Browsing by Author "Tomkiewicz, Jonna"
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- First assessment of prebiotics, probiotics, and synbiotics affecting survival, growth, and gene expression of european eel (anguilla anguilla) larvaePublication . Politis, Sebastian N.; Benini, Elisa; Miest, Joanna J.; Engrola, Sofia; Sørensen, Sune R.; Syropoulou, Elisavet; Butts, Ian A. E.; Tomkiewicz, JonnaEuropean eel, Anguilla anguilla, larval culture faces a bottleneck during the transition to exogenous feeding. To stimulate gut-priming, in the present study, prebiotics (AgriMOS, mannan-oligosaccharides, and beta-(1,3 and 1,6)-poly-D-glucose), probiotics (Bactocell, Pediococcus acidilactici), and synbiotics (AgriMOS + Bactocell) were administered to European eel larvae during the endogenous prefeeding stage. Eel larvae were reared in 2 L incubators with an initial stocking density of similar to 200 larvae/L. Each treatment (pre-, pro-, synbiotics, and control), represented by 3 replicated incubators, was connected to a separate recirculating aquaculture system. The gut-priming agents were introduced directly into the rearing water. Results revealed increased mortality when larvae were introduced to synbiotics and impaired growth in connection to probiotics and synbiotics. Larvae receiving prebiotics showed similar survival and growth to larvae reared without gut-priming agents. The immune gene expression revealed a lag phase between maternally inherited protection (c3, igm, and il10) and the gradual buildup of the larvae's own immune system (il1 beta, irf7). The lack of treatment-related immune (c3, igm, il10, il1 beta, and irf7) and stress/repair (hsp70, hsp90) responses revealed an immature immuno-readiness. Digestion (try, ctra, ctrb, tgl, and amyl), food intake (cck), and appetite (ghrl)-related genes were expressed at basal levels already on 4 days post-hatch, which combined with phenotypic plasticity of the appetite-regulating ghrelin (ghrl), indicated a prospective adaptive capability towards earlier maturation of the larval digestive capacity. Overall, we contemplate that the application of gut-priming agents in water has merit; however, as no beneficial effect was observed, we conclude that the regimen applied is not recommendable in the present form and needs to be customized for future eel larval culture. As such, water management strategies and rearing options need to be further explored to establish prefeeding and feeding regimens, targeting optimized culture conditions, and the production of healthy eel offspring.
- Transition from endogenous to exogenous feeding in hatchery-cultured European eel larvaePublication . Benini, Elisa; Engrola, Sofia; Politis, Sebastian Nikitas; Sørensen, Sune Riis; Nielsen, Anders; Conceição, Luis E. C.; Santos, André; Tomkiewicz, JonnaThe transition from endogenous to exogenous feeding is critical during fish early life, where appropriate feed availability and timing of initiation of feeding influence survival. For European eel (Anguilla anguilla), establishing first feeding culture is at a pioneering state, where successful production of larvae has recently enabled feeding experiments. In the present study, three diets and potential benefits of early feeding during the transition from yolk-sac stage to feeding larvae were explored, including molecular analyses of genes involved in digestive functions and growth. Three consecutive trials were performed using hatchery produced eel offspring. In Feeding regimes 1 and 3, expression of npy and cck (appetite regulation) was higher, while expression of pomca (food intake) was lower in non-prefed larvae, indicating increased fasting and higher starvation risk. In contrast, Feeding regime 2 led to the highest survival ever registered for European eel larvae i.e. 20% at 20 dph, in spite that prefeeding resulted in reduced survival rate during the endogenous feeding stage. This was associated with initial hsp90 (stress/repair) upregulation in larvae receiving prefeeding, however, with subsequent downregulation during exogenous feeding. Notably, the growth related gh expression was higher in prefed larvae, indicating growth benefits of prefeeding. Likewise, prefeeding resulted in pomca as well as try, tgl, and amyl2a (digestion) upregulation, providing evidence of beneficial maturation of gut functionalities. Essentially, Feeding regime 2 demonstrated a continuous upregulation of growth, appetite and digestion related genes, which in combination with the highest survival suggest that dietary requirements were partially met. Moreover, in Feeding regime 2, gh and tgl were expressed at a higher level in prefeeding larvae than in the control, indicating that prefeeding might be advantageous in spite observed mortality, but further research is needed, including timing of feed application.