Digestive enzyme activity during larval development of the Senegal sole (Solea senegalensis)

The activities of the main digestive enzymes (proteases, amylase, lipase) as well as those of acid and alkaline phosphatases were assessed during the larval development of the Senegal sole, Solea senegalensis. Important variations in specific activities of all the enzymes were observed during the period of study and were mostly related to the beginning or the end of metamorphosis. Both acid and alkaline protease activities were identified at early stages of development. Acid proteases accounted for only 10% of total protease activity in a 9 days-old larva, but exceeded 75% in a 33 days-old individual. Maximum lipase activity was related to the development of exocrine pancreas (days 6 to 10) and to metamorphosis. It is suggested this can be related to the metabolism of lipid reserves taking place during this morphological change. Activity of alkaline phosphatase decreased from day 5 to day 20 but therafter revealed a sharp increase, possibly linked to the development of enterocytes. The pattern of development of the main digestive enzymes found in S. senegalensis is similar to that described in other flatfish species.     

Changes During Chilled Storage of Whole Tilapia and Short-Term Frozen Storage of Tilapia Fillets

This study evaluated the physicochemical changes in Nile tilapia (n = 82, 373.71 ± 61.91 g) refrigerated for up to 92 h and in the frozen fillets. The tilapias were captured with nets, slaughtered by ice and water shock (1:1) in a temperature of approximately 2°C for 30 min, and stored refrigerated at 4°C in polystyrene boxes containing ice. The fish were filleted, and filets were weighed and frozen. The drip loss and protein were determined after 23 days of frozen storage. After 4 h of storage, all fish were in full rigor mortis. The pH of the muscles decreased for up to 45 h of the storage period. The fillets obtained from tilapia stored for more than 72 h lost more weight and protein. Thus, the filleting or processing of tilapia should be done before 72 h of cold storage, since deterioration of the fish starts to occur after this period.     

Effect of feeding time on dietary protein utilization and growth of juvenile Senegalese sole (Solea senegalensis)

The present study aimed to determine the effect of feeding time on growth and nitrogen excretion in juvenile sole. An 84‐day growth trial was conducted, in which food was supplied to three triplicate groups of juvenile Senegalese sole (3 g wet weight) at different schedules – diurnal, nocturnal and mixed. At the end of the growth trial, ammonia and urea excretion was assessed during a 24 h cycle. Improved growth (1.3% vs. 0.9% day^?1, specific growth rate), higher nitrogen retention (0.35 vs. 0.27 g N kg^?1 day^?1), lower ammonia excretion (209 vs. 272 mg N‐NH₄ kg^?1 day^?1) and lower total nitrogen excretion (278 vs. 352 mg N kg^?1 day^?1) were found in daytime‐fed fish compared with night‐fed fish. Fish in the mixed feeding regime showed intermediate values of ammonia and total nitrogen excretion, but did not differ from day‐fed fish regarding the other parameters. Results indicate that juvenile sole at a period of their life cycle appear to use more efficiently dietary protein for somatic growth under a diurnal than under a nocturnal feeding regime. This suggest that at least during a time‐window in the juvenile rearing a diurnal feeding regime might be more effective in the production of this species.     

Thermal habitat quality of aquatic organisms near power plant discharges: potential exacerbating effects of climate warming

Water temperature strongly affects aquatic ectotherms, as even slight temperature changes can have dramatic effects on physiological rates. Water bodies receiving industrial thermal discharges can undergo dramatic spatial and temporal changes in water temperature. To quantify effects on aquatic ectotherms, thermal habitat quality (bioenergetic growth rate potential; GRP) for zebra mussel, Dreissena polymorpha (Pallas), rusty crayfish, Orconectes rusticus (Girard), walleye, Sander vitreus (Mitchill) and smallmouth bass, Micropterus dolomieu (Lacepède) was estimated near two power plant thermal discharges on the Ohio River, USA, from 2010 to 2012 using bioenergetics models. These results were then compared with GRP under increased base temperatures representing climate warming. Growth rate potential for all species was low near the discharges during summer and highest in winter, with increasing prey consumption minimising the negative effects of increased temperatures. In their immediate vicinity, thermal discharges had a more adverse effect on GRP than plausible climate warming but primarily affected GRP over a small spatial area, particularly within 400 m downstream from the power plants. Examining thermal habitat suitability will become increasingly important as rising energy demand and climate change collectively affect aquatic organisms and their habitats.     

Towards a universal scale to assess sexual maturation and related life history traits in oviparous teleost fishes

The literature presents a confusing number of macroscopic maturation scales for fish gonads, varying from over-simplified scales comprising three to four stages to highly specific and relatively complicated nine-stage scales. The estimation of some important life history traits are dependent on a correct assessment and use of the gonadal maturation scales, and frequent mistakes have been made in many studies. The goal of this report is to provide a synthetic, relatively simple, yet precise maturation scale that works for most oviparous teleost fishes. The synthetic scale proposed here is based on the correspondence between key physiological and cytological processes of gamete development and corresponding modifications observed at the macroscopic level. It is based on previous and ongoing studies of several fish species pertaining to some of the most important African and Neotropical taxa, including Characiformes, Siluriformes, Osteoglossiformes and Perciformes. This scale should allow for standardized protocols of field studies and improve intra- and inter-specific comparisons of life history traits. Guidelines on the correct use of this scale to estimate these life history traits are provided.     

Effects of live feed containing Panagrellus redivivus and water depth on growth of Betta splendens larvae

Panagrellus redivivus is a nematode with a high protein content and low‐cost production. It is successfully used in the larviculture of shrimp, however, it has not yet been evaluated as feed for Betta splendens larvae. Thus, the objective of this study was to evaluate P. redivivus as feed for betta larvae maintained at different depths of water. The experiment was based on a completely randomized 3 × 2 factorial design, represented by two feed types and one alternating feeding regime plus two water depths (2.5 and 5.0 cm). The Artemia feed promoted the highest weight gain, followed by the alternating feeding regime. The single use of the nematode as live feed produced the poorest weight gain. The water depth and the feeding method influenced the specific growth rate (SGR). At a depth of 2.5 cm, the alternating feeding promoted similar SGR compared to fish fed with Artemia only. Furthermore, at the greater water depth an improvement in SGR was observed in fish fed Artemia only, but the similarity to alternating feeding regime remains. Thus, the inclusion of nematode is an appropriate and lower cost feed strategy for the betta larviculture independent of water depths.     

Moderate salinities enhance growth performance of Nile tilapia (Oreochromis niloticus) fingerlings in the biofloc system

The biofloc technology (BFT) has recently gained attention as an economic and environmentally sustainable system for aquaculture. The use of BFT with salinized water could be used to minimize the negative effects of nitrogenous waste and improve the growth performance of Nile tilapia. This work evaluated the growth performance, survival, gill lesions, and fillet composition of tilapia fingerlings (Oreochromis niloticus) reared during 70 days with different salinities (0, 4, 8, 12, and 16 g/L) in a biofloc previously developed. The results indicated that the use of mature bioflocs alone was sufficient to avoid fingerling mortality due to nitrite peaks. Moreover, the salinized water, especially between 4 and 8 g/L (maximum points around 6 g/L), can be recommended in BFT to improve the growth performance of tilapia in the initial culture phase. The salinity level that was evaluated did not affect fillet composition nor the occurrence of gill lesions. The total ammonia nitrogen concentration was lower in freshwater than in salinized water (p < 0.05). Nitrite peaks in salinities of 12 and 16 g/L appeared later and were higher in comparison to other treatments. Considering minimal water exchange in BFT, the use of salinized water in this system may be environmentally viable.     

Daily rhythms of cortisol and glucose and the influence of the light/dark cycle on anaesthesia in Nile tilapia (Oreochromis niloticus): Does the timing of anaesthetic administration affect the stress response?

Although daily variations in drug pharmacokinetics have been reported for a variety of teleost species, the influence of this daily variation on the cortisol response following anaesthesia remains poorly understood. To address this, two experiments were performed. The first experiment described the daily patterns of cortisol and glucose secretion in tilapia (Oreochromis niloticus). The second experiment investigated how the timing of anaesthetic administration (specifically at mid‐light [ML] or at mid‐dark [MD]) affects the induction and recovery times and plasma cortisol and glucose levels of juvenile Nile tilapia exposed to benzocaine, clove oil or tricaine methanesulphonate (MS‐222). The results revealed that the effect on the stress response associated with the moment when anaesthesia took place (ML or MD) varied according to the treatment (p < 0.05). Cortisol levels were significantly higher at ML for MS‐222 (ML = 116.23 ± 25.55; MD = 48.25 ± 22.33 ng/dl) (p < 0.05) and clove oil (ML 59.73 ± 14.27; MD 38.26 ± 12.07 ng/dl) (p < 0.05), whereas no significant differences were found between ML and MD cortisol levels for the control treatment (ML = 72.91 ± 18.42; MD = 64.80 ± 10.68 ng/dl) (p > 0.05) or in the benzocaine‐treated group (ML = 38.7 ± 4.90; MD = 38.60 ± 3.69 ng/dl) (p > 0.05). The highest plasma cortisol level in ML was found in the MS‐222‐treated group. All the tested anaesthetics had similar cortisol levels at MD (p > 0.05).     

Genetic population structure of black‐browed and Campbell albatrosses,and implications for assigning provenance of birds killed in fisheries

相似文献   

Effect of triploidy on muscle cellularity and flesh quality of turbot (Scophthalmus maximus)

Production of triploid turbot is a relevant goal for the aquaculture industry due to the benefits associated with their sterility and growth. In order for a better understanding of the final quality of the species, muscle cellularity and quality parameters of the flesh were studied in seven diploid and seven triploid turbot after sexual maturation. White muscle cellularity was evaluated throughout white muscle cross‐sectional area from the epaxial left muscle section of each fish. To ascertain the flesh quality, several physico‐chemical parameters (moisture, ash, protein, total fat, fatty acids and minerals) were analysed, and textural mechanical properties (springiness, hardness, chewiness, cohesiveness, gumminess and adhesiveness) were determined objectively with a texturometer. Muscle cellularity was different between both groups, such that muscle fibre density was higher for diploid specimens (P < 0.001) and muscle fibres diameters were higher for triploids (P < 0.001). Both ploidy groups showed no significant differences in moisture, ash, protein and total fat content (P > 0.05). All textural properties analysed showed no significant differences between both ploidy groups (P > 0.05). In both ploidy groups, fibre density and fibre diameter showed no significant correlations (P > 0.05) with textural parameters such as springiness, cohesiveness, chewiness and adhesiveness. Ploidy did not affect fatty acid composition, with the exception of eicosapentaenoic acid (C_20:5ω3) which was higher in the triploid group. No significant differences (P > 0.05) existed between diploid and triploid turbot in content of all minerals analysed. According to our results, the ploidy status determines significant variations on muscle cellularity but does not influence the flesh quality of the turbot.