Optimal dietary protein levels in juvenile Senegalese sole (Solea senegalensis)

A study was undertaken to determine the dietary protein level for optimal growth performance and body composition of juvenile Senegalese sole. Five experimental extruded diets were formulated to contain increasing levels of protein [430, 480, 530, 570 and 600 g kg^?1 dry matter (DM)] and a constant lipid level, ranging from 100 to 130 g kg^?1 DM. Triplicate groups of 35 sole (initial body weight: 11.9 ± 0.5 g) were grown over 84 days in 60‐L tanks supplied with recirculated seawater. Fish were fed by means of automatic feeders in eight meals per day. At the start and end of the trial, whole‐body samples were withdrawn for proximate composition analysis. At the end of 84 days of experimental feeding, daily weight gain and specific growth rate in fish fed diets P43 and P48 were significantly lower than those found in fish fed higher protein level diets (P53, P57 and P59). Similarly, feed efficiency was also significantly lower in fish fed diet P43 than in fish fed all other dietary treatments. Sole juveniles fed lower protein level diets (P43 and P48) showed a significantly lower protein content than fish fed the higher dietary protein level treatments (P53, P57 and P60). Changes within the tested dietary protein levels did not affect significantly protein productive value or total nitrogen (N) losses in fish. However, daily N gain was significantly higher (P < 0.05) in fish fed diets P53 and P60 than in fish fed the lowest protein level diet (P43). Data from the present study indicate that diets for juvenile Senegalese sole should include at least 53% crude protein to maintain a good overall growth performance. Based on a second‐order polynomial regression model, the daily crude protein requirement for maximum whole‐body N gain as estimated here for Senegalese sole juveniles was 6.43 g kg^?1 body weight day^?1 which corresponds to a value of 1.03 g N intake kg^?1 body weight day^?1. If the present data are expressed on a dietary crude protein concentration basis, the allowance for maximum protein accretion (N gain) would be met by a diet containing a crude protein level of 600 g kg^?1.     

Antimicrobial activity in bacteria isolated from Senegalese sole, Solea senegalensis, fed with natural prey

Intestinal bacteria in marine fish may produce antimicrobial substances which inhibit pathogenic bacteria. The aim of this study was to determine the influence of a change of fish diet on the antimicrobial activity of the culturable aerobic gut microflora of Senegalese sole, Solea senegalensis. Pre‐adult 15‐month‐old fish previously fed on an artificial diet, were fed polychaetes (Hediste diversicolor), which form part of the natural diet of Senegalese sole. Samples were taken0, 3 and 6 weeks after start of the experiment from the stomach, small and large intestine of the fish. The bacterial strains isolated from these samples were sub‐cultured to pure cultures and stored at ?80°C. Several biochemical tests were run to obtain some basic phenotypic characteristics of the isolated strains. Amplification and sequencing of 16S rDNA fragments were used to identify the majority of the bacterial strains isolated. The identification by use of this molecular approach gave results in agreement to the phenotypic characterization. Feeding with polychaetes significantly increased (P<0.05) the numbers of presumptive Vibrio isolates in the gut. The number of bacterial strains with antimicrobial activity, as determined by two in vitro approaches, was significantly (P<0.05) increased by feeding with polychaetes.     

Rearing temperature affects Senegalese sole (Solea senegalensis) larvae protein metabolic capacity

The present work examined the short- and long-term effects of three rearing temperatures on protein metabolism and growth trajectories of Senegalese sole larvae using ¹⁴C-labelled Artemia protein as feed. A first feeding trial was performed on larvae reared at 15, 18 and 21 °C (at 26, 17 and 14 days post-hatching (dph), respectively) and a second trial conducted on post-larvae after transfer to the same rearing temperature (~20 °C) (49, 35 and 27 dph, in larvae initially reared at 15, 18 and 21 °C, respectively). Temperature greatly influenced larvae relative growth rate (RGR) and survival, since growth at 15 °C was severely depressed. Protein digestibility and retention was highest at 18 °C during the first trial (85.35 ± 1.16 and 86.34 ± 2.33 %, respectively). However, during the second trial, post-larvae from 15 °C had the highest feed intake and protein digestibility (3.58 ± 1.54 and 75.50 ± 1.35 %, respectively), although retention was similar between treatments. Furthermore, after transfer to 20 °C larvae from 15 °C experienced compensatory growth, which was observed until 121 dph, and confirmed by RGR values, which were significantly higher at 15 ºC than at 21 ºC or 18 ºC. Results from the present study show that Solea senegalensis larval development, survival and protein digestion and retention are highly affected by thermal history.     

Intestinal microbiota variation in Senegalese sole (Solea senegalensis) under different feeding regimes

The aim of this study was to determine the influence of the feeding regimes in Senegalese sole (Solea senegalensis) cultured under extensive, semi‐extensive and intensive production systems. A total of 254 bacterial isolates from guts of fish cultured under different production systems and feeding regimes were tested. Biochemical tests and genetic analyses based on the 16S rDNA sequence analysis were conduced to identify bacterial strains. Vibrio species were the most represented taxonomic group in the culturable microbiota of S. senegalensis guts tested. Particularly, Vibrio ichthyoenteri was the most frequently isolated Vibrio species. Comparison among diets showed a significant reduction (P<0.05) in vibrio percentages and a higher occurrence of Shewanella species in Senegalese soles fed polychaeta. In addition, a major influence of environmental temperature on microbiota composition was detected. Cold temperatures brought about a change in the percentages of Vibrio species and a higher representation of α‐Proteobacteria in both outdoor systems (extensive and semi‐extensive). The significant differences between intestinal bacterial composition in Senegalese soles fed commercial diets and natural preys (polychaeta) reveal the necessity to develop specific optimized diets for the intensive rearing of this fish species.     

Feed deprivation in Senegalese sole (Solea senegalensis Kaup, 1858) juveniles: effects on blood plasma metabolites and free amino acid levels

The effects of prolonged feed deprivation were assessed on blood plasma metabolites and free amino acid levels in Solea senegalensis. Juvenile specimens were maintained at two experimental conditions (24 h fasted and 21 days feed-deprived). In feed-deprived fish, relative growth rate and hepatosomatic index as well as plasma triglycerides and proteins levels were significantly lower. However, plasma cortisol levels were higher in feed-deprived fish, while plasma glucose and lactate values were not significantly different between treatments. Furthermore, feed-deprived fish showed higher levels of total plasma free amino acids than 24 h fasted fish. In 21 days feed-deprived sole, an increase in plasma cortisol levels may suggest a functional role in mobilizing energy due to the catabolic action of this hormone in teleosts. Higher levels of glutamine, arginine and ornithine in 21 days feed-deprived fish may be indicative of a dual role for these amino acids: ammonia detoxification and carbon source for gluconeogenesis. The increased plasma glucogenic and branched-chain amino acid levels, together with the maintenance of plasma glucose in 21 days feed-deprived sole, suggest active liver gluconeogenic processes supported by tissue proteolysis.     

Use of probiotic bacteria in the rearing of Senegalese sole (Solea senegalensis) larvae

Three candidate probiotics, which had shown antimicrobial activity in vitro against two fish pathogens, were used in the rearing of Senegalese sole larvae and postlarvae. These probiotics improved the survival of starved sole yolk‐sac larvae. A feeding experiment of sole larvae and postlarvae comprised three treatments: A, B and C. Cultures of a Vibrio sp. (2J18) were added to treatment A, whereas a gram‐positive (J84) and a Shewanella sp. strain (2J27), were added to treatment B, while in a control treatment C no bacteria were added. Addition of bacteria in treatment B increased survival of larvae in the first phase of the experiment [0–20 days after hatching (DAH) (P<0.05)] and decreased the numbers of colony‐forming units (CFU) in larval gut 5 DAH compared with the control treatment (P<0.05). No differences were observed in survival (25–47%) during the second phase of the experiment (20–60 DAH). Nevertheless, the total numbers of CFU in fish gut 40 DAH were significantly lower in treatment B (P<0.05). The colonization rates of the added bacteria were the highest 5 and 11 DAH, and the highest average values reached were 65%, 82% and 17% of the total CFU count for the strains 2J18, 2J27 and J84 respectively.     

Immunohistochemical diagnosis of tenacibaculosis in paraffin‐embedded tissues of Senegalese sole Solea senegalensis Kaup, 1858

A sensitive and specific immunohistochemical technique was developed to improve the diagnosis of tenacibaculosis and to better understand its pathogenesis. Senegalese sole Solea senegalensis Kaup, 1858 were inoculated subcutaneously with a bacterial suspension of Tenacibaculum maritimum, and samples were taken at different hours post‐inoculation. Sections from different organs were used as positive controls. In addition, a total of 128 field samples from different organs collected from tenacibaculosis outbreaks were used. Tenacibaculum maritimum antigens were detected in several organs of experimentally infected Senegalese sole and in at least one of the tissues from fish suffering from natural tenacibaculosis previously confirmed by culture and PCR‐based methods. In fish collected during outbreaks, a strong positive reaction was detected in ulcerative skin areas. Moreover, bacterial antigen was identified inside scale pockets and in sites of the skin with mild lesion. In kidney and spleen, evident immunostaining of bacterial antigen was detected in both naturally and experimentally infected fish. Besides, the presence of T. maritimum in the intestinal tract without associated histological changes suggests that this organ may act as a reservoir for T. maritimum. The results of this study confirm the usefulness of IHC for the diagnosis of tenacibaculosis in paraffin‐embedded tissues.     

Physiological short-term response to sudden salinity change in the Senegalese sole (Solea senegalensis)

The physiological responses of Senegalese sole to a sudden salinity change were investigated. The fish were first acclimated to an initial salinity of 37.5?ppt for 4?h. Then, one group was subjected to increased salinity (55?ppt) while another group was subjected to decreased salinity (5?ppt). The third group (control group) remained at 37.5?ppt. We measured the oxygen consumption rate, osmoregulatory (plasma osmolality, gill and kidney Na⁺,K⁺-ATPase activities) and stress (plasma cortisol and metabolites) parameters 0.5 and 3?h after transfer. Oxygen consumption at both salinities was higher than for the control at both sampling times. Gill Na⁺,K⁺-ATPase activity was significantly higher for the 55?ppt salinity at 0.5?h. Plasma osmolality decreased in the fish exposed to 5?ppt at the two sampling times but no changes were detected for high salinities. Plasma cortisol levels significantly increased at both salinities, although these values declined in the low-salinity group 3?h after transfer. Plasma glucose at 5?ppt salinity did not vary significantly at 0.5?h but decreased at 3?h, while lactate increased for both treatments at the first sampling time and returned to the control levels at 3?h. Overall, the physiological response of S. senegalensis was immediate and involved a rise in oxygen consumption and plasma cortisol values as well as greater metabolite mobilization at both salinities.     

Feed intake and growth performance of Senegalese sole (Solea senegalensis Kaup, 1858) fed diets with partial replacement of fish meal with plant proteins

To be able to study nutrient requirement and utilization in any species, a diet supporting normal feed intake and growth equally well as a traditional fish meal‐based diet is needed. Additionally the formulation of the diet should allow low levels of the nutrient under study. When studying the amino acid metabolism and requirements, one cannot rely on the fish meal‐based diets as fish meal are nicely balanced according to requirements. Therefore the current study aimed to develop a plant protein‐based diet (with low fish meal inclusion) to be used in the nutritional studies of Senegalese sole juveniles supporting feed intake and growth close to that obtained in a fish meal‐based control feed. Two experiments were conducted to evaluate whether Senegalese sole juveniles would accept and utilize diets containing high plant protein inclusion. For testing the acceptance of high plant protein inclusion, two diets were formulated: a reference diet that contained fish meal as the main protein source (450 g kg^?1 dry matter) whereas in the test diet, fish meal was substituted by a mixture of plant ingredients (soybean meal, corn and wheat gluten) with l ‐lysine supplementation. In order to improve the palatability, 50 g kg^?1 squid meal was added to both diets. The indispensable amino acids (IAA) profile of the test diet was made similar to the control diet by adding crystalline amino acids. Further, automatic feeders were used to improve the feed intake. Fish (24 g initial body weight) were fed the diets for a period of 4 weeks. As fish accepted both diets equally well, a second study was undertaken to test the growth performance. Fish (6 g initial BW) were fed the diets for a period of 12 weeks. The use of automatic feeders to deliver the feed and the addition of both squid and balancing the indispensable amino acids resulted in growth performance and accretion not differing from the fish meal fed control. It can be concluded that juvenile Senegalese sole are able to grow and utilize high plant‐protein diets when both diet composition and feeding regime are adequate for this species.     

Influence of tank bottom surface on growth and welfare of Senegalese sole (Solea senegalensis)

Tank bottom surface is an important question to take into account in flatfish aquaculture considering the intimate contact that the fish have with it. The most usual materials in aquaculture tank surfaces are inert materials such as epoxy resins or plastics with null porosity, and cement that presents a high alkalinity, roughness and porosity. To improve the cement characteristics, silica fume admixture is usually added in construction industry. The aim of this study was to evaluate the effect of three types of tank bottom surfaces on growth and welfare over a Solea senegalensis population. Moreover, the degree of fin erosion, the appearance of skin lesions and malpigmentation patterns were also monitored. The bottom surfaces tested were plain cement (CE), the same plain cement blended with silica fume (10%) (SF) and epoxy coated surface (EP). Specific growth rate for each bottom surface were compared. The Image Processing Activity Index (IPAI) was used to evaluate the Senegalese sole welfare. Higher SGR and lower IPAI values were obtained in the surface of cement with silica fume, suggesting a higher welfare. The use of plain cement affected negatively the performance of fish, probably due to the high pH and alkalinity of the water in direct contact with fish skin. The null porosity of EP seems to be related to the main cause of higher activity level of fish kept on it outcoming in lower growth. Silica fume that is frequently use to improve the mechanical characteristics of plain cement, also provides benefits in terms of fish welfare.     

New insight on vertebral anomalies in cultured Senegalese sole (Solea senegalensis,Kaup) at early stages of development

Senegalese sole (Solea senegalensis, Kaup) is a promising flatfish species in aquaculture. However, skeletal anomalies are still a great concern in sole farming. Investigation of this issue is crucial to improving larval quality and optimizing production. The aim of this study was to thoroughly assess anomalies in the rachis of reared sole at early developmental stages. Sole (n = 507) were sampled at 31 or 32 days after hatching (dah). The specimens were stained with alcian blue and alizarin red and evaluated for the detection of vertebral deformities. Most fish presented 9:34:3 vertebrae in abdominal, caudal and caudal complex regions, respectively. Remarkably, all specimens showed at least one spinal anomaly. Alterations of neural/haemal elements, as well as deformities of hypurals, parhypural and epural, were recurrent. Vertebral body anomalies and/or vertebral column deviations were identified in 52% of the individuals. Vertebral deformations and fusions were common, especially in caudal complex. ‘Minor’ anomalies were predominant, and some of the detected disorders might be a result of non‐/low‐pathological processes. These results contribute a new insight into the main skeletal anomalies affecting cultured sole larvae. Further research is required to determine their impact on fish welfare and external appearances at commercial stages.     

Selenium supplementation changes glutathione peroxidase activity and thyroid hormone production in Senegalese sole (Solea senegalensis) larvae

Dietary selenium (Se) influences the glutathione peroxidase (GPx) activity and the thyroid hormone system in vertebrates, but these relations are poorly described in fish. The present study aimed to evaluate the effect of Se supplementation on Senegalese sole larvae, focusing on GPx activity and thyroid status. Two groups of larvae were fed on either control (C) or Se‐enriched live feed, from 2 days after hatch (DAH) until 34 DAH. Senegalese sole larvae fed Se‐enriched live feed significantly increased their whole‐body Se, compared to larvae from C group. The activity of GPx was higher in larvae from Se group, suggesting that the levels of this mineral were suboptimal in the control diet. TH levels were also higher in larvae fed Se‐enriched live feed, suggesting that Se may have a positive influence on the TH production in early life stages of marine fish larvae.     

Immune responses and gut morphology of Senegalese sole (Solea senegalensis,Kaup 1858) fed monospecies and multispecies probiotics

The current study aimed to determine the effects of dietary probiotic supplementation on growth, gut morphology and non‐specific immune parameters in Senegalese sole (Solea senegalensis) juveniles during a 1‐month trial. Fish were fed for 1‐month two diets with 1.0 or 4.6 × 10⁶ CFU kg^?1) of probiotic A (Bacillus sp., Pediococcus sp., Enterococcus sp. and Lactobacillus sp.) and two diets with 3.5 or 8.6 × 10⁵ CFU kg^?1 of probiotic B (Pediococcus acidilactici) and tested against an unsupplemented diet (control). Growth performance, as well as respiratory burst activity, nitric oxide (NO), alternative complement pathway (ACH50), lysozyme and peroxidase activities, was not affected by the dietary treatments. Probiotic supplementation tended to increased growth homogeneity between tanks having diet A₁ the best possible alternative to decrease costs associated to size grading. Villous length and number of goblet cells of the anterior intestine did not vary among treatments. Muscle duodenal layer was significantly thicker in fish fed probiotic A compared to probiotic B, when included at the lowest level (A₂ versus B₂). The current study indicate that the use of the multispecies probiotic at 1.0 × 10⁶ CFU kg^?1 might enhance protection against pathogen outbreak and increase nutrient absorption, whereas at the highest concentration could reduced size dispersion among tanks.     

Water temperature does not affect protein sparing by dietary carbohydrate in Senegalese sole (Solea senegalensis) juveniles

The effect of dietary protein reduction balanced by an increase in carbohydrate (starch) level on growth performance, feed utilization and intermediary metabolism of Senegalese sole juveniles was evaluated at two temperatures, 12 and 18°C. For that purpose two isolipidic (16% lipids) diets were formulated to contain 550gkg^?1 protein and 90gkg^?1 starch (diet HP:LC), and 450gkg^?1 protein and 200gkg^?1 starch (diet LP:HC). Each experimental diet was fed to triplicate groups of 20 fish (initial body weight: 15.9g) within each temperature. Diets had no effect on growth and feed utilization. Temperature affected growth but not feed efficiency, with fish growing more at 18°C. Fatty acid synthetase and glutamate dehydrogenase activities were higher at 12°C than at 18°C while activity of the other measured enzymes was not affected by water temperature. Glucokinase and malic enzyme activities were lower while fructose 1,6‐bisphosphatase activity was higher in fish fed the HP:LC diet. Our data suggest that protein can be reduced from 550 gkg^?1 to 450 gkg^?1 by increasing starch level in high lipid diets for Senegalese sole juveniles without affecting overall performance. A reduction in protein content through an increase in dietary starch decreases hepatic gluconeogenesis. Increasing temperature from 12°C to 18°C improves fish growth but does not affect feed efficiency.     

Effect of dietary protein level and source on digestive proteolytic enzyme activity in juvenile Senegalese sole, Solea senegalensis Kaup 1850

The effect of dietary protein level and protein source on growth and proteolytic activity of juvenile Solea senegalensis was studied. In Experiment 1, fish were fed on four experimental diets containing increased protein levels (36, 46, 56 and 67%). In Experiment 2, Senegalese soles were fed on five diets with partial substitution of fish meal by soybean meal, soybean protein concentrate, soybean protein isolate, wheat gluten meal or pea protein concentrate. Results prove that growth and proteolytic activity in the distal intestine of fish were affected by the quantitative increase in dietary protein. The origin of protein source used in the elaboration of experimental diets affected both the amount and composition of the alkaline proteases secreted into the intestinal lumen; however, it did not decrease animal growth. Juvenile Senegalese sole showed capability to modulate digestive protease secretion when the concentration and/or source of dietary protein were modified. Quantity and quality of dietary protein affected protein hydrolysis in Senegalese sole intestine. This study establishes that 30% fish meal protein can be replaced by soybean derivatives without affecting intestinal proteases. Replacement with wheat gluten meal or pea protein concentrate should be taken cautiously, but further research is needed to establish whether growth performance and digestive enzyme physiology of Senegalese sole are affected by plant protein-supplemented diets in a long-term trial.     

塞内加尔鳎养殖研究进展

塞内加尔鳎分布于地中海及大西洋沿岸南部,在西班牙和葡萄牙养殖普遍。我国2003年引进,2005年人工繁殖成功。目前,国内塞内加尔鳎的价格极高,鱼种每尾30~40元。塞内加尔鳎适合我国中部以北大部分地区养殖,发展前景广阔。影响塞内加尔鳎养殖发展的主要瓶颈是缺少技术。塞内加尔鳎在我国的养殖尚处在技术探索阶段。介绍了国外养殖塞内加尔鳎技术及最新研究成果。