The influence of different levels of dietary vitamin E on sea bass Dicentrarchus labrax flesh quality

Sea bass Dicentrarchus labrax fillet quality was investigated after feeding with four diets (A, B, C or D) containing different levels of dietary vitamin E (139 mg kg^–1, 254 mg kg^–1, 493 mg kg^–1 and 942 mg kg^–1, respectively). Six-hundred and eighty fish (mean initial weight 208 g) were equally divided into four 20 m³ tanks and fed for 87 days. Filtered seawater with a temperature ranging from 18.2 to 26.3 °C was supplied continuously. At the end of the experiment, fish were stored at 1 °C for 12 days. At one, three, six, nine and 12 days, 20 fish per group were processed for proximate composition, vitamin E and induced thiobarbituric acid reactive substances (TBARs) analyses. No significant differences in proximate composition were registered between groups. The flesh lipid content ranged from 88.0 g kg^–1 (group B) to 96.8 g kg^–1 (group A). Vitamin E fillet content was significantly different between groups, reaching levels of 98.0, 150.7, 225.2 and 302.0 μg g^–1 lipids for group A, B, C and D, respectively. Induced TBARs values were statistically different only for group A compared with the other groups. No significant variations were registered in relation to preservation time. Because of the positive influence of vitamin E on seafood quality and the correlation between its dietary level and flesh deposition, the α-tocopherol content of the diet should be well above fish minimum requirements.     

Response to T3 treatment and changing environmental salinity of liver lipid composition, mitochondrial respiration and (Na++ ++ K++)-ATPase activity in rainbow trout Oncorhynchus mykiss Walbaum

Rainbow trout Oncorhynchus mykiss Walbaum were fed a pelleted diet (14.3% wet weight lipid) containing 9 p.p.m. 3, 5, 3′‐triiodo‐l ‐thyronine (T₃) for 1 month and then transferred from fresh water to brackish water (average 22 p.p.t. salinity), where they were maintained untreated for 22 days. Trout fed a control diet were subjected to the same protocol. For both treated and control trout, liver lipid and fatty acid composition, mitochondrial respiratory activity and oxidative phosphorylation and (Na⁺ + K⁺)‐ATPase activity were monitored in fish sampled periodically throughout the trial. No differences between treated and control trout occurred in liver total lipid, phospholipid and cholesterol content or fatty acid composition. Conversely, irrespective of T₃ administration, the trout from the two habitats showed adaptive changes to salinity, differing in phospholipids and in the fatty acid composition of total and neutral lipids and selected phospholipids. Liver membrane permeability and mitochondrial respiratory activity were affected by both T₃ treatment and salinity transfer. The latter was apparently greater than the former in affecting mitochondrial respiratory activity. The higher (Na⁺ + K⁺)‐ATPase activity in T₃‐treated trout after 22 days in brackish water may reflect long‐term effects of the hormone linked to salinity adaptation.     

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.     

Fatty Acid Composition of Eggs and its Relationships to Egg and Larval Viability from Domesticated Common Sole (Solea solea) Breeders

The study of lipids and fatty acids (FAs) has been used in the assessment of egg quality because their composition can influence the fertilization rate, hatching, survival and growth of marine fish larvae. For these reasons, the lipid content (TL) and fatty acid composition of common sole (Solea solea) eggs were measured and correlated to egg and larval viability parameters throughout an entire reproductive season. Seventeen batches of fertile eggs obtained from natural spawning of captive breeders were characterized for the TL, FA profile, hatching rate (HR) and survival rate of larvae (SR) at 0–6 days post‐hatching (dph). The egg FA composition reflected the composition of the feed supplied to the broodstock during summer and autumn (before and during vitellogenesis) rather than that supplied during the spawning season. In general, the egg FA profile showed minimal differences among the early‐, mid‐ and late‐spawning periods (possibly due to the change of the diet and/or water temperature) indicating that it is possible to obtain a similar egg quality in terms of egg FA profile over 2 months of spawning. Saturated FAs and monounsaturated FAs (MUFA) were positively correlated with HR, while TL, 22 : 6n‐3 (DHA), 20 : 4n‐6 (ARA), polyunsaturated FAs of the (n‐3) series (n‐3 PUFA) and polyunsaturated FAs of the (n‐6) series were negatively correlated (p ≤ 0.05). MUFA, 20 : 5n‐3 (EPA), n‐6/n‐3 were positively correlated with SR, while DHA, n‐3 PUFA, DHA/EPA were negatively correlated (p ≤ 0.05). In conclusion, the feed supplied before and during vitellogenesis has a major role in determining the egg FA profile in common sole. The relationships found between TL and FAs with egg and larval viability parameters differ from many other farmed marine fish species, which may suggest the need for a specific broodstock feed for this species.     

Long‐chain PUFA enrichment in microalgae and metabolic dynamics in Tapes philippinarum larvae

The possibility of increasing n‐3 and n‐6 long‐chain polyunsaturated fatty acids (PUFA) content in microalgal mixtures used to feed Tapes philippinarum larvae was explored by lowering culture temperature from 26 to 14 °C. Although fatty acid composition of different microalgal species has a genetic basis, the algal cultures grown at 14 °C significantly increased the content of long‐chain n‐3 PUFA in Isocrysis galbana and in Thalassiosira pseudonana, while in Tetraselmis tetrathelo, the PUFA increase only involved shorter chain PUFA, namely 16:4n‐3 and 18:4n‐3. However, larvae fed on the PUFA enriched microalgal mixture did not show improvements in growth and survival performances with respect to the control group fed the microalgal mixture grown at 26 °C. From a biochemical perspective, two key aspects emerged from the results: (i) clam larvae have adequate biotransformation and selection skills to adjust fatty acid profile to their requirements as they can even modulate the incorporation of essential long‐chain PUFA as 20:5n‐3 and 22:6n‐3 when the dietary supply exceeds the physiological requirements; (ii) bivalve can biosynthesize non‐methylene‐interrupted dienoic (NMID) fatty acids as confirmed by the constancy of relative proportion with larvae growth in spite of the NMID fatty acid absence in the diet.     

Na,K-ATPase and Other Parameters in Bivalve Molluscs from the Adriatic Sea under Different Environmental Conditions

Veterinary Research Communications -     

Lipid composition and microsomal ATPase activities in gills and kidneys of warm- and cold-acclimated sea bass (Dicentrarchus labrax L.)

The response to cold of gill and kidney membrane lipid composition and microsomal (Na⁺+K⁺)-ATPase, Na⁺-ATPase and Mg²⁺-ATPase activities in reared sea bass (Dicentrarchus labrax L.) was investigated. Fish acclimation was carried out according to the seasonal cycle from August to March. No cold-promoted increase in fatty acid unsaturation was shown in gill and kidney polar lipids and in total lipids of mitochondria and microsomes. In both tissues the (Na⁺+K⁺)-ATPase exhibited positive compensation for cold acclimation whereas the Na⁺-ATPase displayed negative compensation. The Mg²⁺-ATPase showed no compensation in the gills and positive compensation in the kidneys. During cold acclimation the break in the Arrhenius plot of the (Na⁺+K⁺)-ATPase decreased, whereas breaks of both the Na⁺-ATPase and the Mg²⁺-ATPase activities remained unchanged. The results indicate that the sea bass does not adopt membrane unsaturation as a cold-facing strategy. The cold-promoted enhancement of (Na⁺+K⁺)-ATPase activity in osmoregulatory tissues may be advantageous to maintain efficient osmoregulation under thermodynamically unfavourable conditions.