Effect of dietary iron overload on Photobacterium damselae ssp. piscicida pathogenicity in sea bass, Dicentrarchus labrax (L.).

摘要

The effect of prolonged dietary iron overload in sea bass and the role of iron in host-parasite interaction were studied. Forty sea bass were divided into two groups and were fed with either standard commercial fish feed (iron content of approximately 200 mg iron/kg) or the same feed supplemented with 2.5% carbonyl iron which was added to the feed mix prior to pellet extrusion. Blood samples were collected and analysed for total iron (TI), unsaturated iron-binding capacity (UIBC), total iron-binding capacity (TIBC) and transferrin saturation (TS) using the ferrozine method. In addition, samples of the liver and spleen were collected and analysed for tissue iron concentration. At day 390 of iron supplementation, the fish were experimentally infected with a virulent strain of Photobacterium damselae spp. piscicida. Mortality was recorded twice daily for 2 weeks. Results showed that the dietary supplementation of carbonyl iron resulted in changes in sea bass haematological iron parameters, as shown by the moderately increased values of total iron concentration, diminished values of UIBC and consequently elevated transferrin saturation. The haematological iron-overload status was maintained throughout the experiment showing that sea bass were apparently able to control dietary iron absorption to a certain extent, but with continuous iron supplementation, the regulation of absorption was disrupted. The primary target for iron storage was the liver, followed by a progressive splenic iron deposition. The dietary levels of iron had a pronounced effect on the cumulative mortality after exposure to Ph. damselae ssp. piscicida. The fish from the supplemented group became more susceptible to the infectious agent. This showed the importance of iron in the interaction between sea bass and Ph. damselae ssp. piscicida.