A plant-based diet supplemented with Hermetia illucens alone or in combination with poultry by-product meal: one step closer to sustainable aquafeeds for European seabass.

BACKGROUND: Increasing demand for high-value fish species and pressure on forage fish is challenging aquaculture to ensure sustainable growth by replacing protein sources in aquafeeds with plant and terrestrial animal proteins, without compromising the economic value and quality of the final fish product. In the present study, the effects of a plant protein-based diet (CV), two plant-based diets in which graded amounts of plan protein mixtures were replaced with Hermetia illucens meal alone (VH10) or in combination with poultry by-product meal (PBM) (VH10P30), a fishmeal (FM) diet (CF) and an FM diet supplemented with H. illucens (FH10) on growth performance, gut health and homeostasis of farmed subadult European seabass were tested and compared. RESULTS: Fish fed the VH10 and VH10P30 diets showed the highest specific growth rates and lowest feed conversion ratios among the tested groups. Expectedly, the best preservation of PI morphology was observed in fish fed the CF or FH10 diets, while fish fed the CV diet exhibited significant degenerative changes in the proximal and distal intestines. However, PBM supplementation mitigated these effects and significantly improved all gut morphometric parameters in the VH10P30 group. Partial substitution of the plant mixture with insect meal alone or PBM also induced most BBM genes and activated BBM enzymes, suggesting a beneficial effect on intestinal digestive/absorption functions. Regarding intestinal microbiota, fish fed diets containing H. illucens meal (FH10, VH10, VH10P30) had the highest richness of bacterial communities and abundance of beneficial genera such as Lactobacillus and Bacillus. On the other hand, fish fed CV had the highest microbial diversity but lost a significant component of fish intestinal microbiota, the phylum Bacteroidetes. Finally, skin pigmentation most similar to that of farmed or even wild seabass was also observed in the fish groups fed CF, FH10 or VH10P30. CONCLUSION: Plant-based diets supplemented with PBM and H. illucens pupae meal have great potential as alternative diets for European seabass, without affecting growth performance, gut homeostasis, or overall fitness. This also highlights the importance of animal proteins in diets of European seabass, as the addition of a small amount of these alternative animal protein sources significantly improved all measured parameters.

Population Genetic Structure and Connectivity of the European Lobster Homarus gammarus in the Adriatic and Mediterranean Seas.

Highly selective fishing has the potential to permanently change the characteristics within a population and could drive the decline of genetic diversity. European lobster is an intensively fished crustacean species in the Adriatic Sea which reaches high market value. Since knowledge of population structure and dynamics is important for effective fisheries management, in this study, we used 14 neutral microsatellites loci and partial mitochondrial COI region sequencing to explore population connectivity and genetic structure by comparing samples from the Adriatic Sea and the adjacent basins of the Mediterranean Sea. The obtained results suggest that neutral genetic diversity has not been significantly affected by decrease in population size due to overfishing, habitat degradation and other anthropogenic activities. Global genetic differentiation across all populations was low (F ST = 0.0062). Populations from the Adriatic Sea were panmictic, while genetic differentiation was found among populations from different Mediterranean basins. Observed gene flow for European lobster suggest that populations in the north eastern Adriatic act as a source for surrounding areas, emphasizing the need to protect these populations by establishing interconnected MPAs that will be beneficial for both fisheries and conservation management.

Competitive feeding interactions between native Ostrea edulis and non-native Crassostrea gigas with implications of introducing C. gigas into commercial aquaculture in the eastern Adriatic Sea.

In order to detect the possible regulatory effect of non-native C. gigas on the native O. edulis, under aquaculture conditions, feeding interactions between them were investigated in a highly productive environment of Lim Bay (Adriatic Sea). The present study uses a multi-methodological approach, including stomach content, DNA barcoding and stable isotope analysis to elucidate the feeding ecology of two oyster species. The research confirmed a high overlap throughout the year in the feeding traits among native and non-native oyster species. Competition for food was not the only relationship that exists between the investigated species as the presence of O. edulis larvae in C. gigas stomach content was confirmed by DNA analysis. Findings are not in favour of introducing C. gigas to commercial aquaculture in any new areas in the Adriatic Sea and support the need to improve the existing O. edulis aquaculture and conserve its wild stocks.

Spatial connectivity pattern of expanding gilthead seabream populations and its interactions with aquaculture sites: a combined population genetic and physical modelling approach.

In gilthead seabream the number of domesticated individuals increased annually, and escape events occur regularly in the Adriatic Sea. Still there is a lack of population genetic characteristics and evidence of the extent and geographic scale of interbreeding resulting from fish-farm escapees. We screened 1586 individuals using a panel of 21 neutral microsatellite loci in several consecutive years and here report on the medium-scale detection of hybrid and farmed seabream in the natural environment. Wild adults showed a lack of genetic structure within basin and sampling years and reduced connectivity with wild offspring collection, suggesting their temporal residency within the Adriatic. On the contrary, by linking the results of multiannual genetic analyses with the results of coupled hydrodynamic and individual based models (IBM-Ichthyop), we observed a strong connection of wild seabream associated with tuna-aquaculture sites and offspring from the nursery grounds, indicating that the surroundings of tuna sea-cage farms can function as a spawning grounds. The study results present the genetic baseline of wild and farmed strains from the eastern Adriatic Sea, as a first step toward development of a mitigation strategy for fish escapees aimed at controlling further erosion of genetic integrity.

Ecological role of bluefin tuna (Thunnus thynnus) fish farms for associated wild fish assemblages in the Mediterranean Sea.

The ecological effects of tuna fish farms are largely undocumented. This study confirmed their high capacity to attract surrounding wild fish. The aggregation effect persisted year round, without detectable seasonal differences. Farm impact was restricted to close proximity of the sea cages, and was more prominent over the bottom than in the water column strata. Tuna fish farms proved to be high energy trophic resources, as indicated by the enhanced fitness status of two focal species, bogue and seabream. Under abundant food supply, seabream appear to allocate the majority of energy reserves to gonad development. Farm associated bogue had greater parasite loads, with no detrimental effect on fitness status. Overall, tuna fish farms can be regarded as population sources for aggregated wild fish, and under the no fishing conditions within the leasehold areas, can serve as functional marine protected areas.