فصلنامه تغذیه آبزیان
سال هشتم شماره 3 (پیاپی 21، پاییز 1401)

The purpose of this study was to evaluate the effects of Lactobacillus acidophilus and Candida utilis probiotics on mucus immunity, growth indices and liver enzymes of common carp (Cyprinus carpio). This study was in the form of a completely randomized design with 4 treatments and 3 repetitions including: 1- basic diet, 2- basic diet + bacteria (1.23 g), 3- basic diet + yeast (0.67 g) and 4- basic ration + bacteria (0.625 g) and yeast (0.333 g) per kg of diet in 60 days. A number of 300 fish with an average weight of 12 ± 0.33 g were randomly distributed in 12 tanks (300 L) with a density of 25 fish in each tank. Based on the results, no significant difference was observed in terms of growth indices between the treatments except for the protein efficiency ratio (p>0.05). However, significant differences were found between the treatments (p<0.05) in terms of mucus immune parameters, lysozyme activity, total immunoglobulin and total protein. It was also true for AST and ALP which exhibited significant differences between the treatments (p<0.05). Based on the general results of this study, using Lactobacillus acidophilus and Candida utilis as probiotics displayed the highest enhancement on the fish immune system.

The amount of lysine required in the diet of juvenile Beluga Huso huso with an average initial weight of 2.45 g was evaluated based on growth response in 12 aerated aquariums in four treatments each with three replications for 40 days. Four diets were prepared based on fish meal with the same protein (39.32%), fat (15.78%) and carbohydrate (21.19%) with different levels of lysine (0, 0.75, 1.5 and 2.25% of dry weight). The diet without lysine was considered as the control diet. Each ration was given in proportion to 4% of body weight, in three equal portions, to groups of three with 10 fish in each replicate. The mean water temperature, dissolved oxygen and pH during the test period were 23.8 ºC, 6.27 mg/L and 7.32, respectively. The results showed a significant difference in the growth performance between the treatments. The maximum weight obtained (31.95 ± 0.84 g) and specific growth rate (7.01 ± 0.09%/day) were observed in the treatment with 2.25% lysine. Apart from the decreased growth in the fish fed the lysine-deficient diet, no signs of growth deficiency were observed in the other fish. Codition factor, food conversion ratio, protein efficiency ratio and survival rate were not significantly different among treatments. Finally, the optimal amount of lysine for this weight group of juvenile Beluga was estimated to be 2.25 g per 100 g of the dry weight of the diet.

In this study, gelatin was extracted from the by-product of Scomberoides commersonnianus, and after evaluating its characteristics, a biodegradable film was prepared from the gelatin. The results showed that the yield of extracting gelatin, pH and hardness were 12%, 5, and 100 grams, respectively. The gelation time and temperature were 18°C in 175 seconds. Evaluation of the mechanical properties of the edible film based on fish gelatin showed that the tensile strength and elongation at the break point were 3.6 MPa and 27.2%, respectively. The physical properties of thickness, humidity, solubility, and water vapor permeability were reported as 0.08 mm, 5.2%, 21.3%, and 5.8 g mm/h mm2kpa × 10-6, respectively. SEM images showed a smooth structure without pores. Moreover, gelatin film did not show antibacterial properties against E. coli, Staphylococcus aureus, Bacillus subtilis, and Bacillus cereus. However, based on the results of the fish gelatin film can be introduced as a suitable candidate for the preparation of composite films with other biopolymers, and the addition of antibacterial compounds can improve their antibacterial property.

One of the limitations in fish reproduction is the duration of sperm motility. One of the hypotheses related is the possibility that sperm survive relatively long in the female body. Therefore, in this study, the reproductive ability of koi carp (Cyprinus carpio var. Koi fish) was investigated by direct injection of sperm into the female ovaries. Three experimental groups were investigated in this study. In the control group, fertilization was performed by the conventional method. In the second group, sperm was injected directly into the ovaries 12 hours before ovulation, and in the third group, sperm were injected 2 hours before ovulation. In each group, 2 males and 3 females were used. Fertilization was performed by the dry fertilization method, using a mixture of cow's milk and water in a 1:10 ratio to eliminate adhesion. The results showed that in groups 2 and 3, which were injected directly into the ovary 2 and 12 hours before ovulation, respectively, the percentage of fertilization did not show a significant difference (p<0.05), but the percentage of fertilization in the control group was significantly (p<0.05) higher than groups 2 and 3. The percentage of hatching and survival showed no significant difference between control group and groups 2 and 3 (p<0.05). The results showed that ovarian fluid in carp could not activate sperm for motility. In general, it can be said koi carp sperm can maintain their fertilization ability in the ovaries of female for at least 12 hours.

The present study was designed and implemented to evaluate the effects of relative replacement of different levels of dehulled soybean meal (DHSM) instead of fish meal on growth performance of adult Persian sturgeon (Acipenser persicus). In this study, a total of eighty 4-year-old Persian sturgeons (Acipenser persicus), with an average weight of 3850 g were fed with 8 isonitrogenetic and isolipidic diets for 52 weeks. Experimental diets include different percentages of dehulled soybean meal include 0, 10, 15, 20% without amino acid, 15 and 20% replacement with lysine and methionine, and 15 and 20% replacement with lysine and methionine and L-carnitine supplement (DHSM0, DHSM10, DHSM15, DHSM20, DHSM20+AA, DHSM15+AA, DHSM20+AA+L.car. DHSM15+ AA+L.car.). After 52 weeks, no significant difference was observed between weight gain (WG), specific growth rate (SGR), LX and PV in different treatments. The protein efficiency ratio and feed efficiency (FE) in DHSM0 was significantly higher than that of DHSM20+AA and DHSM15+AA. Hepatosotic index of fish in DHSM0, DHSM10, DHSM15, DHSM20 + AA+L.car. DHSM30 + AA+L.car. was significantly higher than that in DHSM30 + AA. Gonadosomatic index exhibited alterations under the influence of the diet.  Effect of diets containing dehulled soybean meal with L-carnitine supplement on the reproductive system of female fish was significant and positive. The somatic growth in female Persian sturgeon was higher than that of males. However, their gonadic growth and stages of sexual maturity were significantly lower than that in males. The highest sexual maturity index of male fish was observed in DHSM15 + AA+L.car diet, so that at the end of the rearing period, 75% of fish were in stage IV of sexual maturity and 25% in stage III-IV. Addition of L-carnitine and essential amino acid supplement such as lysine and methionine to the diet containing soybean meal displayed a positive effect on the growth and reproductive indicators in the functional diet of Persian sturgeon and probably can improve significantly the production of Persian sturgeon fry.

Oxygen concentration is known as one of the limiting factors in aquaculture production. The present study aimed to evaluate the effects of vitamin E and zinc (Zn) on the metabolic rate and some growth indices in common carp Cyprinus carpio exposed to chronic low oxygen levels. So, 495 fingerling fish with an average weight of 15.38 ± 1.23 g were randomly selected and divided into two independent groups and fed with diets containing different amounts of vitamin E and Zn for 8 weeks. The vitamin E and Zn (E:Zn) concentrations were 0:0, 60:0, 0:20, 60:20 mg/kg for the control groups (C1-C4) and 0:0, 60:0, 0:20, 60:20, 0:40, 120:0 and 120:40 mg/kg for the treatment groups (T1-T4), respectively. All the physicochemical parameters of water except oxygen were the same for both control and treatment groups. Oxygen concentration for the control and the treatment groups were 8.7 ± 0.43 and 4.1 ± 0.38 mg/L, respectively. Chronic hypoxia led to a significant decrease in growth indices such as final weight and body length (p<0.05). In addition, the level of fish basic metabolic rate and maximum fish metabolic rate, aerobic metabolism scope in chronic hypoxia conditions were significantly lower than the control group (p<0.05). Nevertheless, using dietary supplements in the fish diet led to a significant improvement in the examined parameters in the treatment groups (p<0.05). The results of the present study showed that using food supplements, in addition to improving the metabolic rate of fish under chronic hypoxia condition, lead to an elevated efficiency of feeding and growth, which is directly related to the production efficiency of aquaculture systems.