Influence of early rearing environment on water-borne cortisol and expression of stress-related genes in grass carp (Ctenopharyngodon idella).

Nowadays, lower post-release survivorship of hatchery-reared fish in natural aquatic bodies has attained great attention and research is in progress to determine the reasons for their higher mortality. It is assumed that hatchery rearing environments negatively affect the physiological stress response of the fish. Thus, understanding how rearing environments modulate this is important for the well-being of fish. Here, an attempt has been made to assess the influence of two early rearing environments, i.e., barren (BR), mimic the conventional hatchery rearing environment; without any substrate and enrichment items and structurally enriched (ER), containing multi-colored gravel substrate, cobbles and plants, on the stress regulators i.e., HPI-axis and brain monoaminergic system of fish. Three-day old grass carp (Ctenopharyngodon idella) postlarvae were reared up to the fingerling stage in the aforementioned environments. For the stress assay, fish were subjected to net capture followed by 30 min confinement in a small container at a lower water level. The pre- and post-stress responses were compared by evaluating their water-borne cortisol and the mRNA level of corticotropin releasing hormone (CRH), dopamine D1A receptor (DRD1A) and hydroxytryptamine receptor 2B (HTR2B) in the whole brain through qPCR analysis. Results of two-way ANOVA revealed significantly low (p < .001) post-stress concentration and release rate of water-borne cortisol and pre- and post-stress expression of CRH, DRD1A and HTR2B genes in the ER than BR fish. It is concluded that a structurally complex early rearing environment reduces the stress level in fish.

Evaluation of commercial application of dietary encapsulated probiotic (Geotrichum candidum QAUGC01): Effect on growth and immunological indices of rohu (Labeo rohita, Hamilton 1822) in semi-intensive culture system.

Encapsulated probiotic administration can be a nutritional strategy to improve the growth performance and immune status of fish. Here commercial application of encapsulated G. candidum was evaluated as a feed supplement to fingerlings of L. rohita reared in earthen ponds under semi-intensive culture conditions. Fingerlings with an average body weight of 20 ±â€¯2.34 g were distributed randomly in three groups and experiment was conducted in triplicate. The control group (P0) was fed 35% protein basal diet while the two treated groups, P1 and P2 were fed basal diet supplemented with 109 CFU g-1 un-encapsulated (free) and encapsulated G. candidum, respectively, for eleven weeks. Results indicated significantly (P < 0.05) improved growth rate, intestinal enzyme activities (protease, amylase and cellulase) and hemato-immunological indices (RBCs, Hb, HCT, WBCs, MCHC, respiratory bursts and phagocytic activity, total protein, lysozyme, IgM), upregulation of heat shock protein HSP 70 gene in muscle, intestine and liver tissues and reduction of serum AST and ALT activities, total cholesterol and triglyceride in fish fed G. candidum supplemented diets (P1 and P2 groups) as compared to basal diet (P0 group). However, diet supplemented with encapsulated G. candidum showed the most significant (p < 0.001) positive effect in comparison to un-encapsulated probiotic. In conclusion, a pronounced effect of G. candidum especially in the encapsulated form on the growth, health status and immunity of L. rohita reared in semi intensive culture system, suggesting its application as a feed additive in practical/commercial semi-intensive earthen pond culture system.