Rodolfo Ballestrazzi

Salinity-dependence of the properties of gill (Na++K+-ATPase in rainbow trout Oncorhynchus mykiss

Abstract 1. 1. The expected higher gill (Na + +K + )-ATPase activity in rainbow trout adapted to brackish water (BW) with respect to fresh water (FW) is accompanied by some changes in the enzyme kinetics while the enzyme sensitivity to ouabain is unaffected 2. 2. Maximal activation is attained under the optimal conditions of 4 mM ATP, 7.5 mM Mg 2+ , 50 mM Na + , 2.5 mM K + , pH 7.0 in FW, and 3 mM ATP, 10 mM Mg 2+ , 100 mM Na + , 10 mM K + , pH 7.5 in BW. 3. 3. The change of the enzyme activation kinetics by Mg 2+ , ATP, Na + and K + from simple saturation in FW to cooperativity in BW and other habitat-dependent variations including the pH alkaline shift in BW are hypothetically related to an adaptive significance to the different environmental salinity. 4. 4. Gill total lipids and phospholipids are 30% lower in BW than in FW while their ratio is constant; some differences in gill total lipid fatty acid composition between FW and BW do not significantly affect the unsaturation parameters.

A preliminary histological and ultrastructural study of opercular anomalies in gilthead sea bream larvae (Sparus aurata) [Pagrus aurata].

The high prevalence of opercular deformities present in fish from Mediterranean marine hatcheries is an important problem, which is causing considerable economic losses. The aetiology of this syndrome is not yet well understood. In this study a histological and ultrastructural description of gilthead sea bream (Sparus aurata) larvae affected with anomalies of the opercular complex was carried out.Samples of larvae were obtained from a marine hatchery located in north-eastern Italy. For each sample, 100 larvae (age range day 0 to 90) were fixed for histological and ultrastructural observations. The first opercular alterations were detected 17 days after hatching, when the opercular support in the branchio-cranial area is still cartilaginous and the only structure of the opercle is a connective lamina composed of a dense connective tissue. Deformation could affect one or both opercles. No degenerative alterations or inflammatory processes were found in the opercular tissues.The electron microscopy (TEM) observations on 30 day old larvae allowed the identification of mineral deposition abnormalities within the dermal ossification in curled opercles. The mineralization process appears to be very heterogeneous and irregular, in some cases being less abundant than normally detected. These preliminary observations suggest that an early alteration in the connective tissue formation and an abnormal mineralization of the fibrous bone can predispose opercular folding.

The effect of dietary coconut oil on reproductive traits and egg fatty acid composition in rainbow trout (Oncorhynchus mykiss)

Two hundred and twenty rainbow trouts (IBW: 700 g) were randomly allotted to four tanks, with a male/female ratio of 0.56. Fish were fed for 168 d with four experimental diets containing herring oil, cod liver oil and coconut oil with the following inclusion rates: diet A: 12-1-0% respectively; diet B: 6-1-6%; diet C: 0-1-12%; diet D: 0-0-13%. Irrespective of the dietary treatment, weight gains of broodstocks were high (> 3 g/d) and FCR below 2. No significant difference was observed concerning the total amount of eggs spawn, egg average weight (82.5 mg/egg) and lipid content (5.4 mg/egg). However, the fatty acid profile of eggs was significantly affected by the dietary treatments. The content of unsaturated fatty acids, particularly the n-3 fatty acid series (EPA and DHA) significantly decreased with increasing levels of coconut oil in the diet.

The replacement of fish oil with refined coconut oil in the diet of large rainbow trout (Oncorhynchus mykiss)

Abstract Three hundred rainbow trout (242.9 ± 6.9 g) were randomly assigned to 12 fibreglass tanks (25 fish/tank). The fish were fed, for 231 days (feeding level: 0.74 % average bw), four experimental diets, containing increasing levels of coconut oil: diet A 0 %, diet B 6 %; diet C 12 % and diet D 13 %, as replacements of herring oil and cod liver oil. Weight gains of fish were > 3 g d-1 and FCR lower than 1.5, for all treatments. No significant difference was observed in the main carcass traits and whole body composition, but whole fish energy content significantly increased in fish fed diet D (10.68 KJ g-1). Different dietary fatty acid profiles had significant effects on the rainbow trout muscle contents of C10:0, C12:0, C14:0, total n-3, and the main ratios: SFA/USFA; DHA/EPA; DHA/AA, n-3/n-6, but not on total fatty acids content of the muscle.

Development and pharmacokinetic evaluation of erythromycin lipidic formulations for oral administration in rainbow trout (Oncorhynchus mykiss)

The aim of this work was to enhance the bioavailability of erythromycin base when administered orally in rainbow trout (Oncorhynchus mykiss). Since erythromycin is normally given in the form of medicated feed, in this study three new types of feed formulation were developed. A self-emulsifying system and two types of double microemulsions (O/W/O) were prepared, characterized and adsorbed on a commercial extruded diet for fish. The emulsified systems were based on saturated polyglycolized glycerides and mono- and diglycerides of medium-chain fatty acids (as oily phase), Tween 80 (as surfactant) and, in the case of double microemulsions, distilled water. The systems differed in percentage composition and for the amount and position of erythromycin in different phases. The three medicated feed were then administered orally by means of a gastric probe to rainbow trout and their relative bioavailability was estimated in comparison with that obtained after oral administration of feed with erythromycin powder. For each medicated feed, 80 fish were tested. Finally, plasma profiles of erythromycin after single administration of medicated feeds were used to predict profiles obtainable by administering once-daily medicated feeds for 7 consecutive days. The results proved that the feeds containing microemulsified erythromycin provided largely superior oral bioavailability and the advantage of obtaining the same efficacy against bacterial infections with a much lower dose of drug.

Response of rainbow trout gill (Na++K+)-ATPase and chloride cells to T3 and NaCl administration

With the aim of comparing the effects of oral T3 and NaCl administration on trout hypoosmoregulatory mechanisms, three groups of rainbow trout (Oncorhynchus mykiss Walbaum) held in freshwater (FW) were fed a basal diet (C), the same diet containing 8.83 ppm of 3,5,3′-triiodo-L-thyronine (T3) (T) or 10% (w/w) NaCl (N) respectively for 30 d. They were then transferred to brackish water (BW) for 22 d and fed on diet C. Gill (Na++K+)-ATPase activity and its dependence on ATP, Na+ and pH, number of gill chloride cells (CC), serum T3 level as well as fish growth, condition factor (K) and mortality were evaluated. During the FW phase, as compared to C trout, T trout showed a two fold higher serum T3 level, had unchanged gill (Na++K+)-ATPase activity and increased CC number, whereas N trout showed higher gill (Na++K+)-ATPase activity and CC number. At the end of the experiment the enzyme activity was in the order T>N>C groups and all groups showed similar CC number. Both treatments changed the enzyme activation kinetics by ATP and Na+. A transient increase in K value occurred in N group during the period of salt administration. In BW, T and N groups had higher and lower survival than C group respectively. Other parameters were unaffected by the treatments. This trial suggests that T3 administration promotes the development of hypoosmoregulatory mechanisms of trout but it leaves the (Na++K+)-ATPase activity unaltered till the transfer to a hyperosmotic environment.

Growth parameters in European sea bass (Dicentrarchus labraxL.): effects of live weight and water temperature

Abstract The voluntary feed intake (VFI) and growth rate of sea bass were studied for 147 days, based on different starting live weights, under natural photoperiods and varied water temperatures. Sea bass (n = 720) were divided into five weight classes (60–70, 90–110, 130–150, 160–180 and 230–250 g) and distributed among 20 tanks. Seven different water temperatures were compared: 13, 16, 19, 22, 25, 28 and 31 °C. A commercial extruded diet (N x 6.25, 43.7% DM; crude fat, 25.7% DM) was used. The trial was performed in a closed-circuit plant, with a daily water turnover rate of 10%. Each tank was fitted with an apparatus for collecting the uneaten food. Automatic feeders distributed equal amounts of food for ten meals per day. The daily food allowance was adjusted, based on fish biomass, to permit ad libitum feeding and to leave approximately 20% uneaten. Fish were exposed to natural photoperiod (March-July). Non-linear regression equations were used to calculate the best-fitting curves for the data.

Comparative study on milt quality features of different finfish species

Abstract The aim of this research was to study the main sperm characteristics of three different finfish species. Twenty-one gilt-head sea bream (Sparus aurata), 20 brown trout (Salmo trutta, morpha fario) and 15 rainbow trout (Oncorhynchus mykiss) male broodstocks, farmed under optimal conditions for each species and fed standard diets for broodstocks, were manually stripped. Brown trout yielded small amounts of sperm (4.5 vs 18.13 ml) that were very concentrated (≅ 8.5 x 109 vs 1.24 x 109 Szoa/ml) with respect to the other species. The duration of spermatozoan motility for gilthead sea bream sperm was significantly longer (almost 50 min), in comparison to the one-minute motility of Salmonids. Single fatty acids of brown trout sperm were higher than in the other two species for almost all detected fatty acids. In particular, eicosapentaenoic acid (EPA) was at least three times more concentrated in brown trout than in rainbow trout or gilt-head sea bream sperm (1238.3 µg/g vs 305.6 and 333.3 µg/g, respectively; P < 0.01). Saturated, polyunsaturated and total unsaturated fatty acid classes were significantly higher in brown trout sperm than in the other two species - almost double with respect to gilthead sea bream sperm and more than double in comparison to RT sperm (P < 0.01).

The control of reproduction in finfish species through GnRH treatments

Abstract Fish in captivity can show some dysfunctions, at different levels, in the physiological processes of reproduction, due to the lack of synthesis or release of gonadotropins (GtHs) by hypophysis. As a consequence, a worsening of quality and quantity of spawned gametes, or a lack of egg and sperm spawning, can be observed. The farmers can act on fish reproductive cycle manipulating the environmental parameters of rearing, the diet, the genetics or using GnRH treatments. Nowadays, they are used mainly GnRH, synthesized in laboratory as analogues. These releasing factors, naturally produced by hypothalamus, let to overcome the technological and biological limits of the “traditional” hormonal treatments with hCG, being more effective, cheaper and easily available on market. This article makes a historical survey of the conditioning treatments for fish reproduction and also considers the future perspectives of these treatments, examining the topics that research will have to focus, in order to make these treatments common worldwide, in any hatchery and for each farmed species of finfish.

Effects of vitamin E and phosphatidylcholine on qualitative and quantitative parameters of rainbow trout (Oncorhynchus mykiss) milt

Abstract The aim of this work was to investigate the effects of vitamin E and phosphatidylcholine on rainbow trout (Oncorhynchus mykiss) milt. One hundred and twelve rainbow trout (RB) broodstock (2n, 1030± 20g body weight, male:female ratio = 50:50) were fed four isoproteic and isolipidic diets for 110 days. Diets were differing for the type of vitamin premix and phosphatidylcholine supplied: Control (vitamin premix without Vit. E, no phosphatidylcholine); Vit.E (a premix with Vit. E, no phosphatidylcholine); PhC, (vitamin premix without Vit. E, phosphatidylcholine 2.5%); Vit.E +PhC, (vitamin premix with Vit. E and phosphatidylcholine 2.5%). Sperm total volume, in sexually mature males (3+; 966±114g body weight), ranged between 18.57ml (Control) and 34.31ml (Vit. E). Sperm density varied between 1.76x109 Szoa/ml (Control) and 1.16x109 Szoa/ml (Vit. E+PhC), while relative density (related to male body weight) tended to increase with Vit. E (>50x109 Szoa/ml) and to reduce with Vit. E + PhC (<30x109 Szoa/ml). Percentage motility was >85% in all treatments, while motility duration was around 2.37min for Vit. E and Control reached only 0.97min. After overnight storage (+4°C, for 18 hours) motility decreased, 75-80% in gamete motility and 3.39-56.7% in time motility. PhC dietary supplements significantly increased arachidonic acid contents of sperm with respect to Control (>120 vs 73µg/ g), while Vit. E caused a huge increase in C20:3 n-3 (10.25 vs 2.27ppm). DHA/EPA ratio was significantly lower in Control (>2; p<0.05), while n-3/n-6 ratio was significantly the highest for Vit. E (9.46 vs <7.3).