M.D. Suárez

Evaluation of lupin seed meal as an alternative protein source in feeding of rainbow trout (Salmo gairdneri)

Abstract The nutritive quality of trout diets including lupin seed meal at 10, 20, 30 and 40% of dietary protein content was evaluated. Influence of heating on nutritional quality was also tested. Food intake, conversion index, digestibility of dietary protein, protein efficiency ratio and protein productive value were the parameters evaluated. The possibility of including crude lupin seed meal in trout diets at levels as high as 30% of dietary protein was demonstrated. Heating did not improve nutritional quality.

Metabolic effects of changes in the dietary protein: carbohydrate ratio in eel (Angilla anguilla) and trout (Oncorhynchus mykiss)

The metabolic consequences of the isoenergetic replacement of dietaryprotein by carbohydrates (CHO) were compared in studies of European eel andrainbow trout. Diets with 45/20, 37/30, 29/40 and 21/50 percentprotein/carbohydrate were assessed during a 12-week experiment. The CHO sourcewas pre-gelatinized corn starch. Fish of initial average weight 45gwere fed to satiation twice daily. Weight-gain and feed-efficiency data weregenerally better in trout than in eel, presumably because trout digestibilitycoefficients for protein and energy were higher than in eel. In both species,regardless of physiological differences in digestion and absorption, feedintakeand nutrient digestibility were lower when dietary CHO was higher, but theinter-species differences decreased with increasing dietary CHO.Pyruvate kinase activity (PK) in trout was not affected by dietary CHO content,while blood-glucose and liver-glycogen levels significantly rose withincreasingdietary CHO. In contrast, blood-glucose levels appeared to be regulated ineels,perhaps by an accelerated glycolysis rate, revealed by changes in PK.Gluconeogenic activity was inhibited in trout fed a diet containing20–30%CHO, while in eels this activity was not inhibited by dietary replacement ofprotein by carbohydrate. Liver glucose 6-phosphate dehydrogenase activity(G6PDH) was inhibited in trout fed increasing dietary CHO, whereas in eelsG6PDHoperated at a high rate regardless of dietary composition. These results mayindicate that eels have a better capacity for metabolising high-CHO/low-proteindiets than do trout.

Effect of feeding method and protein source on Sparus aurata feeding patterns

The influence of dietary protein source (fishmeal, soy-protein concentrate and soy-protein concentrate supplemented with methionine) on voluntary feed intake, daily feeding rhythm and nutritive utilisation of diet was studied in the gilthead sea bream (Sparus aurata) fed by hand or demand feeding. Fish weighing 21 g were maintained indoors under natural conditions of temperature and photoperiod (transparent ceiling) and allowed ad libitum or self-feeding of experimental diets for 26 days, with three replicates per treatment. In the first experiment, the influence of hand or demand feeding on growth rate and feed utilisation of a fishmeal-based control diet was studied. In a second trial, involving different protein sources, fish were maintained under the experimental conditions for 6 days after 20 days training. The general composition of the experimental diets was: 45% protein, 14% lipids and 20% carbohydrates. Results showed that: (1) gilthead sea bream preferentially feed in the afternoon and evening; (2) demand feeding improved both food conversion and protein efficiency; (3) the protein source appeared to induce changes in the timing of feeding; and (4) supplements of methionine advanced the time of feeding and lengthened ingestion phases. D 2003 Elsevier Science B.V. All rights reserved.

Utilization of dietary protein by the eel (Anguilla anguilla): Optimum dietary protein levels

Abstract European eels, with mean initial body weight of 40 g and maintained at 25°C, were fed on diets of different protein content (35, 40, 45, 50 and 55% protein), for 60 days. Two fish-protein sources, white fish meal (WFM) and herring meal (HM), were separately tested at the stated protein levels. WFM was a better protein source than HM, for all the protein levels assayed, as observed by feed conversion, protein efficiency for growth and apparent digestibility. For both protein sources the optimal daily protein intake for maximum growth was about 1.4 g 100 g fish.

Utilization of dietary carbohydrates by fish: a comparative study in eel and trout

To evaluate the ability of the eel to use diets with high carbohydrate content, a comparative study was made by using the rainbow trout, a carnivorous fish, as a reference species. Four isoenergenetic diets (in terms of gross energy) were formulated incorporating different protein/carbohydrate ratios (450/200, 370/300, 290/400 and 210/500 as g/kg dry matter, respectively) and each one was tested in three replicates groups of eels and trout. The data on growth, food conversion and utilization of dietary protein and energy show that the eel has a comparatively greater ability than the rainbow trout for using diets with a high carbohydrate level. Thus it is postulated that higher carbohydrate levels could be used for formulating cheaper diets.

Freezing and Freezing-Thawing Cycles on Textural and Biochemical Changes of Meagre (Argyrosomus regius, L) Fillets During Further Cold Storage

The effects of freezing and freezing-thawing cycles during cold storage have been studied in meagre (Argyrosomus regius) fillets. Fillets were subjected to three conservation protocols: fresh, freezing at –20°C, and repeated freezing-thawing cycles. Fresh fillets were stored (4°C, 15 days), and the same protocol was followed for freezing and freezing-thawing after the freezing period. Freezing and freezing-thawing fillets were softer and presented lower water holding capacity than fresh, mostly attributable to collagen solubilization, and partial myofibrillar protein degradation. Cold storage (4°C) during 15 days caused softening in fresh and frozen fillets attributable to myofibrillar protein hydrolysis. Freezing-thawing cycles increased proteolysis, this leading to unacceptable softening even from early stages of further cold storage, and this was also revealed by SDS-PAGE.

Influence of pre-slaughtering feed restriction on muscle characteristics of farmed sea bass (Dicentrarchus labrax L.) during cold storage

BACKGROUND This paper deals with the consequences of dietary restriction or complete starvation before slaughtering on the biochemical and textural characteristics of sea bass muscle. RESULTS Results showed that only severe feed restriction influenced negatively total body and individual organ weights, and these animals showed lower condition factor as well. Neither moderate feed restriction (up to 50% of the standard ration) kept for 30 days nor total starvation up to 12 days caused significant effects on fish weight and fillet yield. Muscle lipid content was lower in feed-restricted fish, although this parameter was not altered by starvation time. Differences between the two feeding strategies studied were observed in muscle textural and biochemical parameters, and the results point to an influence of the nutritional status on the post-mortem evolution of collagen and myofibrillar proteins, although firmness was not modified. CONCLUSIONS Moderate feed restriction prior to slaughtering could be advisable in sea bass culture, given that no detrimental effects on fish quality or fish performance were noticed, whereas substantial amounts of feed can be saved.

Effects of vacuum and modified atmosphere on textural parameters and structural proteins of cultured meagre (Argyrosomus regius) fillets.

The influence of two preservation strategies (vacuum package and modified atmosphere package) on the post-mortem changes of textural parameters, pH, water holding capacity, sarcoplasmic and myofibrillar proteins, and collagen content of meagre (Argyrosomus regius) fillets was studied. Fillets were stored in a cold room in aerobic (control, C), vacuum (V) and modified atmosphere (MA) package. Samples were withdrawn at six sampling points throughout 15-day storage, and post-mortem changes were assessed. The textural parameters were significantly enhanced in V and MA compared to C. Both V and MA treatments reduced the intensity of a group of myofibrillar protein fractions (140–195 kDa) and increased insoluble collagen compared to C. Consequently, the post-mortem flesh softening in C was attributed to increased proteolysis in both intracellular and extracellular structural proteins. The preservation of the textural and biochemical characteristics of meagre fillets subjected to V and MA treatments makes these two treatments highly recommendable for the commercialization of meagre fillets.

Effect of sublethal concentrations of waterborne copper on lipid peroxidation and enzymatic antioxidant response in Gambusia holbrooki

The aim of the current research was to assess the possible influence of copper sulphate contamination on the antioxidant enzymatic defenses and lipid peroxidation (LPO) in the mosquitofish (Gambusia holbrooki). Quadruplicated lots of this fish were exposed to three increasing sub-lethal concentrations of Cu (0.10; 0.17 and 0.25mgCu/L) and a control without Cu for 20 days. Previous to laboratory acclimation, 8 fish were taken to define the initial population. At the end of the trials, 12 fish/sex/treatment were sampled for the determination of levels of copper in gills, metallothioneins (MTs) content, total lipids, fatty acids profiles and antioxidant enzymatic activity, as well as lipid peroxidation. Most of the antioxidant enzymatic defenses assayed were not activated and lipid peroxidation decreased significantly in fish exposed to any concentration of copper applied. This leads us to presume the existence of a protective mechanism against peroxidation other than the enzymatic antioxidant defense, which could be related to the observed increase of copper content in the gills.