BACKGROUND: Although several types of in vitro digestibility assays have been applied to nutritional evaluation of feeds for aquatic organisms, all of them are based on the use of closed reactors and do not simulate the gastric phase of the digestion. Our objective was to evaluate the suitability of a gastrointestinal model based on the use of a digestion cell provided by a semi-permeable reaction chamber, which allows continuous removal of digestion products as they are produced. We tested the effects of some factors, like the inclusion of a gastric phase, reaction temperature or bile salts on the hydrolysis of feed proteins by fish enzymes.

This study investigates the effect of digestible protein levels in experimental diets for meagre (Argyrosomus regius). A group of 253 fish, 52 g of mean weight, was distributed in 12 tanks, three replicates per treatment. Four isolipidic diets (170 g kg−1 crude lipid) with different digestible protein levels (350 g kg−1, 430 g kg−1, 490 g kg−1 and 530 g kg−1) were formulated using commercial ingredients. The trial lasted 62 days. Meagre fed diets 430, 490 and 530 g kg−1 obtained higher TGC (2.47, 2.57, 2.69 × 10−3, respectively) than fish fed diet 350 g kg−1 (2.14 × 10−3). Group of fish fed diet with 350 g kg−1 DP showed the lowest ammonia excretion level. According to the in vitro digestibility trial diets with 350 and 430 g kg−1 DP released less amino acids in comparison with diet with 49% DP, although in vivo digestibility test did not show significant differences among diets 430, 490 and 530 g kg−1 DP. Using the quadratic regression, optimal digestible protein intake according to the ECR for rearing juvenile meagre was recorded in 0.8 g DP/100 g fish and day.

An in vitro model designed to assess protein bioavailability in diets for growing Octopus was developed. The model required a previous assessment of some functional features of protein digestion in this species like the main producing organs, optimum pH for activity and total production per g tissue. The main producing organs identified were the salivary glands and the hepatopancreas (HP), being optimum pH for protease activity quite different in both organs (mostly alkaline in the posterior salivary glands and acid in the HP). In spite of the high-specific protease activity measured in the salivary glands, a major role of the HP in protein hydrolysis is suggested due to the much bigger size of this viscera. All this information was used as a basis to develop an in vitro two-step hydrolysis process, which simulated protein hydrolysis performed by these two organs using the Octopus enzymes. The assay was used to evaluate differences in amino acid bioavailability from several protein sources (casein, gelatin, fish meal, squid meal and krill meal) that could be used as feed ingredients for this species. As significant differences were detected both in total amount and in rate of release of the amino acids from such proteins, the model is proposed as a complementary tool in the selection and nutritional evaluation of protein ingredients to be used in diets for Octopus.

No abstract

Centropages tenuiremis Thompson I.C. and Scott A., 1903 was described for the first time from the waters of Ceylon (Sri Lanka). However, the current distribution of this invasive species has been recorded from Japanese waters, Korean Peninsula, Taiwan, Andaman Sea, India and also the Arabian Gulf. Of late, C. tenuiremis has been recorded from numerous localities of Southeast Asian waters, often with no attempt at justification of identification. Centropages tenuiremis was initially discovered in mid-March 2020 in a sample taken during a long-term plankton survey along the west coast of Johor (Straits of Malacca) started. This study aimed to identify the invasive C. tenuiremis morphologically to meet the attributes for introduced species which are based on the premise of morphologic accuracy.