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Rainbow trout (100 g initial weight) were subjected to the combined effect of two culture densities (15 and 40 kg/m 3 ; D15 and D40, respectively) and two levels of lipids in the diet (14 and 33%; L14 and L33, respectively) during a 75-day experimental period. The results showed worse values for the biometric parameters in trout cultured at higher densities; however, higher lipid content in the diet (L33) offset this negative effect of high densities (D40). Muscle fatty acid composition was affected mainly by the dietary-lipid component, and thus, trout fed with the lower lipid content (L14) showed increased saturated (SFA), monounsaturated (MUFA), and polyunsaturated fatty acid (PUFA) n -3 and reduced PUFA n -6, which could be attributed to the differences in dietary-lipid composition, and a selective preservation of n -3 fatty acids with structural purposes. Feeding a high-lipid diet reduced the firmness and water-holding capacity of fish muscle. Higher culture densities caused darker skin colour, lower muscle pH and water holding capacity values and higher values of maximum rigor strength. [ABSTRACT FROM AUTHOR]

This study describes the stomach development in the sturgeon Acipenser naccarii, focusing on its histoenzymatic and ultrastructural characteristics from hatching until the end of the juvenile phase, 1 month later. The study aims to assist the aquaculturist in identifying the best timing for the start of feeding and to select the appropriate food for each stage of A. naccarii development. At hatching, the anterior portion of the digestive system consists of a yolk sac with a large central yolk mass. The yolk mass is enclosed by differentiating endodermal epithelium. The most significant ultrastructural characteristics of the epithelium are the numerous supranuclear vacuoles containing protein and lipid yolk granules, dilated intercellular spaces, and filiform cytoplasmic projections related to the uptake of reserve material on the apical surface. Newly hatched eleuthero-embryos show optimal enzymatic activities at a pH of 1.5 and 3, which is probably related to the presence of hatching glands and the digestion of yolk components. During the free-embryo phase, the yolk sac epithelium undergoes a series of histological, ultrastructural, and functional modifications to form a cecal stomach with anatomical characteristics similar to those of juvenile specimens. Gastric glands emerge between 6 and 7 days post-hatching (PH), although the absence of secretion granules in their oxyntic-peptic cells indicates that the stomach is not yet functional. During the following days (the exotrophic period), development of the tubular-vesicular network is observed, and secreting granules occur in the cytoplasm of oxyntic-peptic cells until around day 35 after fertilization (day 27 PH), when acid protease enzymatic activity is again detected. These histological and enzymatic changes and the greater number and size of oxyntic-peptic cell secretion granules appear to be related to the gastric compartment ontogeny reaching functionality at this developmental stage. [ABSTRACT FROM AUTHOR]

This work analyses the changes in the redox balance in two fish species: Adriatic sturgeon ( Acipenser naccarii) and rainbow trout ( Oncorhynchus mykiss) during starvation and refeeding period. The starvation period raised the lipid peroxidation (thiobarbituric-acid-reacting substances) levels in liver and blood, while a decline occurred in the antioxidant enzymatic activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GR) in both fish species. In liver, after the refeeding period, SOD activity recovered in both species, whereas CAT activity recovered only in trout. Furthermore, in both tissues of the two species, the lipid peroxidation levels remained high after 2 months of refeeding. In white muscle and heart, the lipid peroxidation levels indicate that these tissues did not undergo oxidative stress during the 72-day period. During starvation, in the muscle of both fish the fall in the lipid peroxidation level coincided with a rise in CAT, GPX and GR. The refeeding period in this tissue raised the lipid peroxidation level, and the enzymatic activities reached the values of the first point of starvation. In heart, no oxidative damage was detected during starvation in either species. The CAT and SOD activities increased during the starvation period only in trout. [ABSTRACT FROM AUTHOR]

Modifications in the chloride (mitochondria-rich) and pavement cells of the gill epithelia of the Adriatic sturgeon Acipenser naccarii after their transfer under hypertonic environmental conditions (salinity 35) were examined by light and electron microscopy. In contrast to freshwater specimens, seawater-acclimated fish showed a marked increase in the number and size of chloride cells. Ultrastructural modifications included: presence of a slightly invaginated apical crypt, a darker cytoplasm, a more compact tubular system, a major increase in cisternae from Golgi apparatus stacks and flattened-out sacs with dilated ends that produced an increase in lateral and basal cell surfaces. All these changes indicated enhanced cellular activity. Pavement cells, which largely covered the chloride cells on the gill filament and lamella, exhibited a complex system of microridges on their apical surface. Typical features included numerous desmosomes that characterized the intercellular junction, and the presence in the apical cytoplasm of bundles of filaments and of electro-dense vesicles in freshwater fish or clear vesicles in seawater-acclimated animals. [ABSTRACT FROM AUTHOR]

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One approach into the lipid requirements and the quality evaluation of the sturgeon Acipenser naccarii is the study of the fatty acid composition of lipids in several tissues. Four different ages of this new target species for freshwater culture were sampled from a fish farm. Oleic and palmitic acids were the most abundant fatty acids in all age groups and tissues sampled. High quantities of 16:1n7, 20:1n9, 22:1n9, 20:5n3 and 22:6n3 were also detected. The overall pattern closely resembles that of other freshwater fish species. No important differences were found in muscle age. The high lipid level and the relatively high proportion of HUFAn3 fatty acids renders this species as a highly desirable food for human consumption. [ABSTRACT FROM AUTHOR]

This experiment was conducted to test two different protein sources as alternatives to the commonly used fish meal (FM) in the diet of the European eel (Anguilla anguilla). Six experimental diets were tested in three replicated lots of European eels. All diets contained the same protein and energy content (ca, 300 g crude protein per kg dry matter and 18·5 MJ/kg, respectively) but differed in the nature of the protein source: FM was the only protein source in the control diet and was fully or partially (0–5: 0–5) replaced by meat meal (MM) or sunflower meal (SFM) in four other diets; a sixth diet included SFM as the only protein source but was supplemented with several essential amino acids. Food intake, fish growth and several indices of diet and protein utilization were measured. MM clearly was the poorest protein source while SFM could replace, at least 0·5 of the FM with no significant reduction in performance. In addition, the European eel was able to utilize the supplement of essential amino acids. The full-SFM diet was improved significantly when supplemented and results were not statistically different from the control FM-based diet. Overall, a good correlation was found between the results of each diet and the respective essential amino acid index, calculated using as reference the essential amino acid requirements previously defined for another eel species, Anguilla japonica. This index could be used as a reliable measure for an a priori evaluation of alternative protein sources to be included in commercial foods for eels. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

Rainbow trout (100 g initial weight) were subjected to the combined effect of two culture densities (15 and 40 kg m −3 , D15 and D40, respectively) and two dietary energy levels (22 and 27 MJ kg −1 E22 and E27, respectively) during a 75-days experimental period. At the end of the experiment, the growth rate as well as the metabolic and oxidative status of liver and muscle of fish were studied. The results showed that combination of culture density and dietaryenergy level negatively affected growth, cholesterol and LDL plasma levels and oxidative stress in muscle. Higher culture density negatively affected the values of total protein, triglycerides, and HDL in plasma, values of hepatic and muscular metabolic activities pyruvate kinase (PK), citrate synthase (CS), and hydroxiacil-CoA dehydrogenase (HOAD); glutamate pyruvate transaminase (GPT) and glutamate oxaloacetate transaminase (GOT) activities in plasma, liver, and muscle; glucose 6P dehydrogenase (G6PDH) activity in muscle; and oxidative stress in liver. High energy intake, adversely affected the hepatic activity of G6PDH, HOAD, GPT and oxidative stress in muscle. Consequently our results indicate that a combination of high culture density and a high level of dietary energy (27 MJ kg −1 in diet) exert a negative impact on the physiology and consequently on the welfare of the farmed fish. [ABSTRACT FROM AUTHOR]

Highlights: [•] Influence of feeding frequency on meagre growth and metabolic parameters was assessed. [•] A feeding regime based on weekly one-day food deprivation appeared to be favourable. [•] Two feed deprivation days per week leads to a reduction in the hepatic metabolic rate. [•] Meagres fed 6 days a week showed lower lypogenic and lipid-storing activities. [•] Fish fed 5 a week showed higher muscle activity due to a higher activity for achieving food. [Copyright &y& Elsevier]

Abstract: Drift macroalgae detached from rocky substrate frequently strands on the shore line, driving a number of ecological processes, such as degradation, consumption, habitat supply and biogeochemical processing. The algal subsidies received by beaches of Foster Bay, in Deception Island, were evaluated in terms of the spatio-temporal dynamics of wrack deposits. Predominance in the strands of a single red blade species, Palmaria decipiens, points toward an equivalent abundance in the subtidal macroalgal beds, accompanied by Desmarestia menziesii and Desmarestia antarctica, among others. Biomass measurements and wrack grooming along the intertidal range over time indicate that an instantaneous stock of 39.9MT of algal debris strands on the shore line of Foster Bay, with more than 50% of these materials being renewed at each tidal cycle. Estimates of macrophyte production fluxing to the bay ecosystems suggest that only a small fraction (2.8%) of the detached material within the bay accumulates as wrack along the intertidal zone. Variability in the amount of algae along the shore is significantly affected by wind direction or coastal orientation, with larger strandings when sea–land winds prevail. The degradative process of algal wrack was analyzed through a litter bag experiment where pre-weighted fragments of P. decipiens and D. menziesii were sequentially removed from the drift line along 14days. Degradation of wrack biomass occurs within the first days of decaying, loosing up to 41.3% of its initial weight (D. menziesii), with remarkable variability among the two species tested. Higher feeding rates of amphipods were obtained with P. decipiens compared to that on D. menziesii, which can be mediated by its low content in deterrents and its blade shape, as well as being the most abundant species in the Deception Island and in many coastal areas of the Antarctic Peninsula. Globally, the consumer species assayed could process through consumption 0.73%day−1 of the instantaneous stock of algal deposits along the shore of Foster Bay. This study attempts to identify different linked processes poorly understood in the ecology of Antarctic shores, as the stranding, degradation and consumption of large amount of macroalgal subsidies from highly productive submerged rocky substrates toward low productive intertidal sedimentary shores. [Copyright &y& Elsevier]

Juvenile meagre were sampled at intervals during their first 500 days in a cage-based fish farm. Fish muscle showed a relatively low fat content (0.65-2.0%) when compared with other species of farmed fish, corroborating the consideration of meagre as a lean fish. At the beginning of the assay, saturated and mono- unsaturated fatty acids were in a similar proportion (approximately 30%), while polyunsaturated were close to 39% of total FAs, the n-3:n-6 ratio being of 3.8. Throughout the experiment a notable reduction in the sum of PUFA n-3 and an increase of linoleic (18:2n-6) and oleic acid (18:1n-9) was found. These changes led to a fall of n-3:n-6 ratio to values close to or lower than 1.0. Most probably, these changes reflect variations in the feeding regime applied during farming. In any case, fish offered good indices of lipid quality for human consumption. [ABSTRACT FROM AUTHOR]

Abstract: Studies on the digestive secretions in fish can elucidate certain aspects of their nutritive physiology and thereby resolve some nutritional problems, such as matching of an artificial diet to the nutritional needs of the fish. The aim of the present study was to analyse the digestive protease, amylase, and lipase activity in the Adriatic sturgeon and compare it with that of rainbow trout. The results show that the sturgeon is not only capable of digesting fat and protein, like any other carnivorous fish, but can also digest carbohydrates at levels characteristic of an omnivore. In turn, the proportion of acid-protease enzymes indicates the need for major gastric digestion. [Copyright &y& Elsevier]