فصلنامه تغذیه آبزیان
سال هشتم شماره 1 (پیاپی 19، بهار 1401)

Probiotics as alternatives to chemicals and antibiotics have proven to be effective in promoting successful aquaculture. They can improve water quality, increase tolerance to stress, generate high-quality livestock, etc. The present study aimed to investigate the effect of adding Lactobacillus rhamnosus PTCC 1637 to water on the intestinal tissue of rainbow trout, Oncorhynchus mykiss. This experiment was performed in three treatments including 1: days 1 to 7; 2: days 1 to 20; and 3: days 1 to 60, by adding the bacterium at 106-107 CFU/mL into the water and also a control group. The above mentioned concentrations of the bacterium in group 1 were added on days 1, 3, and 5; in group 2, at every two days; and in group 3, from 1 to 20 on every other day, then from 20 to 60, once in four days. At the end of the experiment, intestinal alteration was examined. The results showed that the highest length (247.2 µm) and width of intestinal villi (70.6 µm) were related to the hatched egg group from 1 to 60 days (hatched egg part), while the lowest in the control group. There was no significant difference between the average width and length of the intestinal villi in other treatments compared to the control group. In general, the use of bacteria in the eyed eggs group (days 1 to 60 at a concentration of 107 CFU/mL) showed a more favorable result than in the alevin and fry groups. Finally, the direct addition of probiotics to the water effectively improved intestinal morphology in O. mykiss.

In the present study, the effects of probiotic (0 and 1) in rainbow trout fed with different levels of soybean meal (SBM; 0, 20 and 40%) were evaluated on hematological and immune indices. A total of 300 fry with average initial weight of 20.05 ± 0.20 g by density of 25 fish per tank assigned to 12 tanks for 90 days. Blood was taken from fish on days 0, 45 and 90, afterward hematological and immune indices were estimated. According to hematological results in day 45, fish fed with SBM 0 demonstrated greatest number of white blood cells and hematocrit among treatments (p < 0.05). In day 90, the highest number of red blood cells was found in SBM 0 and SBM 20% containing probiotic (p < 0.05). Number of white blood cells significantly increased by adding probiotic to different SBM levels (p < 0.05). Hematocrit and hemoglobin concentrations decreased in fish fed with SBM 40% (p < 0.05). In addition, there were interaction between SBM × probiotic in white blood cells on day 90 (p < 0.05). According to immunological results in day 45, neutrophil burst activity (NBT) was elevated by adding probiotic to SBM levels (p < 0.05). The IgM and C3 levels were significantly enhanced by adding probiotic to SBM 0 and SBM 20%. In day 90, the highest NBT value was observed in SBM 0 (probiotic 0 and 1) and SBM 20% containing probiotic among groups (p < 0.05). Addition of probiotic to SBM 0 and SBM 20% caused the elevated lysozyme, IgM, C3 and C4 values (p < 0.05). Furthermore, interaction between SBM levels and probiotic indicated significant effects on NBT after 90 days (p < 0.05). It could be revealed from the current study that L. plantarum compensated some adverse effects of SBM replacement on blood and immune indices by enhancing immunity, hence higher replacement of SBM is not suggested without using probiotic.

This study was performed to evaluate the effects of two types of powdered extract Echinacea purpurea and Allium sativum on growth indices and survival rate of Huso huso during a two-month period. For this purpose, 210 juvenile with an average weight of 27.74 ± 0.26 g were randomly placed in 21 half-ton fiberglass tanks in seven different treatments with three replications, including a control group and three experimental groups of different amounts of E. purpurea powder extract (T1, T2 and T3: 250, 500 and 1000 mg kg-1) and three experimental groups of different amounts of garlic powder extract (T4, T5 and T6: 250, 500 and 1000 mg kg-1). At the end of the experiment, a statistically significant difference was observed between the treatments in the mean final weight, mean final length, final biomass, final production, fish weight gain, mean daily growth, body weight gain increase, specific growth rate and daily growth rate (p<0.05). These indices in the treatments had an increasing trend compared to the control and in T6 (1000 mg of E. purpurea powder extract per kg of food) which was significantly higher than in the other treatments (p<0.05). The feed conversion ratio in this treatment was also decreased significantly compared to other treatments (p<0.05). There was a significant difference in levels of ALP and LDH enzymes between treatments and control group (p<0.05). The highest level of ALP enzyme was in control group and T6, while the lowest level was in T4 (250 mg of E. purpurea powder extract per kg of food) (p<0.05). The highest level of LDH enzyme was observed in the control group and T6, however, the levels of ALT and AST enzymes were not significantly different between treatments and control group (p>0.05). The results showed that addition of 1000 mg turmeric powder extract per kg of food is more effective in improving growth indices.

Biofloc technology is a technique to maintain water quality by absorbing water nitrogen and converting it into the microbial protein. The purpose of this study was to investigate the effects of adding Nannochloropsis oculata and Isochrysis galbana on biochemical composition of biofloc and Nile tilapia (Oreochromis niloticus) fillet. This study was carried out using 5 treatments including control (T1), biofloc group (T2), treatments containing biofloc and N. oculata (T3), biofloc and I. galbana (T4), and biofloc and combination of both algae (T5) on Nile tilapia with a density of 15 fish per tank (with water intake volume of 150 liters) and in the system without water exchange in a period of 60 days. According to the results, the highest values of fish fillet fat were obtained in the treatments containing biofloc (p<0.05). No significant difference was observed in the dry weight and carcass protein values among the treatments containing biofloc (p>0.05); however, significantly highest compared to the control (p<0.05). The amount of ash did not show a significant difference among experimental treatments (p>0.05). Also, the highest amount of carbohydrates was observed in the control group (p<0.05). Based on organoleptic properties of tilapia fillets raised in the biofloc system and control treatment, fillet color, taste, texture, chew ability, and general acceptability did not exhibit any significant differences among different treatments (p>0.05). Using 75% of the feeding required for tilapia in the biofloc system caused an elevation in body protein compared to the control treatment. In addition, the amount of fat also upraised due to the employment of this system. Using single-celled algae resulted in an increase in the amount of biofloc and an effect on the composition of Nile tilapia fish fillets.

Oak acorn is widely used as human food and animal feed. This fruit contains considerable amounts of tannin. A large amount of tannin causes a disturbance in the digestion process. The aim of this study was to reduce the amount of tannin before consuming oak acorn in the diet. Dry and de-hulled acorns were soaked in tap water (1:5; w/v) for 24, 48 and 72 h (treatments 1, 2 and 3 without water exchange and treatments 4, 5 and 6 with water change every 12 h, respectively) at 50 °C. Then acorns were dried at 60 °C for 24 h, milled and sieved with a 250-micron sieve. The highest loss of total phenolic compounds (93.34%), non-tannin phenolic compounds (95.83%) and condensed tannins (96.92%) and the highest increase in protein digestibility were observed in treatment 6 (p<0.05). Carbohydrate digestibility only in treatment 2 was higher than the control, and the increased soaking time from 48 to 72 h caused a significant decrease in the digestibility of the carbohydrate. Acorn soaking caused a significant elevation in pH in treatment 6. The pH value of digested acorn was not different from the control when water was not changed, however, it was higher than the control when water was changed. In general, treatment 6 is recommended as the best treatment in acorn processing with tap water.

In this study, the comparative effects of arachidonic acid (ARA) enrichment of the concentrated food and live feed (Artemia nauplius) were investigated on growth rate and reproductive indices in zebrafish (Danio rerio). Thirty-day-old juveniles (n = 400, with an average initial weight of 0.125 g) were randomly distributed in six treatments (each in three replicates) in eighteen 10-L aquariums (with a stocking density of 15 juveniles per aquarium). Fish were fed with concentrated diet containing three levels of ARA (0, 1 and 2% in the diet) and live feed (Instar II Artemia nauplii) in three levels of ARA (0, enriched with 1% and 2% of ARA) for 60 days until sexual maturity. The results of Two-Way ANOVA showed that the final body weight, body weight gain rate (%), and female’s reproductive indices were not affected by the combined effects of two factors; food type and ARA levels (p>0.05). Body weight in fish fed with concentrated diet containing 2% ARA was significantly higher than compared with the other treatments (p<0.05). The highest absolute and relative fecundities, and gonadosomatic index were obtained in females fed ARA-free concentrated diet, the enriched- Artemia with 1-2% ARA, and the enriched- Artemia with 1% ARA (p<0.05), respectively. The ARA enrichment in the concentrated diet only accelerated the growth rate of fish until sexual maturity for breeding. However, fish fed the enriched- Artemia with 1% ARA exhibited higher gonadal weight and much higher relative fecundity compared to other groups despite lower final weight (p<0.05). Based on the results and in order to improve the female’s reproductive performance in zebrafish hatcheries, it is suggested that fish fed the enriched Artemia with 1% ARA two months before reproduction.