The effect of different carotenoid sources on skin coloration of cultured red porgy (Pagrus pagrus)

This study presents data on the effect of carotenoid sources on skin coloration of red porgy (Pagrus pagrus). Three experiments were conducted: in the first, fish were fed an astaxanthin (Naturose^®)‐supplemented diet, while the second fish received diets supplemented with β‐carotene (Rovimix β‐caroten^®) or lycopene (Lyc‐O‐Mato^®): Carotenoids were added to the level of 100 ppm in each diet, while a non‐carotenoid‐supplemented diet served as a control. In the third experiment, the effect of dietary protein/carbohydrate ratio on melanin content in the skin was investigated. For this experimentation, four diets were formulated to contain 50/23, 40/32, 30/48 and 20/59 protein/carbohydrate ratio. Naturose^® astaxanthin increased total carotenoid content in the dorsal skin area while β‐carotene and lycopene seem to have had no significant effect. Naturose^® was the only carotenoid source that had a significant effect on skin hue, promoting a reddish coloration to the dorsal skin area and a ventral hue similar to wild red porgy. No apparent effect of carotenoid source on skin melanin content was observed. In contrast, dietary protein/carbohydrate ratio affected melanin content in the skin. The fish fed the 50/23 diet showed significantly higher values. Farmed red porgy had eight times higher dorsal‐skin melanin content than wild ones.     

Environmental control of skin colour in the red porgy, Pagrus pagrus

Fish display sophisticated skin chromatic properties that are of considerable ecological, physiological and behavioural importance. The aim of study was to investigate the role of important physical parameters (background colour, lighting spectrum, light intensity and water temperature) on skin colour to gain better knowledge of the environmental factors that regulate pigmentation in cultured red porgy, Pagrus pagrus . All tested physical parameters had a significant effect on skin lightness, especially in the dorsal body area; low light intensity, blue spectrum, a water temperature of 19 °C and a white background significantly increased skin lightness. This effect was mediated through changes in melanophore motility and/or skin melanin concentration. None of the examined factors affected skin hue while a significant decrease in skin entire colour index (a combination of hue and chroma) was found only in white background-adapted fish. It is concluded that all tested physical factors are important regulators of skin lightness.     

First report of Streptococcus iniae in red porgy (Pagrus pagrus, L.)

This work describes the first isolation of Streptococcus iniae in red porgy, Pagrus pagrus (L.), and the first European isolation of this pathogen in gilthead seabream, Sparus aurata (L.). In both farmed fish species, infection resulted in lethargy, anorexia, abnormal swimming, exophthalmia and sudden death, with mortality rates of over 25% in red porgy and 10% in gilthead seabream. Beta-haemolytic Gram-positive cocci, catalase negative and oxidase negative, were isolated in pure culture from internal organs. Conventional and rapid identification systems, and 16S rRNA gene partial sequencing were used to identify the causative agent of the natural disease. LD50 trials were carried out to show the virulence of this isolated strain in these species, with values of 1.7 × 104 CFU per fish in red porgy and 1.32 × 105 CFU per fish in gilthead seabream. The most prominent lesions were meningoencephalitis and multifocal infiltration of macrophage cells in the kidney and spleen.     

Seasonal changes in sperm production and quality in the red porgy Pagrus pagrus (L.)

Cultured red porgy Pagrus pagrus (L.) males (n=6) were sampled every 2 weeks for milt, in order to monitor changes in sperm quality parameters during a whole spawning period. On 11 January 2001, 60% of the fish were spermiating, increasing to 100% in mid‐February and dropping to 30% by mid‐April. Sperm density showed a slight increasing trend, with mean values ranging between 8.6 and 23.7×10⁹ spermatozoa mL^?1. Sperm motility percentage exhibited a significant improvement during the spawning season (analysis of variance (anova ) P=0.0001). The duration of forward motility for the major part of the monitoring period ranged between 2 and 4 min. Red porgy spermatozoa maintained their viability for many days after whole storage of milt at 4°C. During the monitoring period there were significant changes in the mean duration of sperm survival after cold storage, ranging from 5 to 12 days. The total volume of expressible milt was maximal on 28 March, increasing from a mean value of 1.7 mL to 5.3 mL kg^?1. Milt production of captive‐reared red porgy does not appear to be limiting, when compared with the volume of expressible milt produced by other cultured marine fishes.     

Dietary carotenoids and skin melanin content influence the coloration of farmed red porgy (Pagrus pagrus)

The present study investigates the effects of dietary carotenoid sources on the coloration of the red porgy, Pagrus pagrus. Red porgies (131.9 ± 16.2 g; mean ± SD) were fed for 12 weeks on five different diets supplemented with red carotenoids (mainly astaxanthin esters) supplied from Haematococcus pluvialis algae and yellow carotenoids (mainly β‐carotene, lutein, and zeaxanthin) supplied from Alfalfa, Medicago sativa L. and Spirulina, Spirulina pacifica. The carotenoid‐supplemented diets did not have any marked effect on the growth rate, the feed conversion ratio, the daily feeding rate, or the hepatosomatic index of red porgy. The biochemical indices measured in plasma including cholesterol, total proteins, glucose, lactate, phospholipids, non‐esterified fatty acids, triglycerides, and thyroid hormones did not differ significantly among groups. Diet did not affect significantly the melanophore‐area coverage, the melanin skin concentration and skin lightness. Carotenoid‐supplemented diets affected significantly the carotenoid deposition in the skin, the presence and distribution of erythorphores and xanthophores, and skin hue and chroma. Overall, data have shown the efficacy of Haematococcus algae in promoting a reddish coloration in red porgy.     

Digestive enzyme activity of the red porgy (Pagrus pagrus, L.) during larval development under culture conditions

The ontogenic development of the main digestive enzymes (proteases, amylase and lipase) in the red porgy, Pagrus pagrus, larvae was assayed during the larval development. The green water technique was carried out for larval rearing and whole‐body homogenates were used for enzymatic assays in triplicate. Significant alterations in specific activities of all digestive enzymes measured during the period of this study were mostly related to metamorphosis and weaning. Trypsin‐ and chymotrypsin‐specific activities were first detected on day 3, together with opening of the mouth, and slightly increased until 25 days after hatching (DAH). After this period, the specific activities of these enzymes slightly decreased. Pepsin was first detected on day 28, concurrent with stomach formation, and a sharp increase was observed until 30 DAH. A slight decrease was measured from this date until the end of the experiment. Both amylase and lipase were measured for the first time on days 2 and 4 respectively, and the specific activities of these enzymes showed similar patterns during the first week of the study. Then, slight variations were observed until 30 DAH and while lipase‐specific activity declined, an increase in the specific activity of amylase was found until the end of the experiment. It is concluded that the variations observed in the specific activity of digestive enzymes were related to either metamorphosis, such as the formation of the stomach (28 DAH), or to changes in food composition. The profile of the developmental pattern of the main digestive enzymes detected in P. pagrus is similar to that described for other Sparid species.     

Separate and combined effects of cyclic fasting and l‐carnitine supplementation in red porgy (Pagrus pagrus,L. 1758)

We examined the effects of cyclic fasting in red porgy (Pagrus pagrus) fed different dietary carnitine levels. Juvenile fish (23.58 ± 3.49 g) were divided into eight groups – four groups were fed every day to apparent satiation, while the other four were fasted for 7 days every 2 weeks. In each feeding regime, two replicates were fed an l ‐carnitine non‐supplemented diet (46 mg kg^?1) and the other two groups were fed an l ‐carnitine supplemented diet (630 mg kg^?1). Fish fed 630 mg l ‐carnitine accumulated two times more l ‐carnitine in muscle than fish fed 46 mg l ‐carnitine. Cyclic fasting reduced the growth performance and lipid content in the liver. Carnitine supplementation did not affect performance and body composition, but decreased the n‐6 PUFA content. Moreover, the combined effects of fasting and carnitine supplementation were observed on reducing the n‐3 fatty acid content. Areas of steatosis were found in the livers of red porgy, but the results revealed that supplementation of l ‐carnitine in cyclic fasted fish contributed towards a lower degree of vacuolization than in fish fed to apparent satiation. Regardless of the feeding regime applied, the spleen of fish fed the l ‐carnitine‐supplemented diet was haemorrhagic and hyper activation of melanomacrophage cells was observed.     

Pigmentation,carotenoids, lipid peroxides and lipid composition of red porgy (Pagrus pagrus) skin reared under open‐cage conditions

Pigmentation capability of red porgy (Pagrus pagrus) skin reared under open sea‐cage conditions and fed an astaxanthin‐enriched diet was studied. Skin lipid peroxide levels and lipid composition were also evaluated to establish the antioxidant role of astaxanthin under these sunlight‐exposure conditions. Fish placed either in an offshore sea cage system (SC) or in an inland tank facility (T) housed inside a ‘shade‐house’ enclosure were fed a commercial diet supplemented with 22 mg kg^?1 astaxanthin. No differences in growth or survival were found. Both groups displayed a red skin, but SC fish presented a darker pigmentation, which externally reflected the higher deposition of melanin, astaxanthin and tunaxanthin found in its skin. The lower level of lipid peroxides found in SC fish might be related with the higher level of astaxanthin mentioned above. Nevertheless, lipid and fatty acid profiles did not show significant differences between groups. Our results indicate that sustainable production of red porgy with a natural red hue is possible on the basis of proper adjustment of two factors illumination and dietary astaxanthin.     

Effects of dietary protein and lipid levels on growth, feed conversion and body composition in rohu, Labeo rohita (Hamilton), fingerlings

Twelve experimental diets (D‐1 to D‐12) in a 4 × 3 factorial design (four protein levels: 250, 350, 400 and 450 g kg^?1 and three lipid levels: 50, 100 and 150 g kg^?1) were formulated. Carbohydrate level was constant at 250 g kg^?1. Rohu fingerlings (average wt. 4.3 ± 0.02 g) were fed the experimental diets for 60 days in three replicates at 2% BW  day^?1. Weight gain (%), specific growth rate (% day^?1) and feed gain ratio (FGR) indicated that diets containing 450 g kg^?1 protein and 100 or 150 g kg^?1 lipid (diets D‐11 and D‐12) resulted in best performance, although results were not significantly different from those of diet D‐9 (400 g kg^?1 protein and 150 g kg^?1 lipid). Protein efficiency ratio was highest with diets D‐6 (350 g kg^?1 protein and 150 g kg^?1 lipid) and D‐9 (400 g kg^?1 protein and 150 g kg^?1 lipid) (P > 0.05) and declined with higher and lower protein diets at all levels of lipid tested. Elevated lipid level (50, 100 or 150 g kg^?1) did not produce better FGR in diets containing 400 and 450 g kg^?1 dietary protein (P > 0.05). The combined effects of protein and lipid were evident up to 400 g kg^?1 protein. Growth and FGR showed consistent improvement with increased lipid levels from 50 to 150 g kg^?1 at each protein level tested except with diets containing 450 g kg^?1 protein. Apparent nutrient digestibility (for protein, lipid and energy) did not show significant variation among different dietary groups (P > 0.05). Whole body protein and lipid contents increased significantly (P > 0.05) with dietary protein level. The results of this study indicate that rohu fingerlings are adapted to utilize high protein in diets with varying efficiency. The fish could utilize lipid to spare protein but there is no significant advantage from this beyond the dietary protein level of 350–400 g kg^?1 in terms of growth and body composition.     

Growth,feed utilization and body composition of Asian catfish (Pangasius hypophthalmus) fed at different dietary protein and lipid levels

This study examined the effect of dietary protein and lipid levels on growth, feed utilization and body composition of Asian catfish Pangasius hypophthalmus reared in cages. Eight test diets were formulated at four protein (340, 380, 420 and 460 g kg⁻¹ crude protein) and two lipid (50 and 90 g kg⁻¹ crude lipid) levels. Fish (initial weight 4.7 g fish⁻¹) were fed the test diets for 8 weeks. Final body weight, weight gain (WG), feed intake (FI), feed conversion ratio (FCR), contents of crude protein, lipid and energy in whole body were dependent on both dietary protein and lipid levels, while specific growth rate (SGR), hepatosomatic index and body moisture content were dependent on dietary lipid level. The WG and SGR increased with the increase in either dietary protein level (at the same lipid level) or lipid level (at the same protein level). The FI and FCR decreased with the increase in dietary protein level (at the same lipid level) or lipid level (at the same protein level). Protein sparing action occurred in case dietary lipid level increased. Fish fed the diet containing 453 g kg⁻¹ crude protein and 86 g kg⁻¹ lipid had the highest WG and SGR, but the lowest FI and FCR, among the diet treatments. There were no significant differences in the protein retention efficiency (PRE) and energy retention efficiency (ERE) among the diet treatments, although PRE and ERE were relatively high in fish fed the diet containing 453 g kg⁻¹ crude protein and 86 g kg⁻¹ lipid. At the end of the feeding trial, body protein content increased, while body lipid content decreased, with the increase in dietary protein content at the same lipid level. Our results suggest that dietary levels of 450 g kg⁻¹ crude protein and 90 g kg⁻¹ lipid are adequate to support fast growth of P. hypophthalmus reared in cages.     

Effect of dietary protein and lipid levels and protein to energy ratios on growth, survival and body composition of the mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775)

The approximate levels of dietary protein and energy that would sustain good growth and survival of the mangrove red snapper Lutjanus argentimaculatus (Forsskal) were determined in two feeding experiments. In the preliminary experiment, six fish meal‐based diets were formulated to contain three protein levels (35%, 42.5% and 50%) and two lipid levels (6% and 12%) for each protein, with dietary energy ranging from 14.6 MJ kg^?1 to 20.5 MJ kg^?1. The protein to energy (P/E) ratios of diets ranged from 20.6 mg protein kJ^?1 to 27.5 mg protein kJ^?1. Diets were fed for 100 days to triplicate groups of snappers with an average initial weight of 24.8 ± 0.4 g. No significant interaction between different levels of protein and lipid was observed. Survival rates (93.8% to 100%), feed conversion ratios (FCR) (2.61–3.06) and condition factors (K) were not affected by different dietary treatments. Regardless of lipid level, fish fed 50% protein diets had a significantly higher specific growth rate (SGR) than fish fed the 35% protein diets, but not compared with the 42.5% diets (P < 0.05). Increasing lipid to 12% in all protein levels resulted in no improvement in growth over the 6% level. Fish body moisture did not vary while lipid levels based on dry matter were high (27.9% to 33.7%). Snapper appear to require more than 40% dietary protein and a high dietary energy level for good growth. In the second experiment, fish (21.1 ± 0.1 g) in four replicate groups were fed for 94 days with three diets (39%, 44% and 49% protein with P/E ratios of 21.1, 23.3 and 25.5 mg protein kJ^?1 respectively) containing similar dietary energy levels of about 19 MJ kg^?1. Average final weight, SGR and FCR were significantly higher in diets containing 44% and 49% protein diets (P > 0.05). There were no differences in survival rates, protein efficiency ratio (PER) and nutrient composition of snapper flesh. All fish had fatty livers. Results indicated that the diet containing 44% protein with a P/E ratio of 23.3 mg protein kJ^?1 was optimum for snapper growth under the experimental conditions used in the study.     

Effect of dietary lipid level on growth, feed utilization and body composition by juvenile grass carp (Ctenopharyngodon idella)

A study was undertaken to determine the effect of dietary lipid level on growth, feed efficiency and body chemical composition of juvenile grass carp. Seven isonitrogenous diets (400 g kg^?1 crude protein) containing seven dietary lipid level (0, 20, 40, 60, 80, 100 and 120 g kg^?1 dry matter) were fed to triplicate groups of 40 fish with initial weight 6.52 g, for 70 days. No obvious and assured essential fatty acid deficiency symptom appeared in fish fed the lipid‐free diet. Excess dietary lipid level (100 and 120 g kg^?1) resulted in decreased feed intake. The best growth performance and feed utilization was observed in fish fed 20–40 g kg^?1 dietary lipid. The fish fed a lipid‐free diet had the lowest protein efficiency and protein retention. Growth performance and feed utilization increased with the increasing dietary lipid levels up to 40 g kg^?1 dietary lipid. Higher dietary level (above 40 g kg^?1) made growth performance and feed utilization decrease and no protein sparing effect was observed. Lipid retention decreased as dietary lipid level increased. Mesenteric fat index (MFI) increased, hepatosomatic index (HSI) decreased with dietary lipid level. The increased MFI and simultaneous decrease lipid retention can be explained by differences in growth. The effect of dietary lipid levels on the chemical composition of tissues was significant only for whole body and muscle. The excess lipid content of liver in all groups was regarded as a slight symptom of fatty liver, which was partly identified by microscopic structural study and lower plasma lipid indexes, comparing to the initial plasma data. In conclusion, grass carp is a fish with low energy requirement and excess dietary lipid level should be avoided.     

The effects of dietary protein and lipid on growth and body composition of juvenile and sub-adult red snapper, Lutjanus campechanus (Poey, 1860)

To allow for the initial identification of practical diet formulations for red snapper culture, the present study was conducted to evaluate the effects of feeding varying levels of dietary protein and lipid on growth and body composition of juvenile and sub‐adult red snapper. Twelve diets were formulated to contain varying levels of dietary protein and lipid. In trial 1, juvenile red snapper (initial mean weight 5.9 g) were offered diets with graded levels of dietary protein (32%, 36%, 40%, 44%) and practical energy to protein ratios. In trial 2, juvenile red snapper (initial mean weight 8.64 g) were offered isonitrogenous diets (44% protein) containing graded levels of dietary lipid (8%, 10%, 12%, 14%). Sub‐adult fish (initial mean weight 151.5 g) were used in trial 3 and maintained on diets similar to those of trial 1 (32–44% protein). Sub‐adult fish (initial mean weight 178.3 g) in trial 4 were offered isonitrogenous diets containing 32% dietary protein and graded levels of dietary lipid (6%, 8%, 10%, 12%). There were no significant differences in growth, feed efficiency ratio (FER) or survival in juvenile fish. Juvenile fish offered 32% dietary protein exhibited a significantly greater (P=0.0497) protein conversion efficiency (PCE) than fish offered a diet containing 44% dietary protein. Juvenile fish in trial 2 also had significantly higher (P=0.005) intraperitoneal fat ratios (IPFRs) at 14% dietary lipid than fish offered diets containing 8–10% dietary lipid, and displayed trends towards greater protein as a percent of whole‐body composition at 8–10% dietary lipid. Sub‐adult snapper in trials 3 and 4 showed no significant differences in growth, FER or survival. However, in trial 4 there was a general trend towards increased % weight gain (P=0.0615), FER (P=0.0601) and final mean weight (P=0.0596) with increasing levels of dietary lipid. Fish in trial 4 offered 6% dietary lipid also had significantly lower (P=0.0439) IPFR and PCE (P=0.0188) than fish offered 12% dietary lipid. Based on data obtained from these trials, inclusion of dietary protein at levels of 32–36% appears sufficient to support growth. For this level of protein, dietary lipid should be ～10% in order to meet the energetic demands of the fish and to spare dietary protein for growth.     

Effect of dietary protein, lipid and carbohydrate ratio on growth, feed efficiency and body composition of pikeperch Sander lucioperca fingerlings

Pikeperch Sander lucioperca fingerlings were fed nine practical diets containing three levels of protein (P=34%, 43% and 50%), lipid (L=10%, 16% and 22%) and carbohydrate (C=10%, 15% and 20%) for 10 weeks in a recirculating water system at 23°C. Dietary treatments were distributed by orthogonal design with dietary energy content ranging from 15.5 to 23.1 MJ kg^?1 diet. Significant differences (P<0.05) in weight gain (%) and feed efficiency (FE) were observed after feeding trial. Relatively low growth and FE were found in fish fed diets containing 34% dietary protein level compared with that of fish fed diets with 43–50% protein levels, suggesting that 34% dietary protein probably is below the protein requirements of pikeperch fingerlings. Fish fed diets containing P43L10C15, P43L22C20 and P50L16C20 had significantly (P<0.05) higher weight gain and FE than fish fed the diets containing other dietary P/L/C ratios. There was no significant difference in weight gain and FE between fish fed diets of P43L10C15, P43L22C20 and P50L16C20. These results may indicate that pikeperch require at least 43% of dietary protein for adequate growth and FE, and considering the fish growth and feed ingredient cost P43L10C15 diet is more cost‐effective formulation for pikeperch fingerling. However, protein efficiency was not significantly affected by dietary P/L/C ratio.     

Effect of dietary protein levels on growth,feed utilization and carcass composition of endangered bagrid catfish Horabagrus brachysoma (Gunther 1864) fingerlings

An 84‐day feeding trial was conducted to study the effect of different levels of dietary protein, 250 (P25), 300 (P30), 350 (P35), 400 (P40) and 450 g (P45) kg^?1 dry matter (DM) on growth, feed intake, feed utilization and carcass composition of bagrid catfish Horabagrus brachysoma fingerlings. Triplicate groups of fingerlings with mean initial body weight of 2.2 g were fed the experimental diets twice daily, till satiation, in 150‐L tanks supplied with flow‐through freshwater. Daily dry matter intake by the fingerlings decreased significantly (P < 0.05) when fed P25 diet, containing 250 g protein kg^?1. The highest body weight gain, specific growth rate (SGR) and protein efficiency ratio (PER), and the lowest feed conversion ratio (FCR) were observed in fish fed 350 g protein kg^?1 diet. The fish fed with P45 diet had the lowest (P < 0.05) carcass lipid content. The polynomial regression analysis indicates that H. brachysoma fingerlings require 391 g dietary crude protein kg^?1 diet.     

Effect of dietary protein on growth, feed conversion, body composition and survival of pike perch fingerlings (Sander lucioperca)

Triplicate groups of pike perch (Sander lucioperca) juveniles were fed six experimental diets containing protein levels varying from 263 to 619 g kg⁻¹ dry matter (d.m.) for 56 days. Dietary protein was supplied by graded amounts of fish meal (with 720 g kg⁻¹ crude protein). Crude lipid and gross energy content of 101–107 g kg⁻¹ and 19.9–20.6 MJ kg⁻¹ remained constant between experimental diets. Pike perch with an initial body weight of 1.05 ± 0.05 g were randomly distributed in 18 tanks of two similar recirculation systems and fed on gradually decreasing feeding rates of 10 to 6% of their body weight per day. Growth performance and feed conversion increased with dietary protein level from 263 to 549 g kg⁻¹ d.m. but did not decline at highest dietary protein level. Protein efficiency ratio declined linearly with increasing dietary protein. Survival ranged between 89.7 and 93.9% and was not affected by dietary composition. Dry matter and crude lipid content of pike perch fingerlings decreased with increasing dietary protein supply and significantly the lowest dry matter and crude lipid levels were observed in fish fed diets containing 619 g kg⁻¹ of crude protein. The dietary protein requirement for pike perch fingerlings calculated by broken‐line and second‐order polynomial regression ranged between 529 and 577 g kg⁻¹, respectively.     

Growth,feed utilization and body composition of African bonytongue,Heterotis niloticus,fingerlings fed diets containing various protein and lipid levels

In order to evaluate the effects of dietary protein and lipid levels on the growth, feed utilization and body composition of Heterotis niloticus fingerlings, a factorial experiment with three replicates was conducted. Six experimental diets containing three crude protein levels (28%, 32% and 36%) and two crude lipid levels (6% and 13%) were tested. Heterotis niloticus (2.34 g) were fed with the diets to apparent satiation, twice a day. For 56 days, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein retention (PR) were significantly affected by dietary protein and dietary lipid levels respectively (P<0.01). The highest WG, SGR and FE were observed for fingerlings fed the diet containing 36% protein and 6% lipid, but no significance difference was found between groups fed with the following diets: P28L13 (28% protein and 13% lipid), P32L6, P32L13 and P36L13. A significant interaction between dietary protein and lipid was observed for WG, SGR, FE and PR. The whole‐body protein, lipid, moisture and ash content were not significantly affected by dietary lipid levels, but body protein and lipid content were significantly affected by dietary protein. The dietary protein‐sparing effect was clearly demonstrated when the dietary energy of lipid increased from 17 to 19.6 kJ g^?1 at 28% crude protein on H. niloticus.     

Influence of dietary protein levels on growth performance and body composition of African bonytongue fingerlings,Heterotis niloticus (Cuvier, 1829)

Two experiments were conducted to examine the influence of dietary protein levels on growth and carcass proximate composition of Heterotis fingerlings. Four isoenergetic practical diets were formulated to contain dietary protein levels from 250 to 400 g kg^?1 diet. Replicate groups of young Heterotis (initial live weight 3.96 and 26.40 g in experiments 1 and 2 respectively) were handfed twice daily to apparent satiation for a period of 42 and 28 days respectively. Statistical analysis revealed that growth rate was significantly affected by dietary protein level (P < 0.01). The highest weight gain was observed in fingerlings fed with 300 and 350 g protein kg^?1 diet for fish size ranging between 3–15 and 26–62 g respectively. There was no significant difference between groups fed with 300, 350 and 400 g protein kg^?1 diet for Heterotis fingerlings (3–15 g) in the one hand; in the other hand, significant differences were found between fish (26–62 g) fed with 350 g protein kg^?1 diet and those receiving 300 and 400 g protein kg^?1 diet, with no significant difference between each other. The specific growth rate varied from 2.4% to 3.1% day^?1. The whole‐body protein, lipid, moisture and ash contents were not significantly affected by dietary protein levels (P > 0.05). The relationships between percentage weight gain and dietary protein levels suggested very similar dietary protein requirement (about 310 g crude protein kg^?1 diet) for Heterotis ranging from 3 to 62 g. The maximum growth occurred at about 345 g protein kg^?1 diet.     

Dietary protein, growth, nutrient utilization and body composition of juvenile blackspot seabream, Pagellus bogaraveo (Brunnich)

When considering new marine species for Mediterranean aquaculture, blackspot seabream emerges as a potential candidate. However, there are scarce data on the nutritional requirements and optimal growth conditions of this species. A 12‐week feeding trial was conducted to evaluate the effects of dietary protein on growth, nutrient utilization and body composition of blackspot seabream (23 g). Five isolipidic diets (12%) with graded levels of protein (20–60%) were distributed, twice a day, to duplicate groups of fish, until satiation. Growth increased significantly with increasing dietary protein up to 40%, but higher protein levels induced a similar daily growth index (1.4). Feed conversion ratio (FCR) decreased with increasing levels of dietary protein (4.2–1.6). No significant differences were detected in protein of whole body blackspot seabream among treatments, but fat percentage decreased with increasing dietary protein. Dry matter and energy digestibility showed a concomitant increase with the reduction in dietary wheat meal, attaining maximal values with high protein diets. These results suggested that the most favourable values for growth and FCR are obtained with diets containing 40% protein. However, the excessive lipid deposition reveals that more nutritional studies are necessary before the species can be established in aquaculture.