Acclimation of Anabas testudineus (Bloch) to three test temperatures influences thermal tolerance and oxygen consumption

Teleost fish have developed their own specific adaptive mechanism, both behavioral and physiological, to maintain homeostasis in response to unfavorable temperatures. Therefore, this study was aimed at assessing the critical thermal maxima (CT(Max)), critical thermal minima (CT(Min)), and oxygen consumption rate of Anabas testudineus (17.03 +/- 1.2 g) after acclimating to three preset temperatures (25, 30, and 35 degrees C) for 30 days. The CT(Max) and CT(Min) were 40.15, 41.40, 41.88 degrees C and 12.43, 13.06, 13.94 degrees C, respectively, and were significantly different (P < 0.05). The thermal tolerance polygon for the specified temperatures was 278.30 degrees C(2). The oxygen consumption rate (117.03, 125.70, 198.48 mg O(2) kg(-1) h(-1), respectively) increased significantly (P < 0.05) with increasing acclimation temperatures. The overall results indicate that the thermal tolerance and oxygen consumption of A. testudineus are dependent on acclimation.

Poly-beta-hydroxybutyrate (PHB) increases growth performance and intestinal bacterial range-weighted richness in juvenile European sea bass, Dicentrarchus labrax

The bacterial storage polymer poly-beta-hydroxybutyrate (PHB) has the potential to be used as an alternative anti-infective strategy for aquaculture rearing. In this research, the effects of (partially) replacing the feed of European sea bass juveniles with PHB were investigated. During a 6-week trial period, the PHB showed the ability to act as an energy source for the fish. This indicated that PHB was degraded and used during gastrointestinal passage. The gut pH decreased from 7.7 to 7.2 suggesting that the presence of PHB in the gut led to the increased production of (short-chain fatty) acids. The diets supplemented with 2% and 5% PHB (w/w) induced a gain of the initial fish weight with a factor 2.4 and 2.7, respectively, relative to a factor 2.2 in the normal feed treatment. Simultaneously, these treatments showed the highest bacterial range-weighted richness in the fish intestine. Based on molecular analysis, higher dietary PHB levels induced larger changes in the bacterial community composition. From our results, it seems that PHB can have a beneficial effect on fish growth performance and that the intestinal bacterial community structure may be closely related to this phenomenon.

AI-2 quorum-sensing inhibitors affect the starvation response and reduce virulence in several Vibrio species, most likely by interfering with LuxPQ

The increase of disease outbreaks caused by Vibrio species in aquatic organisms as well as in humans, together with the emergence of antibiotic resistance in Vibrio species, has led to a growing interest in alternative disease control measures. Quorum sensing (QS) is a mechanism for regulating microbial gene expression in a cell density-dependent way. While there is good evidence for the involvement of auto-inducer 2 (AI-2)-based interspecies QS in the control of virulence in multiple Vibrio species, only few inhibitors of this system are known. From the screening of a small panel of nucleoside analogues for their ability to disturb AI-2-based QS, an adenosine derivative with a p-methoxyphenylpropionamide moiety at C-3′ emerged as a promising hit. Its mechanism of inhibition was elucidated by measuring the effect on bioluminescence in a series of Vibrio harveyi AI-2 QS mutants. Our results indicate that this compound, as well as a truncated analogue lacking the adenine base, block AI-2-based QS without interfering with bacterial growth. The active compounds affected neither the bioluminescence system as such nor the production of AI-2, but most likely interfered with the signal transduction pathway at the level of LuxPQ in V. harveyi. The most active nucleoside analogue (designated LMC-21) was found to reduce the Vibrio species starvation response, to affect biofilm formation in Vibrio anguillarum, Vibrio vulnificus and Vibrio cholerae, to reduce pigment and protease production in V. anguillarum, and to protect gnotobiotic Artemia from V. harveyi-induced mortality.

Modulation of key metabolic enzyme of Labeo rohita (Hamilton) juvenile: effect of dietary starch type, protein level and exogenous alpha-amylase in the diet

A 60-day feeding trial was conducted to delineate the effect of both gelatinized (G) and non-gelatinized (NG) corn with or without supplementation of exogenous alpha-amylase, either at optimum (35%) or sub-optimum (27%) protein levels, on blood glucose, and the key metabolic enzymes of glycolysis (hexokinase, HK), gluconeogenesis (glucose-6 phosphatase, G6Pase and fructose-1,6 bisphosphatase, FBPase), lipogenesis (glucose-6 phosphate dehydrogenase, G6PD) and amino acid metabolism (alanine amino transferase, ALT and aspartate amino transferase, AST) in Labeo rohita. Three hundred and sixty juveniles (average weight 10 +/- 0.15 g) were randomly distributed into 12 treatment groups with each of two replicates. Twelve semi-purified diets containing either 35 or 27% crude protein were prepared by including G or NG corn as carbohydrate source with different levels of microbial alpha-amylase (0, 50, 100 and 150 mg kg(-1)). The G corn fed groups showed significantly higher (P < 0.05) blood glucose and G6PD activity, whereas G6Pase, FBPase, ALT and AST activity in liver was higher in the NG corn fed group. Dietary corn type, alpha-amylase level in diet or their interaction had no significant effect (P > 0.05) on liver HK activity, but the optimum crude protein (35%) fed group showed higher HK activity than their low protein counterparts. The sub-optimum crude protein (27%) fed group showed significantly higher (P < 0.05) G6PD activity than the optimum protein fed group, whereas the reverse trend was observed for HK, G6Pase, FBPase, ALT and AST activity. Addition of 50 mg alpha-amylase kg(-1) feed showed increased blood glucose and G6PD activity of the NG corn fed group, whereas the reverse trend was found for G6Pase, FBPase, ALT and AST activity in liver, which was similar to that of the G or NG corn supplemented with 100/150 mg alpha-amylase kg(-1) feed. Data on enzyme activities suggest that NG corn in the diet significantly induced more gluconeogenic and amino acid metabolic enzyme activity, whereas G corn induced increased lipogenic enzyme activity. Increased amino acid catabolic enzyme (ALT and AST) activity was observed either at optimum protein (35%) irrespective of corn type or NG corn without supplementation of alpha-amylase irrespective of protein level in the diet.

Dietary high protein and vitamin C mitigates endosulfan toxicity in the spotted murrel, Channa punctatus (Bloch, 1793)

The amelioration effect of dietary high protein and vitamin C against stress was evaluated in spotted murrel, Channa punctatus, exposed to endosulfan. Two hundred and forty fish (average weight: 27.01 g/fish), distributed equally into 4 different groups (control, T(1), T(2), and T(3)), each with 6 replicates were fed with control (40% crude protein, CP and 0.1% vitamin C), T(1) (40% CP and 0.1% vitamin C), T(2) (50% CP and 0.1% vitamin C), and T(3) (50% CP and 0.2% vitamin C) diets for 90 days. Groups fed T(1), T(2), and T(3) diets were exposed to sublethal endosulfan concentration, whereas the control was maintained without endosulfan exposure. Results indicated significant reduction in the growth performance, survival, and activities of lactate dehydrogenase (liver and muscle), malate dehydrogenase (liver and muscle), enzymes of protein metabolism (aspartate amino transferase in liver and alanine amino transferase in liver and muscle), acetyl choline esterase (brain), alkaline phosphatase activity (liver), and ATPase (gill) enzymes of group fed control diet and exposed to endosulfan. However, endosulfan exposed fish fed high CP and vitamin C diet exhibited significant (P<0.05) improvement in their growth performance and metabolic enzyme activities. Further, high CP and vitamin C diet reduced endosulfan accumulation in the muscle. Overall results indicate that vitamin C (0.2%) supplementation in high CP (50%) diet improves growth, metabolism, and reduce endosulfan bioaccumulation in C. punctatus.

Biochemical and stress responses of rohu Labeo rohita and mrigal Cirrhinus mrigala in relation to acclimation temperatures

The biochemical and stress responses of two Indian major carps, rohu Labeo rohita and mrigal Cirrhinus mrigala were studied after acclimating them to four preset temperatures (26, 31, 33 and 36 degrees C) for 30 days. The blood glucose and liver glycogen levels showed an inverse trend in both the species and were significantly different in L. rohita at higher temperatures. The decrease in the liver glycogen level of C. mrigala, however, was not significant. Plasma cortisol levels increased significantly whereas the ascorbic acid content in the brain and kidney of both the species decreased significantly with increasing temperatures. Total lipid content in the liver of both the species decreased significantly with increasing acclimation temperatures. The phospholipid concentration decreased in L. rohita with increasing acclimation temperatures, and in C. mrigala the values decreased up to 33 degrees C and increased at 36 degrees C. In C. mrigala, the cholesterol level decreased up to 33 degrees C and then increased at 36 degrees C, but the absolute value was lower in comparison to L. rohita. The cholesterol levels, however, were not significantly different in L. rohita. Triglycerides and free fatty acids concentrations decreased significantly with increasing acclimation temperatures in both the species. The present study indicates species-specific metabolic responses of L. rohita and C. mrigala to thermal acclimation.

Digestive enzymes and metabolic profile of Labeo rohita fingerlings fed diets with different crude protein levels

Labeo rohita, commonly called rohu is one of the most important fish species for aquaculture in India. Digestive enzyme response and metabolic profile of fingerling L. rohita to different dietary crude protein (CP) levels (viz. 25, 30, 35 and 40%) were studied in an attempt to optimize a practical diet formulation for this species. After 45 days of feeding, activity of digestive enzymes and metabolite concentrations were assayed. Amylase, lipase and alkaline phosphatase (ALP) activities were not influenced by the dietary protein, but proteolytic and acid phosphatase (ACP) activities varied (P<0.05) between the treatments. Proteolytic activity showed a second order polynomial relationship with dietary crude protein (CP) as Y = 0.0734X(2) + 4.937X - 68.37, r(2)=0.97. A positive correlation was observed between dietary CP and amylase (r(2)=0.78). All the metabolites except muscle glucose showed significant change corresponding to the dietary protein levels. Glucose and glycogen levels corresponded to the dietary carbohydrate levels. Muscle and plasma pyruvic acid increased as the crude protein in the diet increased, whereas liver pyruvic acid showed the opposite trend. Muscle protein content was not affected by dietary CP. Protein fractions in plasma (total protein, albumin and globulin) showed maximum values in 30% CP fed group. It is concluded that proteolytic activity and ACP are the major digestive enzymes responsive to dietary CP in L. rohita fingerlings. Considering the cost effectiveness of the diet, and based on liver and plasma free amino acid levels and plasma protein fractions, 30% crude protein is recommended as the optimal dietary protein for L. rohita fingerlings.

The impact of housing structures on filarial infection

A study was undertaken to correlate the impact of housing and patterns of house construction on the vector density and transmission of filaria among the inhabitants of these houses. Three different types of houses in ecologically similar hamlets of Hariharpur village in Varanasi were selected for determining the density of Culex quinquefasciatus, the vector of Wuchereria bancrofti and its infectivity. The maximum per man hour density of the vector was recorded during March (31.66, 40.33 and 41.33) while minimum was recorded during June (1.3, 2.6 and 0.33) in all the three types of houses. Infection rate in the vectors collected from poorly constructed houses was observed during April, May, October and January of the following year, whereas in moderately constructed houses, infection was observed only in September and in the well constructed houses dissection results did not reveal any infection during the months of the study. Infectivity rate was observed to be 10.0% in moderately constructed houses (group B) during the month of September and 14.2% in poorly constructed houses (group C) during the month of October. Parasitological observations of the population showed a 12.2% microfilaria (mf) rate and 6.7% disease rate among the residents of poorly constructed houses, 5.8% mf rate and 2.9% disease rate among residents of moderately constructed houses. Among residents of well built houses (Group A), none were found to be positive with mf, but disease rate was observed to be 2.7%. Throughout the year the relative humidity was observed to be higher in the poorly constructed houses and ambient temperatures were found to be lower during the summer but higher during the winter than to those of the better constructed houses. The study made evident that the construction of houses plays an important role in the vector's resting preference, leading to a higher density in poorly constructed houses, thereby increasing the possibility of infection within them, and thus maintaining a higher potential for filarial transmission among its inhabitants.