M.C. Hidalgo

Comparative study of digestive enzymes in fish with different nutritional habits. Proteolytic and amylase activities

This work provides a comparative study of the proteolytic and amylase activities in six species of fish with different nutritional habits: rainbow trout (Oncorhynchus mykiss), gilthead seabream (Sparus aurata), European eel (Anguilla anguilla), common carp (Cyprinus carpio), goldfish (Carassius auratus), and tench (Tinca tinca). Trout and carp showed the highest digestive proteolytic activity. When proteolytic activity was determined in a wide range of pHs, the highest values in the digestive tract of all species were found at alkaline pHs, except in eel where activity could be detected only at acid pHs. Eel showed the lowest digestive proteolytic potential among all the species studied. With respect to amylase activity, the omnivorous species presented higher activity than did the carnivores. Among the carnivorous species, the lowest activity was found in trout. The ratio of total amylase:total proteolytic activity was higher in omnivorous fish species, the carp having the greatest value, whereas in trout this ratio was lower than one. Digestive enzyme activity declined as the incubation temperature decreased, but this trend varied depending on the fish species and the tissue analyzed.

Influence of the relative proportions of energy yielding nutrients on liver intermediary metabolism of the European eel

Abstract The influence of dietary protein, lipid and carbohydrate proportions on liver glutamate dehydrogenase (GDH), fructose 1,6-bisphosphatase (FBPase), glucose-6-phosphate dehydrogenase (G6PDH) and pyruvate kinase (PK) activities was investigated in the European eel (Anguilla anguilla). The highest weight-gain (%) and feed-efficiency indices were obtained using diets with the highest energy content and, for the same energetic content, those with the greatest carbohydrate level. GDH activity increased in fish fed diets with the highest protein: energy ratio with respect to diets either with lower protein or with higher total energy contents. FBPase showed an increased activity in the liver of fish fed on diets with the lowest carbohydrate content and the highest total lipids concentrations. G6PDH activity correlated positively with dietary carbohydrate concentrations and negatively with dietary lipids levels. The increase of carbohydrates and energy levels in the diet increased liver PK activity. In general terms, the European eel showed a certain capacity to adapt intermediary metabolism to changes in diet composition. Amino acid catabolism increased in response to a higher dietary protein: energy ratio. High carbohydrate levels enhanced glucose utilization to yield energy and lipid formation. Gluconeogenesis increased in response to a lower dietary carbohydrate content. High dietary lipid concentrations reduced gluconeogenesis and lipogenesis from carbohydrates.

Liver and white muscle protein turnover rates in the / European eel Anguilla anguilla: effects of dietary protein quality

Abstract The influence of the quality of dietary protein source on growth and protein synthesis and degradation rates was studied in the liver and white muscle of the European eel. Fish were fed isonitrogenous diets differing in protein source: one (control) contained fish meal, three others incorporating meat meal (MM) or sunflower meal (SFM) as the only protein source, and SFM supplemented with some essential amino acids (EAAs) were also tested. Fish fed diets containing unsupplemented MM or SFM exhibited dietary utilization and growth indices poorer than those fed the control, while EAA supplementation greatly improved the performance of the SFM-diet. Liver showed higher rates of protein synthesis ( k s ) and degradation ( k d ) associated with a higher capacity for protein synthesis per unit of DNA but a lower protein deposition efficiency (PDE), compared to muscle. Low quality dietary protein increased the protein turnover rate, with a higher protein synthesis rate per unit of DNA and RNA but a decrease of PDE. In white muscle, MM and unsupplemented SFM diets decreased k s without changing k d . The MM diet reduced the efficiency of protein synthesis and deposition. EAA supplementation of the SFM diet raised the protein synthesis rate and capacity as well as protein deposition compared to control values.

Feeding of the European eel Anguilla anguilla. I. Influence of dietary carbohydrate level

Abstract 1. 1. Four isoenergetic diets containing different levels of carbohydrate (up to a maximum of 40% in dry matter) and protein (inversely related with carbohydrate, with a minimum of 25% in dry matter) were tested in replicate groups of European eels ( Anguilla anguilla ), with an initial weight of 30–40 g. 2. 2. The diet containing the highest carbohydrate level (therefore, the lowest in protein) provided the best performance and exhibited the most favourable utilization of the dietary protein. 3. 3. It is suggested that dietary carbohydrate could play a more important role as an energy yielding nutrient in the commercial diets for eels compared with the diets of other cultured fish species.

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.

Feeding of the european eel Anguilla anguilla II. Influence of dietary lipid level

Abstract 1. 1. In order to evaluate the possible sparing effect of lipids on protein utilization in a diet for eels, seven experimental diets with different protein/lipid ratios were assayed. 2. 2. The diet producing the best results was that containing 30% protein, 20% lipids, a protein/energy ratio of 16.10 g/MJ gross energy and a total energy content of 19.0 MJ/kg. 3. 3. A general trend of increasing growth rate, an improvement in food conversion and an improvement in the nutritive utilization of dietary protein was recorded as dietary protein/energy decreased, until a value of 16.10 g/MJ was reached. Total dietary energy content was also a determining factor.

Feeding of the European eel Anguilla anguilla. III: Influence of the relative proportions of the energy yielding nutrients

Abstract 1. 1. In order to find the most suitable combination of energy-yielding dietary substrate for eel culture, nine experimental diets provided with different amounts of protein, fat and carbohydrate were assayed. 2. 2. A beneficial effect of reducing dietary protein/energy ratio by increasing the proportion of lipids and/or carbohydrate was observed on growth rate and food conversion. 3. 3. Carbohydrate seems to be more efficient than lipids at producing this sparing action on protein utilization. 4. 4. Perhaps due to their comparatively lower growth rate and to the greater extent of fattening, the pattern of the nutritional requirements of large eels seems to be somewhat different to that established for other carnivorous fish.

On Nutrition and Feeding Studies as the Basis for the Culture of Different Sturgeon Species

Any attempt to save the endangered sturgeon species will depend on the availability of a sufficient stock of the fish in question, as aquaculture is a very suitable tool and has proved feasible for several sturgeon species and, additionally, it could contribute to the development of a new productive activity.

Some functional consequences of partial hepatectomy in rainbow trout (Salmo gairdnerii)

A partial hepatectomy (an average of 36% of hepatic mass removed) was performed in rainbow trout. Thirty days after this partial hepatic removal, the liver had recovered its initial weight. During regeneration the remaining liver was unable to maintain normal blood levels of protein, cholesterol and, partially, lipids which decrease after surgery. The results obtained show that functional and liver weight regeneration proceed at different rates throughout a given time course, weight recovering faster than complete functional restoration.

Description of a facility for studying energy metabolism in fish: application to aquaculture

The main objective of fish culture is to maximise both fish survival and growth rates at the least cost. Studies on nutritional energetics in fish are less developed than in mammals, but fish bioenergetic predictive models could be highly beneficial for aquaculture development. A description is given of a facility built for studying energy metabolism in fish by means of indirect calorimetry. Furthermore, biological assays are performed with the goldfish to verify model adequacy. The installation was designed to determine, together with the analytical techniques required, all the components of an energy budget. In addition, it incorporates the possibility of determining RQ (respiratory quotient) and the knowledge of the proportions in which the different dietary energy-yielding nutrients or reserves are used by the fish under any experimental conditions. The automatization and computerization of the control of the entire system makes it possible to program and perform assays of up to 45 days on duration without interruptions. Other advantages regarding construction and operational characteristics of this calorimetry laboratory are discussed.