Effects of different levels of vitamin C on hatching efficiency and survival of Maharloo Lake Artemia nauplii (Artemia parthenogenetica) at different temperatures

In this study, different levels of vitamin C (L-ascorbyl-2-polyphosphate) on the hatching efficiency and obtained Artemia nauplii survival were examined at different temperatures. In the first experiment, the effect of different amounts of vitamin C (0, 500, 1000 ppm) on hatching percentage of the Maharloo Lake Artemia cyst was examined with 6 replicates. Results of the first experiment showed that different amounts of vitamin C had no significant effect on hatching percentage. In the second experiment, the effect of different temperatures on the percentage of survival of Artemia nauplii was studied. In this experiment, obtained nauplii from first experiment were put in 3 different temperatures (1, 4, 16ºC) with 6 replicates for 48 hours, then percentage of survival of Artemia nauplii accounted. Result of the second experiment showed that interaction of vitamin C and different temperatures had no significant on the survival rate of Artemia nauplii. Different amounts of vitamin C (0, 500, 1000 ppm) had no significant difference on the percentage of survival of the Artemia nauplii, but different temperatures had significant effect on survival rate. Results of these experiments showed that increase of the amount of vitamin C had significant difference on hatching percentage of the Maharloo Artemia cyst, no significant effect on survival rate of Artemia nauplii. Also it is found that survival rate of Artemia nauplii in 16 ºC temperatures was more than 1 and 4 ºC temperatures

Dietary Tryptophan Induces Opposite Health-Related Responses in the Senegalese Sole (Solea senegalensis) Reared at Low or High Stocking Densities With Implications in Disease Resistance

High rearing densities are typical conditions of both inland and onshore intensive aquaculture units. Despite obvious drawbacks, this strategy is nonetheless used to increase production profits. Such conditions inflict stress on fish, reducing their ability to cope with disease, bringing producers to adopt therapeutic strategies. In an attempt to overcome deleterious effects of chronic stress, Senegalese sole, Solea senegalensis, held at low (LD) or high density (HD) were fed tryptophan-supplemented diets with final tryptophan content at two (TRP2) or four times (TRP4) the requirement level, as well as a control and non-supplemented diet (CTRL) for 38 days. Fish were sampled at the end of the feeding trial for evaluation of their immune status, and mortalities were recorded following intra-peritoneal infection with Photobacterium damselae subsp. piscicida. Blood was collected for analysis of the hematological profile and innate immune parameters in plasma. Pituitary and hypothalamus were sampled for the assessment of neuro-endocrine-related gene expression. During the feeding trial, fish fed TRP4 and held at LD conditions presented higher mortalities, whereas fish kept at HD seemed to benefit from this dietary treatment, as disease resistance increased over that of CTRL-fed fish. In accordance, cortisol level tended to be higher in fish fed both supplemented diets at LD compared to fish fed CTRL, but was lower in fish fed TRP4 than in those fed TRP2 under HD condition. Together with lower mRNA levels of proopiomelanocortin observed with both supplementation levels, these results suggest that higher levels of tryptophan might counteract stress-induced cortisol production, thereby rendering fish better prepared to cope with disease. Data regarding sole immune status showed no clear effects of tryptophan on leucocyte numbers, but TRP4-fed fish displayed inhibited alternative complement activity (ACH50) when held at LD, as opposed to their HD counterparts whose ACH50 was higher than that of CTRLfed fish. In conclusion, while dietary tryptophan supplementation might have harmful effects in control fish, it might prove to be a promising strategy to overcome chronic stress-induced disease susceptibility in farmed Senegalese sole

Nitrogenous compounds and oxygen concentration as the key density dependent factors to optimize growth of beluga, Huso huso (Actinopterygii: Acipenseriformes: Acipenseridae), in circular fiberglass tanks

Background. Beluga, Huso huso, known also as the great sturgeon, is a valuable fish in terms of meat and caviar production. It has been implicated that intensive fish culture is a major culprit for deterioration of water quality through metabolic excretion of fish in the aquatic environment. The aims of this study were: to determine the effect of the stocking density on the water quality, to assess the effect of water quality changes on growth of beluga juveniles, and also to determine the optimum density for culture in fiberglass tanks. Materials and methods. Fish were randomly distributed into 15 tanks at 5 different densities including 1 kg · m–2 (3.90 kg m–3), 2 kg · m–2 (7.09 kg · m–3), 4 kg · m–2 (14.54 kg · m–3), 6 kg · m–2 (21.19 kg · m–3), and 8 kg · m–2 (28.64 kg · m–3) with 3 replicates. Specific growth rate (SGR), yield (Y), average daily growth (ADG), absolute weight gain (AWG), and relative weight gain (RWG) were calculated. Throughout the experiment, water quality parameters including ammonia (NH3), nitrite (NO2), nitrate (NO3) dissolved oxygen (DO), and oxygen saturation (OS) were also measured. Results. Stocking density considerably influences the growth of beluga juveniles and water quality during 56 days of rearing. DO, OS, NO2, NO3, and NH3 were significantly different among treatments. pH and temperature showed no significant effect under different stocking densities. NO2 and NO3 increased, while DO decrease as the stocking density of fish increased. At the end of the 56 days of rearing, all the growth parameters (final weight, total length, SGR, Y, ADG, AWG, and RWG) were significantly different among treatments. Survival was 100% in all of the rearing densities. Conclusion. Results of this study showed that the density of fish had a significant effect on water quality and a high density culture accompanied by intensive feeding may result in high concentrations of nitrogen compounds, and low concentrations of dissolved oxygen in the water of culture tanks. Each of the factors (increase nitrogenous compounds and decrease in oxygen) could suppress the growth of Huso huso juveniles