The influence of high dietary fat levels on protein utilization by the trout, (Salmo gairdnerii)

Relação proteína:carboidrato no desempenho e metabolismo de juvenis de pacamã (Lophiosilurus alexandri)

Objetivou-se neste estudo verificar o melhor nível de inclusão entre proteína e carboidrato no desempenho e algumas respostas metabólicas em juvenis de pacamã (Lophiosilurus alexandri). Testaram-se quatro dietas com as relações proteína/carboidrato (PB:CHO) 1,24; 0,84; 0,51 e 0,33 durante 60 dias. Foram utilizados 240 juvenis de pacamã pesando inicialmente 1,90g, alimentados duas vezes ao dia (8% da biomassa). Avaliou-se o ganho de peso total, taxa de crescimento específico, consumo de ração aparente, conversão alimentar aparente, rendimento de carcaça e gordura visceral. Glicemia, aminoácidos totais livres no plasma e glicogênio hepático também foram avaliados. A relação PB:CHO influenciou (P<0,05) os parâmetros de desempenho e metabolismo, exceto o glicogênio hepático. Maiores concentrações de glicose e aminoácidos totais livres no plasma foram observadas nos peixes que se alimentaram com a dieta contendo a maior relação PB:CHO (1,24). Além disso, observaram-se melhores médias de ganho de peso, taxa de crescimento específico e conversão alimentar aparente. Maiores percentuais de gordura visceral e menor rendimento de carcaça foram observados nos animais submetidos à dieta composta pela menor relação PB:CHO (0,33). Pode-se concluir que a dieta com a relação PB:CHO de 1,24 promoveu melhor desempenho e respostas metabólicas em juvenis de pacamã.

Protein nutrition in fish: protein/energy ratio and alternative protein sources to fish meal

Those interested in the design and manufacture of feeds for intensive fish farming face the basic concern of formulating mixtures for the best yield at the lowest costs. Of the macronutrients in the feed, protein has and continues to receive special consideration because fish present high and specific needs for this constituent. Traditionally, protein has been supplied primarily by fish meals. This paper presents a synthesis of the efforts made and the lines explored to achieve an effective reduction of the amount of fish meal in the feeds for fish, following two strategies: reduction of the protein in the feeds and the use of new raw materials to replace fish meal.

[Significance of extruded feeds for trout nutrition and water protection]

Extruded feeds exhibit an improved starch digestibility and are more firmly bound due to the almost complete gelatinization of the starch. This results in fewer fines and longer water stability than pelleted feeds. Extruded pellets also have the advantage that they can soak up more oil than a conventional pellet. It is therefore possible to increase the maximum oil content to more than 20%. On the other hand extruding feeds is more expensive than steam pelleting. Gelatinized starch is a useful energy source in trout diets helping to reduce feed conversion ratios. Proportions up to 35-40% in the diet are tolerable. Using high dietary levels of both gelatinized starch and oil the non-protein energy of feed may be increased and thus a protein-sparing effect results. High-energy diets enable to reduce excretion of faeces and of nitrogen via gills. In addition a decrease of phosphorus level in feeds and thus of phosphorus excretion by fish is possible. Extruded high-energy diets therefore make a contribution to improve water quality.

Simultaneous effect of initial weight, initial crowding, temperature and O2 concentration on the nutritional use of food by rainbow trout (Oncorhynchus mykiss)

The simultaneous effects of initial weight, initial crowding, temperature and O2 concentration on the following ratios: relative growth rate percent (RGRP), feed efficiency (FE), protein efficiency ratio (PER) and protein productive value (PPV) were studied in the rainbow trout. Multivariant equations were obtained for each of the mentioned indices. The joint effects of these factors were evidenced by means of a multiple correlation analysis. The influence of temperature and, to a lesser extent, of crowding, and O2 concentration on the nutritional use of food by the trout was demonstrated, their fundamental dependence on factors extrinsic to the animal being underlined. The non proportional changes in PER and PPV as temperature rises revealed that an increasing part of the ingested aminoacids were used for synthesis of fat, non for proteins edification.

Aminotransferase activity in the liver and white muscle of Mugil capito fed diets containing different levels of protein and carbohydrate

Four groups of Mugil capito were fed diets with protein and carbohydrate contents changing reciprocally for 121 days. Food consumption changed proportionally to the carbohydrate content of the diet, while final fish growth was similar for all groups of fish. Liver transaminase levels changed significantly with the protein content of the diet. The changes in body transaminase levels were lower in magnitude. The results obtained are compared to those obtained from other fish species and possible reasons for the differences observed are discussed.

Influence of salinity and ratio of lipid to protein in diets on certain enzyme activities in rainbow trout (Salmo gairdneri Richardson)

The connection between metabolic and sea water adaptation of the rainbow trout was investigated. The rainbow trout were kept in fresh water and diluted sea water of 8 and 20 0/00 S at 16 degrees C and fed on three different diets for 51 days. Hyperosmotic salinity (20 0/00) tends to inhibit growth in rainbow trout by reducing the food conversion efficiency. A higher protein concentration in the diet can partly compensate for this effect. The liver IDH, G6PDH and 6PGDH activities of the rainbow trout are influenced only by food quality, whereas the liver G1DH, AspT and A1T activities, like the muscle A1T, are also affected by salinity. The salinity had no significant effect on the activities of the kidney enzymes we investigated (Na/K-ATPase, G1DH, A1T, AspT) or of the muscle AspT in these experiments.

Influence of dietary composition on gluconeogenesis from L-(U-14C)glutamate in rainbow trout (Salmo gairdneri)

The effect of dietary composition (high-protein, high-carbohydrate and high-fat diets) and starvation on in totum gluconeogenesis from L-(U-14C)glutamate was studied in the rainbow trout. High-fat and high-carbohydrate diets produced a significant hyperglycaemia. Lower blood glucose values were obtained in trout fed on a high-protein diet. Liver glycogen levels were significantly lower in trout fed on carbohydrate-free diets (high-protein and high-fat diets) and in starved fish. Gluconeogenesis from L-(U-14C)glutamate was markedly reduced in fish given the high-carbohydrate diet and significantly enhanced in starved fish. Radioactive liver glycogen was higher in starved fish, although the amount of radioactivity incorporated into glycogen was very low.