow trout (17.22 ± 0.5g) were selected and distributed in five experimental treatments (with three replications). Treatments included different levels of polysaccharide in dosage of 0 (control), 500, 1000, 2000 and 3000 mg / kg of feed. According to the results, in growth factors (final weight, body weight gain, specific growth factor, protein efficiency, feed conversion ratio and condition factor), no significant difference was observed. The highest and the lowest amount of carcass proteins were observed in the diet containing 500 mg polysaccharide and control, which showed a significant difference. The amount of fatty acids of the muscle of the fish body did not show any significant difference among the treatments. The highest and lowest levels of lysozyme activity were observed in treatments of 2,000 mg polysaccharide and control and the highest and lowest levels of complement activity were observed in treatments containing 3000 mg polysaccharide and control respectively (P <0.05). In general, the use of polysaccharide extracted from micro-algae did not significantly improve rainbow trout growth, but a slight improvement in growth and body composition (protein) in 500 mg polysaccharide per kg of diet was observed. In terms of safety indicators, treatments of 2,000 and 3,000 mg of polysaccharides per kg of diet had a good performance and could be used whenever needed.

Chl a is the main pigment of phytoplankton, which is an indicator of phytoplankton biomass and reflects the primary production in the marine environment. In this study, level 3 (4 km) data of Chl a concentration of Persian Gulf and Oman Sea for the period of 2003- 2018 were used. The data was converted to raster format in ArcGIS10.5 environment and then the numerical values of each pixel were extracted in R (version 4.0.2). Missing data were observed in Chl a data, to solve this problem, DINEOF algorithm was applied and non-parametric Mann-Kendall and Sen’s Stimulator tests were used to analyze Chl a concentration trends. The results showed that the maximum concentration of Chl a is in September (0.09 to 18.75 mg / m3) and October (0.23 to 18.03 mg / m3) and the minimum concentration of Chl a in May (0.22 to 5.74 mg / m3) and June (0.20 to 5.12 mg / m3). The trend of Chl a concentration variability over the study period was negative in most areas and not significant. These analyses provide an overall description of Chl a concentration variability in the Persian Gulf and Oman Sea based on satellite observations; however, further investigations based on in situ observations are needed to achieve better understanding of the patterns of of Chl a concentration alterations.

Today, due to the confirmation of the existence of polyphenolic compounds with antioxidant properties in pomegranate peel, the study of its application potential in food health and fishery products has been the focus of researchers. In the present study, the effects of oral administration of ethanolic extract of pomegranate peel (Punica granatum L.) (Dose: 600 mg/kg) on functional changes of antioxidant system and biochemical parameters of blood serum of common carp (Cyprinus carpio) during a 45-day exposure against stocking density stress was monitored. In this regard, fish were randomly divided into 6 groups (3 treatment groups and 3 control groups with different levels of stocking density (3, 5, and 10 kg / m3) and three replications. At the end of the exposure period, fish bloodletting and serum preparation were performed. The results of this study did not show a significant increase in biochemical parameters (phosphorus, chlorine, magnesium, calcium, and triglycerides) as well as the activity level of some enzymes and antioxidant compounds such as SOD and MDA in fish serum compared to the control group. However, for stress indicators such as glucose and cholesterol and antioxidant activity such as CAT and GSH, production level has been significant. According to the findings, oral administration of pomegranate peel extract dietary supplement is recommended for consumption in dense aquaculture centers of common carp fish.

This study was carried out after receiving a report of the mortality of Sterlet sturgeon (Acipenser ruthenus) juveniles from a fish farm in Sari-Mazandaran in April 2021 to isolate and identify the pathogen in the ill Sterlet sturgeon (A. ruthenus)  juveniles. Sampling was performed from 20 ill Sterlet (A. ruthenus) juveniles. Clinical symptoms were recorded, followed by autopsy, kidney, and liver tissue sampling, bacterial culture, biochemical tests, anti-biogram test, DNA isolation, and 16Sr RNA gene sequencing. The tested isolate with 1418 base pairs (bp) was identified as a non-motile strain of A. veronii bacteria. It was registered in the World Gene Bank (NCBI) under the name Aeromonas veronii TMU000126. This strain of bacterium showed sensitivity to the Florfenicol as well as, resistance to Trimethoprim-sulfamethoxazole, Oxytetracycline, Doxycycline, and Fosfomycin antibiotics. The results revealed that the non-motile strain of A. veronii, like its motile strain, was the cause of disease and mortality in Sterlet sturgeon (A. ruthenus). According to the available studies, this study might be considered the first study on the disease of the sturgeon species of Sterlet (A. ruthenus), and the pathogenicity of the non-motile strain of A. veronii species.

Biofloc technology is considered as a culture system for fish production reduced environmental impacts. In the present study investigated the impact of zeolite nanoparticle on water quality, growth performance, digestive enzymes and immune response of common carp (Cyprinus carpio) reared under biofloc conditions. Fish fingerlings (initial weight of 7.99 ± 0.36 g) were divided into four treatments and fed four levels of zeolite nanoparticles in the following 0 (control), 50, 100 and 200  mg kg−1 diet in biofloc system (NZ1, NZ2 and NZ3) for 60 days. Carbon to nitrogen ratio (15:1) was provided using sucrose. Water quality parameters such as nitrogen compounds were measured during the test period. At the end of the experiment, the highest growth indices and the lowest feed conversion ratio were obtained in 50 mg kg−1 diet (NZ1). Intestinal protease activities in NZ1 and NZ2 treatments were significantly higher than in the other treatments, and the highest lipase and amylase activity was related to the NZ1 treatment. The 50 and 100 Zeolite diets in biofloc conditions significantly enhanced fish immune system activity. The present study suggests that dietary supplementation with 50 and 100 mg Zeolite nanoparticles in biofloc system significantly increases growth performance, digestive enzyme, and immunological response in common carp in fish culture tanks.

Estimation of coral fishes biomass is needed as a basic benchmark for assessing the ecological status and fishing potential of coral reefs. Different methods are used to sampling the biomass of these communities, that direct observation is one of the preferred methods with respect to the non-destructive advantage. The purpose of investigation was to estimation standing biomass of coral fishes by Underwater Visual Census method (UVCm) in Abu-Musa Island seasonally from October 2019 to September 2020. also confidence interval was calculated of these estimations from the bootstrapping test (95%). Standing biomass of Coral fish and their confidence interval (95%) by bootstrapping simulation (n=479) were determinated 2923.6 kg., 4576.2 kg, and 1645.4 kg for the stations one, two and three respectively. The difference in the biomass standing of coral fish in three station could be related to the lack of differences in the amount of developed reefs, coral communities and significant differences in habitat availability.  Also, the standing biomass of coral fishes in the Abu-Musa Island are limited, that can be attributed to their low habitat, shortage of carrying capacity and the short life of the Persian Gulf basin, and stress that occurs in the ecosystem, especially bleaching events, that need more study in the future.

A recirculating hatchery system (RHS) and a flow-through system (FTS) in terms of major macro elements (Ca, Mg, Na and k), some microelements (Fe and Cu), total bacteria and quality characteristics of Rainbow trout eggs and larvae were comparatively studied. A recirculating system (RHS) and a flow-through system (FTS) were designed for incubating the eggs and rearing the yolk-sac larvae. Fertilized eggs were distributed (5000 eggs in each tray) in four replicates and incubated under the standard conditions until yolk sac absorption. Total bacteria and macro/micro elements were measured at one-week interval. Eyed egg percentage, hatching rate, growth, and survival rate of larvae were measured. In the FTS and RHS, percentages of the eyed eggs were 79.75% and 79.01% respectively, and hatching rates were 70.31% and 63.65%, respectively. There were no significant differences amongst the values of Ca, Mg, and Na during the experimental period and between two systems. K Values in the RHS were significantly higher than in the FTS during the egg incubation period. Fe Values in the RHS were more than in the FTS, and increased during the study period in both systems. The values of total bacteria in the RHS were significantly higher than in the FTS.  Despite the differences observed between the experimental systems, the designed RHS can be used for incubating the eggs and rearing the yolk-sac larvae in rainbow trout hatcheries, because of its simplicity, low water consumption, and acceptable efficiency.