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Summary The objective of these experiments was to determine juvenile sturgeon (Acipenser naccarii ) ability to capture live prey as well as to determine their feeding preferences when born and raised in captivity and fed on manufactured feeds until the commencement of the experiment. The purpose was to improve their nutrition and to aid in the development of restocking programmes. For the experiment, one non-adapted group (A) and one group (C, control) previously adapted for 10 days to live feed were used; each group comprised eight similar-age sturgeon (16 fish in total). The experiment was repeated four times for each specimen in group A (A1 to A4) and twice for each in group C (C1 and C2). Using aquaria of 40-L capacity in each experiment, each fish, in isolation, was provided with three individuals of each of the 12 prey categories tested. The number of attacks, differentiating between successful and unsuccessful, were counted, and the elapsed times until the first and third successes were measured together with the type of prey taken. During the course of the experiment, there was a significant reduction in the number of times required to achieve both the first and third successes, as well as a significant increase in the number of successes with time. Preferred prey were those of the worm type (Tubificidae and Lumbricidae). [ABSTRACT FROM AUTHOR]

The main objective of this study was to analyse differences and a similarities in morphometric characteristics among specimens of the same year class of Acipenser naccarii (Bonaparte, 1836), comparing fish raised either in Italy or Spain. All specimens were F1 of captive broodstock in Italy. Fifteen biometric variables were measured, and three derived indices were calculated, on 30 individuals of 3+ year class from Lombardy (Italy) and 90 individuals of 1+, 2+ and 3+ year class from Riofrío (Granada, Spain). A stepwise discriminate analysis (SDA) was carried out, and the results were contrasted using a non-hierarchical cluster analysis. The two groups proved to be similar, so a principal component analysis and a simple regression analysis were performed on all individuals, taking total length (Tl) as the independent variable and all the biometric variables as dependent. The study revealed that although the Soljan index (i.e. ratio of mouth width to snout length) is related to T1, and is a valid taxonomic characteristic, the CA index (i.e. relative position of the barbels) and FB index (i.e. ratio of snout length to width) are also valid characteristics for individuals longer than 57 cm, being independent of T1. [ABSTRACT FROM AUTHOR]

The sequence and timing of the embryonic development of Adriatic sturgeon (Acipenser naccarii) are described at a constant temperature (17±1 °C), from fertilisation to hatch in a hatchery. Fertilised eggs, obtained from one female and two males, were held in a flow-through system. On the first day, embryos were sampled every 20 min during the first 12 h, and every 40 min in the following 12 h. Embryos were sampled hourly on the second day. On the third and fourth days, embryos were sampled every 2 h, and every 3 h on the fifth and sixth days. The first cleavage furrow appeared at 1 h 40 min postfertilisation. Blastulation concluded at 12 HPF (hours postfertilisation), when the dorsal blastopore lip formed. The completion of gastrulation was at 18 HPF, closing of the neural tube at 23 HPF and formation of the s-shape heart at 31 HPF. The mass hatch occurred at 120 HPF. A. naccarii is a relatively common sturgeon species in aquaculture and possesses similar developmental patterns to those of other sturgeons; hence, we can use this species as a model for further studies about sturgeon species which are more difficult to breed artificially. Information about the embryonic development of the Adriatic sturgeon could assist restocking programmes. [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]

Abstract: In order to assess the metabolic organization of Acipenser naccarii, a representative species of the ancient ancipenserid chondrosteans, the activity of key enzymes of the main metabolic pathways in the liver, white muscle, and heart, as well as the levels of plasma and tissue metabolites of this sturgeon species have been evaluated and compared to those of the advanced teleost Oncorhynchus mykiss. In general, the epibenthic character of A. naccarii is reflected in the lower specific activity of most enzymes evaluated, in comparison to those of the more active O. mykiss. However, the metabolic organization of this sturgeon species shows some particularities that clearly differed from that of teleosts. Whereas the liver is the main gluconeogenic organ in rainbow trout, both the liver and white muscle of sturgeon possess the same capacity for glucose synthesis, with glycerol being the more suitable glucose precursor. Unlike teleosts, the liver is the main site for lipid storage in sturgeon which would be related to its lower capacity to transport metabolites involved in lipid metabolism. Although the capacity to transport free fatty acids (FFA) is lower in sturgeon than in trout, HOAD activity shows that this acipenserid is able to oxidize fatty acids in extrahepatic tissues such as the heart. Also, both sturgeon and trout showed the same hepatic capacity to oxidize fatty acids. The liver of sturgeon possesses a higher capacity to synthesize ketone bodies than trout which would be a primitive trait to export these compounds as fuels for peripheral tissues in order to offset the low ability to transport FFA in the blood. [Copyright &y& Elsevier]

Abstract: The digestive enzyme activities were determined in Adriatic sturgeon and rainbow trout during starvation and refeeding period. Overall, the digestive enzyme activities are affected in the same sense in both species. The protease and lipase activities were decreased later than amylase activity. Even after 1 month of starvation, both species would be prepared to digest protein and lipids in an effective way. After 72 days of starvation, the digestive machinery of the sturgeon and of the trout shows an altered capacity to digest macronutrients. The capacity to digest proteins and lipids, after 60 days of refeeding, begins to become re-established in sturgeon and trout. In contrast, in this period, the capacity to digest carbohydrates remains depressed in both species. [Copyright &y& Elsevier]

Abstract: Enzymatic antioxidant activities (superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase) and lipid peroxidation were determined in different tissues (gills, heart, digestive tract, liver, white muscle, skin, red blood cells, swimbladder) of trout (Oncorhynchus mykiss) and sturgeon (Acipenser naccarii). Total tissue antioxidant activity was, except for catalase, generally higher in trout than sturgeon, with the reverse tendency displayed by the liver. In both species, lipid peroxidation in the digestive tract showed higher values compared to the other tissues. Sturgeon, compared to trout, had higher energy content stored as fat in liver and muscle and thus appeared to have an effective safeguard against oxidation, as shown by low lipid peroxidation. [Copyright &y& Elsevier]

Abstract: Variations of Na+/K+-ATPase activity and fatty-acid composition in the gills of the sturgeon Acipenser naccarii subjected to progressive acclimation to full seawater (35 ppt) were determined in relation to the hypo-osmoregulatory capacity of this species in the hyperosmotic medium. Blood samples were taken and gills arches were removed at intermediate salinity levels between 0 and 35 ppt and after 20 days at constant salinity (35 ppt). Plasma osmolality and Na+/K+-ATPase activity increased significantly with growing environmental salinity. Total saturated fatty acids (SFAs) decreased, while total polyunsaturated fatty acids (PUFAs) increased significantly with increasing salinity due mainly to changes in n −3 PUFAs (20:5n −3 and 22:6n −3). The n −3/ n −6 ratio increased significantly during the acclimation process. The results show a direct relationship between salinity, increased gill Na+/K+-ATPase activity and ultrastructural changes of the gill chloride cells. Changes in the fatty-acid composition in gills of A. naccarii during progressive acclimation to full seawater suggest that variations of gill fatty acids may also have a role in osmoregulatory mechanisms. [Copyright &y& Elsevier]

The possible repercussions of osmoregulatory processes on some indicators of classical and oxidative stress were examined during gradual acclimation of sturgeons (Acipenser naccarii) to full seawater (35‰ salinity) and after a period of 20∼days at this salinity. Erythrocyte constants and levels of cortisol, protein and glucose in the plasma were determined. In addition, plasma osmolality and muscle-hydration values, as well as liver and heart protein, were determined. Catalase, glutathione peroxidase and superoxide dismutase activities and lipidperoxidation levels were measured in blood (plasma and red blood cells) and tissue (liver and heart). A number of physiological responses, such as disturbance in body fluid, activation of osmoregulatory mechanisms, augmented antioxidant defences in blood and alteration of energy metabolites, were detected with increasing environmental salinity. After 20 days at 35‰ salinity, plasma osmolality, erythrocyte constants and muscle water content all returned to values usual for low environmental salinity, indicating that osmoregulatory processes have achieved their objective. However, cortisol values, antioxidant enzyme activities in the blood (plasma and red blood cells), lipid peroxidation in plasma, and hepatic proteins did not return to initial values, showing that osmoregulatory processes cause major physiological changes in the fish. [ABSTRACT FROM AUTHOR]

Summary Ray-finned fishes display a spectacular range of evolutionary diversification, which is also reflected in their brain structure. Chondrosteans can be considered the most closely related extant taxa to the primitive actinopterygian fishes. However, current anatomical knowledge of the ontogenesis of the central nervous system of chondrosteans is scarce. In the present work, we studied the cytoarchitecture and gross morphology of the brain of the southern Europe autochthonous sturgeon Acipenser naccarii during ontogenesis. Nissl-stained serial paraffin sections of the brain of A. naccarii pre-larvae from day 1 after hatching to the transition stage to exogenous feeding to 90 days after hatching, were obtained. The five main brain divisions can be readily distinguished in 1-day-old specimens. The telencephalon of Acipenser develops by a process of eversion that can first be observed in 4-day-old larvae, although morphological changes in the telencephalon extend to very late in the development. With regard to the diencephalon, the epiphysis differentiates during the first days of development, but the outgrowth of the hypothalamic lobes occurs relatively late. During ontogenesis the mesencephalon maintains the embryonic tube-like shape, the tegmental portion differentiating much earlier than the dorsal or tectal portion. The cerebellum originates from two bilateral primordia; due to the fusion thereof, the medial portion of this area is transformed into a solid body which expands into the ventricular cavity of the brainstem. Finally, the rhombencephalon basal plate is strongly curved during the first days of development; later this curvature disappears and the dorsal walls of the rhombencephalon diverge, leading to the roof-plate transformation into a wide tela ependymalis. [ABSTRACT FROM AUTHOR]

Summary The present study maps the activity patterns of cytochrome oxidase (CO), a mitochondrial enzyme essential for oxidative phosphorylation, throughout the brain of the southern Europe autochthonous sturgeon Acipenser naccarii . The objective was to obtain detailed topographic knowledge on CO activity in the sturgeon brain at the light microscope level, which may reveal patterns of normal brain function, while serving as a baseline for subsequent comparison in studies on neural systems function, brain diseases, its development, plasticity, or aging. The CO histochemical staining intensity was quantified in 2-year-old specimens by optical densitometry of stained sections using a computer-assisted image analysis system; the standards were used to convert optical density into enzymatic activity. The CO activity was distributed in characteristic patterns and amounts that differed among various neural pathways, brain nuclei, cerebral layers, and neuron types. As in mammals, CO activity was relatively high in sensory and motor systems, but relatively low in the autonomic and visceral regulatory systems. [ABSTRACT FROM AUTHOR]

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]

The effect of both dietary lipid level and stocking density on digestive function was tested in young rainbow trout under culture conditions. Two dietary lipid levels (14 and 33%) and three culture densities (15, 30 and 40 kg/m 3 ) were assayed in triplicate lots: L14/D15, L14/D30, L14/D40, L33/D15, L33/D30 and L33/D40. Intestinal activities of amylase, lipase, trypsin, chymotrypsin, total protease (at different pHs) as well as some biometric parameters such hepatosomatic index (HSI) and digestivesomatic index (DSI) as indicative of perivisceral fat accumulation, were determined after a 12-weeks experimental period. A histological study of intestine was carried on to evaluate changes in tissue architecture. Fish fed on higher lipid diets grew more and accumulated a higher amount of fat in perivisceral tissue, although higher stocking density reduced this trend. According to digestive capacity, higher lipid intake induced an activation of lipase activity that was not apparent when fish were held under the highest rearing density. By other hand, dietary lipids promoted a significant inhibition of protease activity in fish under high density conditions. These results seem to indicate a clear interaction between both variables. In this study, it was manifested a general effect of dietary lipids level and culture density on digestive profile. These interactions should be taken into account when foreseeing the digestive utilization of a commercial feed at different culture conditions to improve fish production. [ABSTRACT FROM AUTHOR]

Early development of the Adriatic sturgeon Acipenser naccarii from its free embryo after hatching (stage 36), until late embryo stage, when the transition to exogenous feeding starts (stage 45) is described. Special emphasis is given to morphological development and description of the different structures that are formed at each life stage. After hatching, free embryos still present embryonic characteristics, little pigmentation and an ovoid yolk sac. The mouth begins to open on the second day post hatch (dph) and is fully open at 3 dph. The head begins to separate from the body at 4 dph and straightens at 6 dph. The first fins to appear are the pectoral fins on the yolk sac and an embryological fin fold that extends from behind the head to the posterior part of the yolk sac. All other fins will develop from this fold. At 7 dph the caudal fin begins to take a heterocercal form and dorsal scutes are observed. This study provides information that will assist aquaculturists by establishing a reference for the normal development of A. naccarii, which may be useful for evaluating the suitability and quality of fish produced for restocking. [ABSTRACT FROM AUTHOR]

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]

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]

The present study examines the particular metabolic strategies of the sturgeon Acipenser naccarii in facing a period of prolonged starvation (72 days) and subsequent refeeding (60 days) compared to the trout Oncorhynchus mykiss response under similar conditions. Plasma metabolites, endogenous reserves, and the activity of intermediate enzymes in liver and white muscle were evaluated. This study shows the mobilization of tissue reserves during a starvation period in both species with an associated enzymatic response. The sturgeon displayed an early increase in hepatic glycolysis during starvation. The trout preferentially used lactate for gluconeogenesis in liver and white muscle. The sturgeon had higher lipid-degradation capacity and greater synthesis of hepatic ketone bodies than the trout, although this latter species also showed strong synthesis of ketone bodies during starvation. During refeeding, the metabolic activity present before starvation was recovered in both fish, with a reestablishment of tissue reserves, plasmatic parameters (glucemia and cholesterol), and enzymatic activities in the liver and muscle. A compensatory effect in enzymes regarding lipids, ketone bodies, and oxidative metabolism was displayed in the liver of both species. There are metabolic differences between sturgeon and trout that support the contention that the sturgeon has common characteristics with elasmobranchs and teleosts. [ABSTRACT FROM AUTHOR]

Summary The present work examines the temporal appearance and degree of activity of digestive enzymes of pancreatic and intestinal origin (amylase as well as neutral and alkaline proteases) together with the evolution of the ontogenic development of the intestine and pancreas during the first month of free-living (30 days post-hatch-[dph]) of the sturgeon Acipenser naccarii. In addition, the influence of exogenous live feeding with Artemia salina on the detection of digestive enzymes was studied. Shown are that in the first life stages of the A. naccarii, from the time of fertilisation to the juvenile stage, the following events related to its digestive physiology occurred: digestive enzymes were detected in the embryo stage within the egg, presumably related to the hatching gland; in the free-living embryo stage, opening of the mouth was at 10 dpf and protease and amylase digestive activities occurred due to an early differentiation of the pancreas and intestine (12-13 dpf). At this stage, digestive enzymatic activities are partly owing to the live feed offered before disappearance of the yolk reserves (14 dpf); the expulsion of the melanin plug and the appearance of a continuity of the digestion tract (16 dpf) together with the disappearance of the yolk reserves (17 dpf) mark the passage from the free-living embryo phase to the juvenile stage; finally, from the first month after hatching in this sturgeon species, there is a stabilisation in digestive amylase and protease activities together with a fully developed digestive structure. The contribution of enzymes from prey in the detection of enzymatic activities determined in the fish was beyond doubt; therefore these exogenous enzymes must also have a certain physiological importance. Subsequent work will be needed to clarify the importance of digestive processes of the exogenous enzyme pool from live feed as well as to assess the possibility of shortening the weaning period. [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]

Abstract: A study has been made of the activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione reductase (GR), as well as of lipid peroxidation and of glutathione, during the first stages of ontogenic development of the sturgeon Acipenser naccarii: the embryo within the egg, the free embryo (with vitellin reserves), and the juvenile. Also, the same determinations were made in Artemia nauplii to determine the possible influence of the presence of live food in the quantification of the antioxidant-enzyme pool of the sturgeon. Activity was found for the antioxidant enzymes SOD, CAT, and GPX in all the stages of ontogenic development corresponding to the first month of life of the sturgeon A. naccarii. Notable activity of these enzymes was found during the embryonic phase. On the contrary, the GR activity was not detected in this phase, coinciding with a greater proportion of oxidized glutathione. In the sturgeon A. naccarii, after the embryo phase of free life, the activity of all the antioxidant enzymes tended to increase with age as did the glutathione levels. The results are compared with those previously determined in the different organs of the adult. The marked activity of the antioxidant enzymes found in the sturgeon A. naccarii during the first month of life provides the sturgeon effective protection against oxidative damage. [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]

This paper presents a sequential analysis of the development of the sturgeon (Acipenser naccarii) heart from the end of gastrulation to the early juvenile stages. At late neurulation, the heart appears as a straight, short tube located over the endoderm that forms the wall of the yolk sac, in front of the developing head. The heart axis is aligned with the axis of the developing head. Subsequently, the heart elongates and adopts a C-shape, and its axis becomes perpendicular to that of the head. Around the time of hatching, the heart loses the loop and appears as a mostly straight tube with the chambers arranged in a craniocaudal sequence: outflow tract, ventricle, atrium, and a small sinus venosus. During the first 4 days post-hatching (dph), the heart starts looping again, adopts a C-shape, and undergoes a counterclockwise movement that brings the atrium to the left of the outflow tract and the ventricle to a caudal position. Thus, a primary and a secondary cardiac loop occur in the sturgeon. Later, the atria come to occupy a middle position behind the outflow tract, and the sinus venosus shifts from a caudal to a dorsal position. A morphological arrangement similar to that found in adult sturgeons is attained in all specimens at days 7-9 dph. The external changes are accompanied by a series of internal modifications that include trabeculation (3-4 dph), development of endocardial cushions in the atrioventricular canal (4 dph) and in the conus arteriosus (3-4 dph), conus (22-24 dph) and atrioventricular (18-20 dph) valve formation, and development of the epicardium (4 dph) and the coronary vessels (10 dph). The main developmental features of the heart have been registered, and a basic body of information, which should be very useful in future developmental studies, has been established. Similarities and dissimilarities between the development of the sturgeon heart and that of other vertebrates are underscored. [ABSTRACT FROM AUTHOR]