This study investigated the effects of tuna hydrolysate (TH) inclusion in fishmeal (FM) based diets on the growth performance, innate immune response, intestinal health and resistance to Streptococcus iniae infection in juvenile barramundi, Lates calcarifer. Five isonitrogenous and isoenergetic experimental diets were prepared with TH, replacing FM at levels of 0% (control) 5%, 10%, 15% and 20%, and fed fish to apparent satiation three times daily for 8 weeks. The results showed that fish fed diets containing 5% and 10% TH had significantly higher final body weight and specific growth rate than the control. A significant reduction in blood glucose was found in fish fed 10%, 15% and 20% TH compared to those in the control whereas none of the other measured blood and serum indices were influenced by TH inclusion. Histological observation revealed a significant enhancement in goblet cell numbers in distal intestine of fish fed 5 to 10% TH in the diet. Moreover, fish fed 10% TH exhibited the highest resistance against Streptococcus iniae infection during a bacterial challenge trial. These findings therefore demonstrate that the replacement of 5 to 10% FM with TH improves growth, immune response, intestinal health and disease resistance in juvenile barramundi.

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Bacterial pathogens causing diseases in fishes have broad host ranges, and may cause high mortality or ongoing chronic infections. Pathogen treatments using antibiotics are becoming limited due to increasing concerns for the development of resistance and environmental dissemination of bacteria harboring resistance genes.This study aimed to determine whether nano-emulsions of selected plant-derived essential oils (Origanum vulgare, Eucalyptus globulus, Melaleuca alternifolia and Lavendula angustifolia) were bacteriostatic or bactericidal to Aeromonas hydrophila, Streptococcus iniae and Photobacteriumdamselae subspecies damselae. All treatments showed antibacterial activity, and in almost all cases the activity of the nano-emulsions was superior to their essential oil counterparts. Origanum vulgare (oregano) nano-emulsion had the most effective antibacterial activity, with a minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 3.12 µg/ml against all three species; substantially better than tetracycline. The present study highlights the potential of new formulations of essential oils to enhance bacterial disease control in cultured fish.

The aim of this study was to determine the level of anesthesia attained in Carassius auratus using a propofol bath administration and using values of haematological profile of blood and examinations, to assess the effects of the fish exposure to that anaesthetic. Acute toxicity values of propofol for gold fish were found 96 h LC50 6.353 mg/L, 96 h LC1 2.966 mg/L and 96 h LC99 13.609 mg/L. Time to induce anesthesia in propofol experiment was significantly higher than Clove oil (p < 0.05), but there was no significant difference in recovery time between the experiments. No significant decrease was found in Total RBC, WBC, HCT, MCH, MCV and leukogram indices (p > 0.05). MCHC (%) level of propofol experiment (13.93 ± 1.36) showed significant (p < 0.05) decrease than Clove oil anesthesia (94.95 ± 24.50) and control (62.46 ± 21.90). Hb(g/dl) content (5.20 ± 0.73) showed decrease in propofol exposure compared with control (15.41 ± 4.76) and clove oil experiment (25.39 ± 5.73) (p < 0.05).

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