Effects of immunostimulants on ranched southern bluefin tuna Thunnus maccoyii: immune response, health and performance

The Effects of β - Glucan on Fish Immunity

Administration of glucans through immersion, dietary inclusion or injection has been found to enhance many types of immune responses, resistance to bacterial and viral infections and to environmental stress in many fish species. Although the efficacy of the glucan varies with types and administration, glucan used as an immunomodulatory and mostly immunostimulatory additive has been found satisfactory in eliciting immunity in commercial aquaculture. Development of more efficient administration methods will facilitate the routine and prophylactic use of glucans as natural immunostimulants of fish. Using a PubMed search, this review has an extensive literature on glucan in fish immunity.

Enrichment of gilthead seabream (Sparus aurata L.) diet with microalgae: effects on the immune system

The present study assessed the effects of three orally administered microalgae (Nannochloropsis gaditana, Tetraselmis chuii and Phaeodactylum tricornutum) on different immune parameters and immune-related gene expression of gilthead seabream (Sparus aurata L.). Fish were fed a control or one of six experimental diets and sampled at 2 and 4 weeks of treatment. At the end of the trial, growth performance and different systemic and local immune activities were measured (natural haemolytic complement activity, IgM levels, phagocytosis and respiratory burst). The expression levels of different immune-associated genes (EF-1α, IgM(H), TCR-β, MHCIα, MHCIIα, CSF-1R and β-defensin) were analysed in head-kidney and gut. Administration of N. gaditana and T. chuii resulted in a significant increase in haemolytic complement activity, phagocytic capacity, as well expression level of β-defensin, as well as MHCIIα and CSF-1R, respectively. The P. tricornutum-supplemented diet provoked immunostimulation, and very little effect on gene expression was observed. These results suggest that dietary microalgae enhance gilthead seabream defence activity, which could be very important in order to consider such microalgae as a possible additive in fish diets.

Correlation of humoral immune response in southern bluefin tuna, T. maccoyii, with infection stage of the blood fluke, Cardicola forsteri

The blood fluke, Cardicola forsteri, is a prevalent infection in ranched southern bluefin tuna. This project aimed to define the timing and intensity of the various developmental stages of C. forsteri within southern bluefin tuna as well as to relate infection to host pathology and immune response. Archival samples from several cohorts of T. maccoyii sampled from 2008 to 2010 were used in this study. The prevalence and intensity of C. forsteri infection was described using heart flushes and histological examination. Humoral immune response, i.e. C. forsteri specific antibody, lysozyme activity, and alternative complement activity, was also described. Based on the validated and detailed C. forsteri infection timeline, relationships between infection events, physiological response, and diagnosis were proposed. Immune response developed concurrently with C. forsteri infection, with the majority of physiological response coinciding with commencing egg production. Further research is needed to confirm the origin of C. forsteri antigen which is responsible for immune response development and how T. maccoyii immune response works against infection. To aide this research, further diagnostic methods for confirmation of infection need to be developed.

Moving cages further offshore: effects on southern bluefin tuna, T. maccoyii, parasites, health and performance

The effects of offshore aquaculture on SBT health (particularly parasitic infections and haematology) and performance were the main aim of this study. Two cohorts of ranched Southern Bluefin tuna (SBT) (Thunnus maccoyii) were monitored throughout the commercial season, one maintained in the traditional near shore tuna farming zone and one maintained further offshore. SBT maintained offshore had reduced mortality, increased condition index at week 6 post transfer, reduced blood fluke and sealice loads, and haematological variables such as haemoglobin or lysozyme equal to or exceeding near shore maintained fish. The offshore cohort had no Cardicola forsteri and a 5% prevalence of Caligus spp., compared to a prevalence of 85% for Cardicola forsteri and 55% prevalence for Caligus spp. near shore at 6 weeks post transfer. This study is the first of its kind to examine the effects of commercial offshore sites on farmed fish parasites, health and performance.