Demand feeding and welfare in farmed fish

Following the development of demand-feeding systems, many experiments have been conducted to explore feeding motivation and feed intake in farmed fish. This work aims to review a selection of studies in the field, focusing on three key factors, related to demand feeding and fish welfare. Firstly, we outline how demand feeders should be considered when developing feed management strategies for improving welfare in production conditions. Secondly, via laboratory demand-feeding experiments, we show self-feeding activities depend not only on feeding motivation and social organisation, but also on individual learning capacity and risk-taking behaviour. Thirdly, we report encouraging results demonstrating that when presented with two or more self-feeders containing complementary foods, fish select a diet according to their specific nutritional requirements, suggesting that demand feeders could be used to improve welfare by allowing fish to meet their nutritional needs.     

Proteomic profiling of sea bass muscle by two-dimensional gel electrophoresis and tandem mass spectrometry

In this study, the proteome profile of European sea bass (Dicentrarchus labrax) muscle was analyzed using two-dimensional electrophoresis (2-DE) and tandem mass spectrometry with the aim of providing a more detailed characterization of its specific protein expression profile. A highly populated and well-resolved 2-DE map of the sea bass muscle tissue was generated, and the corresponding protein identity was provided for a total of 49 abundant protein spots. Upon Ingenuity Pathway Analysis, the proteins mapped in the sea bass muscle profile were mostly related to glycolysis and to the muscle myofibril structure, together with other biological activities crucial to fish muscle metabolism and contraction, and therefore to fish locomotor performance. The data presented in this work provide important and novel information on the sea bass muscle tissue-specific protein expression, which can be useful for future studies aimed to improve seafood traceability, food safety/risk management and authentication analysis. This work is also important for understanding the proteome map of the sea bass toward establishing the animal as a potential model for muscular studies.     

Molecular biology and fish welfare: A winning combination

The issue of animal welfare in aquaculture is of growing interest and there is an increasing consumer demand for documentation of safe and ethically defendable food production. In this context, we have looked for molecular markers among those genes whose expression is modified by the different farming conditions. We have compared gene expression of sea bass farmed at different population densities by differential display, and we have obtained six bands differentially expressed whose sequences have been deposited in the public databases; two of them were suppressed by high population density, while four were induced by the treatment. These genes can be used as biomarkers, and together with a panel of stress-related genes of sea bass (D. labrax) that we have already obtained, could allow the rapid diagnosis of the welfare status of a fish using RT-PCR. We are certain that the new molecular techniques will find their place in the everyday management of fish farming. On the other hand, we are also aware that the scarcity of genomic resources for some fish species, in spite of their economical interest, will retard the beneficial effects that modern biotechnology could bring to aquaculture industry. Therefore, an effort should be made to reduce, as far genomic resources are concerned, the gap that separates farmed species from model organisms such as Danio rerio and Fugu rubripes.     

Nano-delivery of trace minerals for marine fish larvae: influence on skeletal ossification,and the expression of genes involved in intestinal transport of minerals,osteoblast differentiation,and oxidative stress response

Currently, the larviculture of many marine fish species with small-sized larvae depends for a short time after hatching, on the supply of high-quality live zooplankton to ensure high survival and growth rates. During the last few decades, the research community has made great efforts to develop artificial diets, which can completely substitute live prey. However, studies aimed at determining optimal levels of minerals in marine larvae compound feeds and the potential of novel delivery vectors for mineral acquisition has only very recently begun. Recently, the agro-food industry has developed several nano-delivery systems, which could be used for animal feed, too. Delivery through nano-encapsulation of minerals and feed additives would protect the bioactive molecules during feed manufacturing and fish feeding and allow an efficient acquisition of active substances into biological system. The idea is that dietary minerals in the form of nanoparticles may enter cells more easily than their larger counterparts enter and thus speed up their assimilation in fish. Accordingly, we evaluated the efficacy of early weaning diets fortified with organic, inorganic, or nanoparticle forms of trace minerals (Se, Zn, and Mn) in gilthead seabream (Sparus aurata) larvae. We tested four experimental diets: a trace mineral-deficient control diet, and three diets supplemented with different forms of trace minerals. At the end of the feeding trial, larvae growth performance and ossification, and the level of expression of six target genes (SLC11A2β, dmt1, BMP2, OC, SOD, GPX), were evaluated. Our data demonstrated that weaning diets supplemented with Mn, Se, and Zn in amino acid-chelated (organic) or nanoparticle form were more effective than diets supplemented with inorganic form of minerals to promote bone mineralization, and prevent skeletal anomalies in seabream larvae. Furthermore, nanometals markedly improved larval stress resistance in comparison to inorganic minerals and upregulated mRNA copy number of OC gene. The expression of this gene was strongly correlated with mineralization degree, thus confirming its potency as a good marker of bone mineralization in gilthead seabream larvae.     

Effects of population density on seabass (Dicentrarchus labrax, L.) gene expression

The issue of animal welfare in aquaculture is growing of interest and there is an increasing consumer demand for documentation of safe and ethically defendable food production. In this context, we have looked for molecular markers among those genes whose expression results modified by the different farming conditions. We have compared gene expression of seabass farmed at different population densities by differential display. We have obtained six bands differentially expressed whose sequences we have deposited in the public databases; two of them resulted suppressed by high population density, while four were induced by the treatment. Population density has, therefore, an effect at gene level by repressing or enhancing the expression of different genes. These genes can be used as biomarkers to rapidly detect, by polymerase chain reaction (PCR), the occurred exposure of the fish to the stressor.

We are certain that the new molecular techniques will find their place in the everyday management of fish farming; on the other hand, we are also aware that the scarcity of the genomic resources for some fish species, in spite of their economical interest, will retard the beneficial effects that modern biotechnology could bring to aquaculture industry. Therefore, an effort should be made to reduce, as far as it concerns genomics resources, the gap that separates farming species from “model organisms”.     

Ascorbate dynamics in embryos and larvae of sea bass and sea bream, originating from broodstocks fed supplements of ascorbic acid

The transfer of L-ascorbic acid (AA) from broodstock to the fertilised eggs and it's dynamics in embryos and fasting larvae, has been studied in sea bass (Dicentrarchus labrax L.) and sea bream (Sparus aurata L.). Two types of diets were fed to the broodstocks: one containing sufficient ascorbate for normal growth and the other with an extra addition of a very high dose (2,000 mg/kg feed) of ethyl-cellulose-coated L-ascorbic acid.The concentration of AA and total ascorbate (L-ascorbic acid plus dehydroascorbic acid) was detected through several embryo and larval development stages, including larvae just before feeding. In sea bass and sea bream, the mean (SD) concentration of total ascorbate in fertilised eggs originating from broodstock fed AA supplemented diet, was 218.5 (17.7) and 122.4 (5.1) g/g wet weight respectively. This was significantly higher (P < 0.01) than the unsupplemented groups, which contained only 155.9 (6.9) and 103.9 (3.5) g/g wet weight respectively. A diet with a vitamin C content adequate for normal growth, may not be sufficient for broodstock when the goal is transfer of TAA to embryos. © Rapid Science Ltd. 1998     

Inflow and outflow water quality control in coastal aquaculture systems: a case study

Coastal water bodies are a particularly heterogeneous resource, typified by high spatial and temporal variability that could influence the aquaculture in coastal zones. However, the development of coastal aquaculture may produce negative impacts on the coastal area by the potential release of nutrients and organic matter that can be a source of pollution in receiving waters. The aim of this paper was to evaluate the performance of constructed wetland in controlling the dynamics of deoxygenating matter (organic matter and ammonia) and eutrophicating matter [organic matter and soluble reactive phosphorus (SRP)] in the waters entering (inflow) and flowing out (outflow) from a coastal aquaculture fish farm. We observed that constructed wetland systems are effective in removing fractions of total suspended solids, COD, total ammonia nitrogen and SRP contained in the inflow water with higher efficiency in the spring period (60.37%, 14.89%, 65.38% and 17.6% respectively) than in the summer period (45.10%, 8.06%, 32.43% and 8.00% respectively). Similar pattern was recorded for the treatment of the outflow waters, showing that the wetland system reduced most of the deoxygenating and eutrophicating matter produced as a consequence of feeding and fish metabolic activity. During the summer season, high algae mortality can reduce the performance of the wetland system in the outflow water control; this lower efficiency could be improved by controlling the biomass of algae by vegetation harvesting.