Fishmeal, plant protein, and fish oil substitution with single-cell ingredients in organic feeds for European sea bass (Dicentrarchus labrax).

Single-cell ingredients (SCI) are considered promising nutrient sources which are produced using environmentally friendly biotechnological processes. The aim of the current study was to evaluate the replacement of fishmeal, plant protein sources, and fish oil with SCI in organic feeds for European sea bass (Dicentrarchus labrax). Bacterial protein, yeast protein, and microalgae were used to replace fishmeal trimmings, soya bean meal, and fish oil from trimmings. Triplicate groups (30 fish per replicate) of European sea bass (14.4 ± 2.4 g) were fed the experimental diets for 71 days. The results showed that the incorporation of SCI at all levels of inclusion significantly enhanced nutrient digestibility. Additionally, growth performance parameters were not affected by SCI inclusion, exhibiting similar or improved values. Moreover, a tendency for improved anterior and posterior gut structure was observed and a significant increase of lysozyme activity at the two highest inclusion levels of SCI was determined. Overall, the results showed that the inclusion of SCI at 15% (bacterial: yeast: algae-9.4: 4.7: 1) is possible without compromising any of the parameters evaluated. According to these findings, a higher substitution of fishmeal trimmings, plant protein sources, and fish oil from trimmings with SCI in organic diets for European sea bass (D. labrax) can be further evaluated in future studies.

Strong effect of long-term Sparicotyle chrysophrii infection on the cellular and innate immune responses of gilthead sea bream, Sparus aurata.

One thousand healthy recipient gilthead sea bream, Sparus aurata, cohabited with 250 donor fish parasitized by Sparicotyle chrysophrii (Van Beneden and Hesse, 1963) (Monogenea: Polyopisthocotylea), a common parasite of the gills of this fish species. Controls consisted of 1000 healthy fish kept in a separate tank. After 10 weeks, fish were weighed and parasite load, hemoglobin concentration and immunological parameters were assessed. Rather than the absence of parasite, hemoglobin concentration was a better marker of the health status of the fish, because S.chrysophrii had detached from the strongly anemic gills of some animals leaving fish with affected immune system but without parasites. The parasite infection seemed to trigger a cellular response of the fish immune system but to inhibit its humoral components. Thus, parasitized fish may control the parasite infection through the action of reactive oxygen species but they may become more sensitive to potential secondary bacterial or parasitical infections. This phenomenon was demonstrated not only through significant differences between recipient and control fish but also through strong correlations between those parameters and parasite load, fish weight and/or hemoglobin concentration.