Dietary intake of beta-1,3/1,6 glucans in juvenile dentex (Dentex dentex), Sparidae: Effects on growth performance, mortalities and non-specific defense mechanisms

Juvenile common dentex (Dentex dentex) Sparidae, were fed moist diets over 2 months. The three test groups (triplicate lay out) received diets supplemented every second week with one of the two tested immunostimulants - MakroGard or VitaStim, or a diet without supplement (control). All fish were weighed at weekly intervals to (a) obtain data on growth and feed conversion and (b) generate repeatedly a defined stress situation to amplify the possible effects of the immunostimulant treatments on growth, mortality and non-specific defense mechanisms. Growth and feed conversion were not significantly influenced by the applied immunostimulants during the entire experimental period. Most likely, as a result of the cumulative handling stress, growth decreased considerably during weeks 5 and 6 of the experiment in all three test groups. Fish in five of the nine test tanks developed a protozoan infection, regardless of the immunostimulant applied. However, mortalities related to this disease were markedly reduced in tanks treated with either MacroGard (10%) or VitaStim (15%) compared to the control tank (30%). Mortalities related either to cannibalism, eye damage or other unidentified events were not significantly different between treated and control tanks. At the end of the experiment, general fish health parameter (Haematocrit, Leucocyte number) and parameter of the non-specific immune response (Oxygen radical activity, Lysozyme activity, Total plasma protein) were determined from blood samples. Blood parameter did not clearly reflect the protective effect of the administered immunostimulants.