Butyrate is a short-chain fatty acid extensively used in animal nutrition since it promotes increases in body weight and other multiple beneficial effects on the intestinal tract. Although such effects have been demonstrated in several species, very few studies have assessed them in fish. On the other hand, little is known about the metabolic processes underlying these effects. In the present work, growth parameters and changes in more than 80 intestinal metabolites (nucleotides, amino acids and derivatives, glycolytic intermediates, redox coenzymes and lipid metabolism coenzymes) have been quantified in juvenile sea bream fed a butyrate-supplemented diet. Results showed a significant increase in the weight of fish receiving butyrate, while metabolomics provided some clues on the suggested effects of this feed additive. It seems that butyrate increased the availability of several essential amino acids and nucleotide derivatives. Also, the energy provision for enteric cells might have been enhanced by a decrease in glucose and amino acid oxidation related to the use of butyrate as fuel. Additionally, butyrate might have increased transmethylation activity. This work represents an advance in the knowledge of the metabolic consequences of using butyrate as an additive in fish diets.

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The effects of feeding three natural frozen diets, grass shrimp (Palaemonetes sp.), crayfish (Procambarus clarkii) and fish (Sardina pilchardus) and two semi-humid artificial diets (based on fish or shrimp powder) to the cuttlefish, Sepia officinalis, were analysed. Growth rate and feeding rate [FR; % body weight (BW) day )1 ] and food conversions (FC, %) were determined. Cuttlefish fed shrimp grew larger (3.8% BW day )1 ) and had the highest FC, followed by those fed crayfish, and sardine. The highest FR was obtained for cuttlefish fed crayfish (10.5% BW day )1 ). Although both artificial diets were accepted, none produced growth. Digestive gland-to-body weight ratio (DG/ BW ratio) was calculated for animals fed each diet. A positive correlation (r = 0.94) between cuttlefish ingestion FR and DG weight was obtained. Mortality occurred mainly during the last week, and some cannibalism occurred among cuttlefish fed artificial diets. Finally, lipid composition of diets, DG and mantle of each group were analysed. Sardine diet was characterized by high levels of triacylglycerol (TG), whereas the main difference between shrimp and crayfish was the higher n-3/n-6 ratio found in shrimp. Changes in the lipid composition of DG were related to diet, but did not correlate with growth data. A strong loss of TG in the DG of artificial diets groups was notable. No differences in mantle lipid composition among the natural diets were found, but artificial diet groups showed higher contents of neutral lipids in their mantle respect to natural diets. According to results obtained, crayfish (P. clarkii) could be used as an alternative prey for rearing S. officinalis compared with shrimp. Artificial diets showed the worst effects in growth and mortality as well as the stronger influence on DG and mantle lipid composition of cuttlefish. KEY WORDS

The diet of frozen grass shrimp (P. varians) was compared to similar grass shrimp that had suffered either boiling, drying at 60°C, or freeze-drying by lyophilization at -40°C. In experiment 1, cuttlefish fed the frozen shrimp were significantly larger (P \ 0.05) at the end of 10 days and at the end of the experiment, compared with those fed the boiled or dried shrimp. Growth rates were also higher for cuttlefish fed the frozen shrimp, compared with the remaining two. Growth rates were also higher for cuttlefish fed the frozen shrimp, compared with the remaining two. In experiment 2, there were no differences in weight (P [ 0.05) between cuttlefish fed the frozen or the freeze-dried shrimp, whereas cuttlefish fed the dried shrimp were smaller at the end of the experiment. Growth rates of cuttlefish fed the dried shrimp were lower, compared with those for cuttlefish fed the frozen and freeze-dried shrimp, with no significant differences (P [ 0.05) between them. Cuttlefish fed freeze-dried and frozen shrimp showed a higher trypsin activity compared to animals fed boiled and dry (60°C) shrimp. A higher proportion of absorbed energy was channelled into biomass production in animals fed frozen and freezedried shrimp (56% and 43%, respectively) than for animals fed oven-dried (60°C) or boiled shrimp. The heat treatment suffered by the shrimp, either dry or wet, negatively affected diet quality, probably due to denaturation, and loss (by boiling) of proteins and amino acids. Additionally, the heating processes may have oxidized the lipids to a large extent, contributing to the loss of the polar lipids (polyunsaturated fatty acids), which are essential for cephalopods as for other organisms. Freeze-drying by lyophilization (negative temperatures) did not affect the nutritional quality of the shrimp.

Monge-Ortiz, R.; Martínez-Llorens, S.; Marquez, L.; Moyano-Lopez, FJ.; Jover Cerda, M.; Tomas-Vidal, A. (2016). Potential use of high levels of vegetal proteins in diets for marketsized gilthead sea bream (Sparus aurata). Archives of Animal Nutrition. 70 (2)

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The variation in base composition at the three codon sites in relation to gene expressivity, the latter estimated by the Codon Adaptation Index, has been studied in a sample of 1371 Escherichia coli genes. Correlation and regression analyses show that increasing expression levels are accompanied by higher frequencies of base G at first, of base A at second and of base C at third codon positions. However, correlation between expressivity and base compositional biases at each codon site was only significant and positive at first codon position. The preference for G-starting codons as gene expression level increases is discussed in terms of translational optimization.