فصلنامه تغذیه آبزیان
سال دوم شماره 1 (پیاپی 3، بهار و تابستان 1395)

This work was conducted to study the fatty acid profile of oil extracted from rainbow trout by-product by isoelectric solubilization/precipitation and its oxidation stability during 45 days refrigerated storage. After extraction and methylation of extracted oil, fatty acid profile was determined by gas liquid chromatography. Free fatty acid, peroxide value and thiobarbituric acid were measured in 15-day intervals to determine the hydrolytic and oxidation stability during 45 days. Twenty three fatty acids were identified in acidic, basic and control samples. Extraction of oil by acidic and basic Isoelectric solubilization/precipitation affected neither the fatty acid profile nor the content of ling chain fatty acids. n-3/ n-6 ratio were 0.148 and 0.172 in acidic and basic treatments, respectively. Atherogenic index and thrombogenic index in acidic and basic treatments were found to be 0.223 and 0.380, as well as 0.202 and 0.347, respectively. The extracted oils were stable to oxidation during 45-day storage in refrigerator.

Beluga (Huso huso) larvae with average body weight of 30.43 ± 1.25 mg and density of 2 fish per liter having three replicates (100 fish per tank) were fed on the 30 percentage of body weight in a day during 15 days using Daphnia magna, Artemia urmiana nauplii and mix of Artemia and Daphnia magna, Artemia urmiana nauplii and the mix of them (Daphnia 50% w/w and Artemia 50% w/w) in a completely randomized design. The fish was weighed individually at the start and the end of the experiment. The carcass proximate compositions of samples of fish were determined. The maximum of carcass crude protein (76.70%) and lipid (8.83%) was obtained in treatments of Artemia and showed significantly difference with treatment of Daphnia and mix of Artemia and Daphnia, respectively (P<0.05). Thesignificant difference in protein, lipid and energy productive value were observed among the treatments (P<0.05). The highest energy retained as protein (13.76 J/day) and lipid (45.14 J/day) were observed in treatment of Daphnia. The best final body weight (193.98) and feed conversion ratio of 2.80 were observed in treatment of Daphnia. The maximum specific growth rate in protein (SGRP), lipid (SGRl) and energy (SGRe) were obtained in fish that fed on Daphnia. The results of this experiment showed that the potential of Huso huso larvae in using of Daphnia magna, Artemia urmiana nauplii and mixture of them was different and Daphnia had a suitable effect on promotion of feeding parameters in larval stage.

This study was conducted to investigate the growth pattern and ontogeny of the activity of alpha amylase enzyme in common bream (Abramis brama) from hatching through 60th day post hatching (dph) at the Shahid Ansari breeding and restocking center (Rasht, Guilan, Iran). The results showed that wet weight and total length of common bream were 0.65 ± 0.03 mg and 4.66 ± 0.24 mm at hatching, respectively. The growth pattern from early development through 60th dph was exponential as Y = 5.9558e0.0346xand R² = 0.97. The results also revealed that alpha- amylase enzyme was present at the hatching and its activity was constant till 4th dph and had an increasing trend till 25th dph. Then, a significant decrease was observed in the activity of this enzyme on 35th dph; thereafter its activity showed an increasing trend till 60th dph. In addition, the activity of alpha-amylase showed a strong relationship with increasing the age of specimens. The results also revealed that ontogeny of the alpha-amylase in common bream larvae are similar to that of other omnivorous and herbivorous fishes. It can be concluded that the food with higher content of carbohydrate can be used after 12th dph for feeding of their larvae.

The analysis of blood parameters is a useful indicator in assessing the physiological conditions of aquatic animals in response to stress, pollutants, nutrition, and also physiological and ecological changes. In this study, some hematological parameters of Acipenser persicus in three age classes including cultured fingerlings, juveniles and broodstocks were studied in a six-month period (spring and summer 2012). The counts of red blood cells (RBC), white blood cells (WBC), hematocrit (PCV), hemoglobin (Hb), MCV, MCH, MCHC, electrolyte and non-electrolyte biochemical parameters, and also differential leucocyte count were measured in different age classes. For this reason, 30 Persian sturgeon(10 fingerlings, 10 juveniles, 5 males and 5 females) were used. Statistical results showed significant differences in Hb, RBC, MCV, MCHC, WBC, lymphocyte (%), neutrophil (%) and eosinophil (%) in different age classes of this species (P<0.05). There were significant differences in non-electrolyte biochemical parameters such as glucose, albumin, total protein, triglyceride, cholesterol, osmolality and total lipid at different ages (P<0.05). Significant differences were observed in electrolyte biochemical parameters including sodium and chloride ions at different age classes and also at females and males. It was also true for calcium and potassium ions at different ages (P<0.05). Based on the results, it can be concluded that the hematological and biochemical parameters are affected by age and sex of fish although the effects of environmental and nutritional parameters are inevitable.

Effects of vitamins C and E - supplemented diet on hematological indices of rainbow trout Oncorhynchus mykiss juveniles at two different densities were investigated in a 6-week trial. Rainbow trout juveniles (initial body weight of 9.6 ± 0. 69 g) at two stocking densities of 50 and 100 fish per 50 liters were fed three diets containing the same level of protein and fat, but with different levels of the vitamins. Experimental diets included diet 1 without vitamins, diet 2 supplemented with 1500 mg/kg vitamin C and diet 3 with 600 mg/kg vitamin E. A total number of 1350 rainbow trout juveniles were devided in six treatments each with three replicates as T50(0) (density = 50, fed diet 1), T100(0) (density = 100, fed diet 1), T50(C) (density = 50, diet 2), T100(C) (density = 100, diet 2), T50(E) (density = 100, diet 3) and T100(E) (density = 100 diet 3). After a 6-week feeding, hemoglobin level, the number of red blood cells and sodium level were significantly higher in T100 treatments (P<0.05). Plasma glucose and cortisol were also significantly higher in T100 treatments (the highest in T100(0)) than in T50 treatments (the highest in T50(0)) (P<0.05). T50 treatments had higher levels of blood albumin and total protein (P<0.05). There were no significant differences in number of white blood cells and potassium level between treatments (P>0.05). According to the results, supplementing the diet of rainbow trout with vitamins C and E enhances fish resistance to the stressful environment caused by stocking density.

Nowadays, importance of storage and marketing of fresh fish, with regard to consumer prefer for fresh fish rather than frozen fish is increasing. So, determination of fish shelf-life, to find its storage time, due to high perishability of fish, is important. This study was aimed to investigate the process of spoiling changes and determining the shelf-life of silver carp fillet during storage period in refrigerator (at 4ºC). For this purpose, silver carp fillets were kept in refrigerator for 16 days and the changes of peroxide value, tiobarbitoric acid (TBA), total volatile bases nitrogen (TVB-N), total plate count (TVC), Psychrophilic bacteria (PTC) and sensory evaluations were assessed. The results showed that the quantity of chemical indices increased during storage period. According to these results, Silver carp fillet can be kept in refrigerator for 6 days.