نشریه علوم و فنون شیلات
سال هشتم شماره 3 (پیاپی 27، تابستان 1398)

The present study was conducted to determine the exotic fish food strategy of rainbow trout escaped from cultivating cages located in the coast of Mazandaran.

A total of 90 specimens of this species were collected during the period from September 2017 to May 2018 from bony fish from west to central coast of Mazandaran. Samples were biomediated and the age was determined by scales.

The relative frequency of food items were Balanus glandula, Clupeonella cultriventris, Cerastoderma lamarcki, Neogobius fluviatilis, Atherina caspia, Chelon saliens, Chinavia hilaris, Taxiphyllum barbieri, Rutilus kutum, Cumacea, Syngnathus caspius and Gasterosreus aculeatus, respectively. The result showed that a wide range of food was more central than the west, the fullness index in the female was more than male and in age groups older than 2 and 3 is more than 1 (p>0.05). The fullness index, especially in the spring, increased significantly, the presence of B. glandula more than C. cultriventris, but its relative importance was less than C. cultriventris (p> 0.05).

This fish has a carnivorous behavior and uses a wide range of foods, so it is possible to compete with many species of Caspian Sea fish such as Salmo caspius. The effects of the adaptations and behavioral, physiological and ecological mechanisms, C. cultriventri and B. glandula were more important in fish feeding.

Fish is a potential source of vitamins and minerals and the cooking method play an important role in the final content of nutrients of it. The aim of the present study was to the effects of different cooking methods on the heavy metals, fillet proximate composition and fatty acid composition of Roach (Rutilus rutilus) fillet.

Four cooking methods such as deep frying, baking, steaming, and microwave cooking were applied on the fillet. Determination of the remaining heavy metals of the samples was carried out using atomic absorption. The proximate composition was assessed using the standard methods. To measure the composition of fatty acids, Gas Chromatography method (GC) was applied.

All treated samples had a significant decrease in moisture (frying) and ash (microwave) and a significant increase in fat (frying) and protein (baking). The polyunsaturated fatty acids (PUFA), ω‐3 fatty acids as well as EPA/DHA content increased in baked samples in comparison to raw fish fillets and other cooked. The frying process caused a significant increase in lead concentration content. While the steaming significantly decreased heavy metals concentration in comparison to raw fish fillets and other cooked.

Considering the increasing of EPA, DHA, and ω‐3/ω‐6 ratio in baked‐cooked and losses of heavy metals in steamed, these two cooking methods are the best cooking method for this type of fish and healthy diet.

The present study investigated the effects of different levels using of mealworm (Tenebrio molitor L., TM) on the growth and feed performance, body composition and digestive enzymes of rainbow trout, Oncorhynchus mykiss.

Fish (8.58± 0.27 g) in a completely randomized design in 4 treatments and each with 3 replications. Rainbow trout with different levels of 0, 15, 30 and 60% diet (TM0, TM15, TM30 and TM60) (including 50% moisture) of live worm for 30 days. Data were analyzed by one-way (SPSS 17). When p values were significant (P<0.05), means were compared using Duncan's multiple-range test.

At the end of the experimental, there were significant difference between treatments in growth performance and feed utilization. The results revealed that fish growth parameters and efficiency of nutrient utilization tended to increase with increasing dietary TM levels from 0 to 60%. Feed Conversion Ratio (FCR) was significantly reduced in fish fed the diet with the highest worm level (TM60). The treatments fed TM showed highest protein and lower lipid content compared to fish fed control diet. The analysis of gastrointestinal enzymes showed that amylase, protease and lipase had a statistically significant difference between the control and other treatments. Protease and amylase activities were found to be significantly higher for fish fed the TM60 diet compared with fish fed TM0 diet.

The results showed that using 60% (TM60) of worm instead of the base diet can improve growth, carcass composition and digestive enzymes.

In this study, for the first time in Iran, the effect of edible coating of sodium alginate and whey protein in combination with innclulated cultivation of Pediococcus acidilactici and Lactobacillus plantarum bacteria on rainbow trout fillets was studied. Accordingly, chemical indicators such as pH, TVB-N, TBA and microbial laod at 0, 7, 14 and 21 days of refrigeration storage at 4C were investigated. Results showed that in all samples pH, TVB-N and TBA increased over time. In terms of microbial parameters, probiotic coating could reduce the number of TVC in coated fillets on day 21 compared to control treatment. However, the TVC level in all treatments at the end of the storage period was higher than the allowable range for human consumption (P<0.05).  The number of LAB also increased during the storage period and there was a significant difference in coated treatments compared to control (P<0.05).  The highest changes were observed in control treatment and the lowest changes were related the coated treatments. Overall, using higher percentages of sodium alginate containing probiotic bacteria can be recommended for better preservation of the fillet during the refrigerated storage.

The aim of the present study was to extract gelatin from the skin of farmed great sturgeon at different temperatures, hydrolysis using Alcalase enzyme, and to measure molecular weight distribution of peptides, amino acid composition and antioxidant activity of hydrolysates.

After removing pigments and non‐collagenous proteins, defatting, and swelling of triple‐helix structure, gelatin was extracted at the temperatures of 50, 60, 70, and 80°C for 6h and then hydrolysed using Alcalase (E/S ratio of 1:20w/w) for 3h. Molecular weight distribution of peptides, amino acid composition and antioxidant activity of hydrolysates were determined in different models.

Degree of hydrolysis (DH) reached its maximum within the first 30min in all samples. The highest DH was in the 80°C. There were no significant differences among hydrolysates with regards to amino acid composition and peptide molecular weight distribution. Hydrolysates produced at the extraction temperature of 60°C showed that the content of small peptides (molecular weight<1kDa) and total amino acids (g/100g) were slightly higher compared to other samples. This could influence antioxidant activity. At higher extraction temperature of gelatin, the efficacy of hydrolysates in preventing the loss in total sulfhydryl groups content was decreased (p<0.05) while there was no effect on TBARS and surface hydrophobicity (p<0.05).

Extraction temperature of gelatin did not reveal a considerable effect on properties and antioxidant activities of the resulting hydrolysates and gelatin hydrolysates with antioxidant activity and rich in peptides with molecular weight less than 1kDa could be produced at 50°C.

This research aimed to evaluate the spatial patterns of water quality and its controlling factors in the Mazandaran coastal ecosystem during winter using the multivariate analysis methods.

Water quality parameters such as nutrients, temperature, conductivity, salinity, DO, pH, chlorophyll-a and turbidity were measured monthly in 16 stations (44 layers) along 4 transects (Amirabad, Babolsar, Noushahr and Ramsar). To evaluate the data, several multivariate statistical methods were used including discriminant function analysis, cluster and factor analysis as well as correlation test.

Results of cluster analysis showed that the sampling sites (44 layers) were classified into 4 groups. Based on discriminant analysis, 93.20% of the sampling sites correctly classified. Factor analysis extracted 4 principal components that explained 74.05% of the total variance. Based on these analyses, organic phosphorus, organic nitrogen, turbidity, chlorophyll-a and temperature were the most effective parameters on the spatial variation of water quality.

This study suggested that the number of sampling locations could be reduced to 3 transects including Amirabad, Babolsar and west coasts (Noushahr and Ramsar) and 2 stations (one surface layer and one deep layer). Transport of nutrients from land, sea floor and fish cage culture were the most effective factors on spatial patterns of water quality in Mazandaran coasts. Based on the results, multivariate statistical methods are also introduced as one of the useful methods for identifying the spatial pattern of water quality.

The aim of the current study was to determine the role of Avicennia marina’s primary production as well as other food sources in the diet of Longjaw thryssa, Thryssa setirostris (Broussonet, 1782) in an arid mangrove ecosystem using carbon stable isotopes of carbon (δ13C) and nitrogen (δ15N).

We collected five potential food sources in the ecosystem including fresh and senescent leaves of Avicennia marina, particulate organic matter, microphytobenthos and sediment organic matter for further stable isotope analysis. Additionally, fishes were collected with a combination of set nets and seines. The muscle tissue (boneless and skinned, 5 g) was removed from the dorsum of fish.

Significant differences were found between carbon and nitrogen isotopes of different food sources (p < 0.05). Although, this was not significant for green and senescent leaves (p > 0.05). The average values of carbon and nitrogen isotopic ratios of T. setirostris were 15.93‰ and 13.01‰, respectively. The SIMMR model showed that the contribution of senescent and fresh leaves in the diet of T. setirostris was 15% and 10%, respectively.

The result of the current study emphasized a limited role for mangrove detritus in the diet of transient fishes in an arid mangrove ecosystem.