Experimental infection model with the bivalvulid Enteromyxum leei (Myxidiidae) in the sharpsnout seabream, Diplodus puntazzo (Sparidae), and evaluation of the antiparasitic efficacy of a functional diet.

An infection model for sharpsnout seabream Diplodus puntazzo (Walbaum) challenged with the myxosporean Enteromyxum leei (Diamant, Lom et Dyková, 1994), resembling the natural infection conditions, was used to evaluate the antiparasitic efficacy of a functional diet. Fish of an average weight of 12.5 ± 1.2 g were delivered either a functional (included as feed supplement at 0.3% levels) or a control extruded diet. After four weeks of administration of the experimental diets, fish were challenged with the parasites (cohabitation with infected donors; donor: recipient ratio 1 : 1). The experiment was terminated four weeks after the start of the challenge. At the end of the experiment, growth and feeding (specific growth rate and feed efficiency), as well as immunological parameters (respiratory burst activity, antibacterial activities, hemoglobin concentration, anti-protease activity and ceruloplasmin activity) were measured along with cumulative mortality and total parasitic count in the gut. No significant difference was evident with regard to growth and feeding performance, mortality, gut parasitic load or immunological parameters as the parasitical challenge significantly affected both the performance of the control and functional diet fed fish. However, there was a less prominent impact on antibacterial, anti-protease and ceruloplasmin activity in fish fed with the functional diet. Overall, the present study validated the experimental cohabitation infection model and evaluated the efficacy of a functional ingredient as an antiparasitic agent, showing some potential effects on the fish immune response.

Variations of physiological and innate immunological responses in goldfish (Carassius auratus) subjected to recurrent acute stress.

This study was undertaken to investigate the influence of repeated acute stress on the physiological status and non-specific immune response of goldfish, Carassius auratus. The acute stress was a succession of a 3 min-chasing period followed by a 2 min-air exposure. The goldfish in triplicate tanks were subjected 3 times daily to this stress for one (S3) or three (S9) days. A separate group of unstressed fish was used as control for each sampling time. Blood samples were collected 12, 48 and 120 h after the last stress procedure. Variations of globulin levels, plasma anti-protease and bactericidal activities were not significant in the present study. The haematological parameters and plasma total protein and albumin strongly declined in S9 fish 12 h post-stress compared to control fish. However, plasma cortisol, glucose and lactate levels in both S3 and S9 transiently increased compared to the control fish. Similarly, plasma peroxidase activity transiently increased in both stressed groups 12 h after stress. An increase in plasma lysozyme and complement activities suggested a hormesis-like effect with one-day acute stress improving the immunological response of goldfish while an extension of the stress period to three days impaired physiology and immunity for up to 5 days. This study revealed that recurrent acute stress could immunosuppress goldfish as usually expected of chronic stress.

Effects of in vitro lactoferricin and lactoferrin on the head kidney cells of European sea bass (Dicentrarchus labrax, L.).

Antimicrobial, anti-inflammatory and immunomodulating properties of lactoferrin have been demonstrated in mammals and in fish. However, in vivo, lactoferrin is digested by gastric pepsin treatment into the N-terminal derived peptide named lactoferricin. This has been so far overlooked in fish in vitro studies. The aim of the present study was to assess in vitro the effects of both lactoferricin and lactoferrin on the head kidney cells of European sea bass (Dicentrarchus labrax, L.) in order to determine their potential as dietary additives and to get some insight into their mode of action. In vitro lactoferricin decreased significantly the chemiluminescent response of head kidney cells but did not affect the zymosan-triggered chemiluminescence activity. On the other hand, a high concentration of lactoferrin directly stimulated chemiluminescence but reduced the zymosan-triggered chemiluminescence. The bactericidal activity of head kidney cells was also significantly diminished by pre-incubation with lactoferrin in a dose-dependent manner. Although no significant effect of lactoferricin or lactoferrin was evidenced on head kidney cellular viability, absent or negative effect on the priming of respiratory burst activity suggested that care should be taken when using lactoferrin in the diet of sea bass and high doses should be avoided. Hypotheses about the mechanisms of action of lactoferricin and lactoferrin are presented.