Palatability of Water-Soluble Extracts of Protein Sources and Replacement of Fishmeal by a Selected Mixture of Protein Sources for Juvenile Turbot(Scophthalmus maximus)

Poor palatability is a limiting factor for replacing fishmeal with other protein sources in aquaculture. The water-soluble molecules with low molecular weights are the major determinants of the palatability of diets. The present study was conducted to investigate the palatability of water-soluble extracts from single protein source(single extract pellets) and the mixture of these extracts with different proportions(blended extract pellets) in juvenile turbot(Scophthalmus maximus). Then according to the palatability of blended extract pellets, an optimal mixture proportion was selected, and a new protein source made from raw protein materials with the selected proportion was formulated to replace fishmeal. Summarily, the palatability of single extract pellets for turbot was descendent from fishmeal to pet-food grade poultry by-product meal, wheat gluten meal, soybean meal, peanut meal, meat and bone meal, and corn gluten meal. Subsequently, according to the palatability of single extract pellets, 52 kinds of blended extract pellets were designed to test their palatability. The results showed that the pellets presented remarkably different palatability, and the optimal one was diet 52(wheat gluten meal: pet-food grade poultry by-product meal: meat and bone meal: corn gluten meal = 1:6:1:2). The highest ingestion ratio(the number of pellets ingested/the number of pellets fed) was 0.73 ± 0.03, which was observed in Diet 52. Then five isonitrogenous(52% crude protein) and isocaloric(20 k J g^(-1) gross energy) diets were formulated by replacing 0(control), 35%, 50%, 65% and 80% of fishmeal with No.52 blending proportion. After a 10-weeks feeding trial, a consistent feed intake was found among all replacement treatments. Replacement level of fishmeal up to 35% did not significantly influence final body weight, specific growth rate, feed efficiency ratio, and protein efficiency ratio of turbot. Therefore, the water-soluble extracts of protein sources play an important role in improving the palatability of non-fishmeal protein sources in aquafeed.

Feasibility of Partial Replacement of Fishmeal with Proteins from Different Sources in Diets of Korean Rockfish(Sebastes schlegeli)

An 8-week feeding experiment was conducted in an indoor recirculation seawater system to investigate the effects of partial replacement of dietary fishmeal with proteins from five sources on the growth performance and feed utilization of Sebastes schlegeli. Six isonitrogenous and isoenergetic diets were formulated using fishmeal(FM, the control) as sole protein source, or proteins from five sources including poultry by-product meal(PBM), meat and bone meal(MBM), soybean meal(SBM), cottonseed meal(CSM) and canola meal(CNM). Fifteen percent of the crude protein provided by fish meal was replaced, respectively. The results showed that the differences in specific growth rate(SGR) and survival rate(SR) among fish fed PBM, MBM, SBM, CSM and whole FM diets were not significant. However, SGR and SR of fish fed CNM diet was significantly lower than that of other treatments. Feeding rate, feed conversion, nutrient retention showed similar patterns to that of growth. Fish fed CSM and CNM showed significantly lower apparent digestibility coefficient(ADC) of dry matter and gross energy than those fed others while fish fed CNM showed lower ADC of crude protein than those fed others(P<0.05). These results suggested that it was feasible to substitute 15% dietary protein provided by fishmeal with PBM, MBM, SBM and CSM, respectively, but not with CNM as the replacement with CNM reduced fish growth and feed utilization.

Muscle amino acid profiles of eleven species of aquacultured animals and their potential value in feed formulation

The complete quantitative essential amino acid(EAA)requirements of aquacultured animals are largely unknown except for a handful of species.This is problematic because formulation of least-cost diets for target animals demands precise knowledge of EAA requirements.One way of approximating EAA requirements is to use correlations between whole-body and/or muscle EAA profiles using essential to total EAA ratios(A/E ratios).This method requires a reference,quantified EAA requirement,usually lysine(Lys).To systematically evaluate the A/E ratio method,muscle AA profiles were measured in 10 species of teleost and whiteleg shrimp.In fish,Lys represented the dominant muscle EAA measured,ranging between 7.06 and 9.58 g/100 g protein,whereas,in shrimp,arginine(Arg)was quantified as the principal EAA.For non-EAA,glutamate(Glu)and glutamine were consistently the NEAA recorded at highest levels whereas,in shrimp,Glu+Gln was highest followed by aspartate(Asp)plus asparagine(Asn).Except for Arg,which was twice that of fish(P<0.05),whiteleg shrimp expressed similar muscle A/E profiles.Strength of relationship between muscle EAA levels and known requirements were all strongly and positively correlated for non-salmonid species.When using Lys as the reference EAA there were few semblances between measured and estimated EAA requirements.

Recent advances in amino acid sensing and new challenges for protein nutrition in aquaculture

From the conventional knowledge of protein nutrition to the molecular nutrition of amino acids, our understanding of protein/amino acid nutrition is rapidly increasing. Amino acids control cell growth and metabolism through two amino acid-sensingpathways, i.e. target of rapamycin complex 1 (TORC1) and the general control nonderepressible 2 (GCN2) signaling pathway.In the amino acid-abundant status, TORC1 dominates intracellular signaling and increases protein synthesis and cell growth.In contrast, amino acid deprivation actives GCN2 resulting in repression of general protein synthesis but facilitates the aminoacid transport and synthesis process. By integrating and coordinating nutrition and hormone signaling, TORC1 and GCN2control the switch of the catabolism and anabolism phase in most eukaryotes. Now, we appreciate that the availability ofindividual amino acids is sensed by intracellular sensors. These cutting-edge findings expand our knowledge of amino acidnutrition. Although the TORC1 and GCN2 were discovered decades ago, the study of molecular amino acid nutrition inaquaculture animals is still at its infancy. The aquaculture industry is highly dependent on the supply of fishmeal, which isthe major protein source in aquacultural animal diets. Some concerted efforts were conducted to substitute for fishmeal dueto limited supply of it. However, the concomitant issues including the unbalanced amino acid profile of alternative proteinsources limited the utilization of those proteins. Continued study of the molecular nutrition of amino acid in aquacultureanimals may be expected in the immediate future to expand our knowledge on the utilization of alternative protein sources.