Dietary fatty acids have been shown to exert a clear effect on the stress response, modulating the release of cortisol. The role of fatty acids on the expression of steroidogenic genes has been described in mammals, but little is known in fish. The effect of different fatty acids on the release of cortisol and expression of stress-related genes of European sea bass (Dicentrarchus labrax) head kidney, induced by a pulse of adenocorticotrophin hormone (ACTH), was studied. Tissue was maintained in superfusion with 60 min of incubation with EPA, DHA, arachidonic acid (ARA), linoleic acid or α-linolenic acid (ALA) during 490 min. Cortisol was measured by RIA. The quantification of stress-related genes transcripts was conducted by One-Step TaqMan real-time RT-PCR. There was an effect of the type of fatty acid on the ACTH-induced release of cortisol, values from ALA treatment being elevated within all of the experimental period. The expression of some steroidogenic genes, such as the steroidogenic acute regulatory protein (StAR) and c-fos, were affected by fatty acids, ALA increasing the expression of StAR after 1 h of ACTH stimulation whereas DHA, ARA and ALA increased the expression of c-fos after 20 min. ARA increased expression of the 11β-hydroxylase gene. Expression of heat shock protein 70 (HSP70) was increased in all the experimental treatments except for ARA. Results corroborate previous studies of the effect of different fatty acids on the release of cortisol in marine fish and demonstrate that those effects are mediated by alteration of the expression of steroidogenic genes.

The effect of dietary water content on Dicentrarchus labrax growthparameters and resistance to Vibrio anguillarum infection wasinvestigated using commercial pellets with identical energy contents and differentmoisture levels. The first experiment hypothesis was that moisturizing pelleted ration canhave an impact on Dicentrarchus labrax growth performance by theosmoregulation energy cost reduction. In a second time, the experiment explores the effectof water addition in pellets on the fish resistance to a disease. A specific device wasbuilt to uniformly moisturize dry pellets to different moisture levels, i.e. 8%, 20%, 40%and 60%. After an acclimation period and a 54-day rearing period, the control fish hadgrown from 72.7 ± 17.9 g to133.3 ± 29.4 g. Nosignificant differences were recorded for fish growth parameters. After the growth period,the tagged fish were mixed and challenged by bath exposure to live Vibrioanguillarum in triplicate. After 7 days, mortality was significantly lower inthe group of fish fed with pellets containing 60% water. Adding water toDicentrarchus labrax feed did not affect fish growth parameters butincrease its resistance to a Vibrio anguillarum infection. The moisturizing processcould be used to add specific compounds (such as probiotics or vitamins) to pellets justbefore fish feeding and could have a positive effect on fish rearing.

Replacing aquaculture feeds based on fisheries-derived resources with plant-based dietscould be a relevant strategy to improve the sustainability of aquaculture. Recent studieson sea bass have shown that the total and early replacement of marine products by plantproducts would have a moderate effect on fish growth and body lipid content. Whether aplant-based diet impacts behavioural and physiological traits possibly linked to fishwelfare, is not known, however. Here, we studied the effect of a totally plant-based dietintroduced at an early stage of sea bass development on self-feeding behaviour, learningability in a T-maze and stress biomarkers. We first compared learning processes inself-feeding conditions, between naive fish fed a plant-based diet (PBF) and fish fed aclassic marine diet (MF). Then, we tested fish individually in a T-maze to compare the twofeed groups for swimming activity, exploration and the ability to learn to discriminatebetween two two-dimensional objects associated with a reward. Blood physiologicalvariables, including stress indicators (cortisol and glucose concentrations), were alsodetermined. We did not find any indications of differences in self-feeding behaviourbetween PBF and MF in the first 30 days. A second experiment showed similar swimmingactivities in both fish categories. The “no-choice” percentage was high in both fishcategories (~60%), but all the fish moved preferentially toward the reward. Theirfirst turns indicated an ability to discriminate between two two-dimensional objects tocomplete a simple task. However, the high percentage of “no-choice” responses in both fishcategories could have rendered the results non significant. The T-maze test procedureinduced the production of high concentrations of cortisol, indicating acute stress in fishof both groups during testing. Plasma cortisol concentration was higher in MF than PBF,suggesting that the plant-based diet may affect the short-term release of cortisol. Thisstudy provides the first insight into the impact of a plant-based diet on sea bassbehavioural traits, and confirms the effect of this diet on cortisol release in responseto stress. Overall, in this first experiment, we did not find any major impact of aplant-based diet on sea bass behavioural traits, which is an interesting point for thedevelopment potential of such a sustainable aquaculture strategy.

Inter- and intraspecific crossbreeding experiments were conducted to evaluate the aquaculture potential of hybrids in the genus Dicentrarchus, focusing on fertilisation and hatching success. The experimental design consisted of 24 controlled crosses in which individual and pooled fertilisations were made between wild D. labrax individuals (8 dams and 5 sires originating from West Mediterranean and Atlantic populations) and wild D. punctatus (6 sires). Three experiments were successively performed: (1) dams from the Mediterranean population, individually considered to have good egg quality, (2) dams from Mediterranean population, individually considered to have poor egg quality and (3) crossbreeding using pooled eggs from the Atlantic population. In each case, batches of these eggs were fertilized by sperm from males of the two species. Sperm cell quality (concentration and motility) was verified before experimentation in all cases and equal numbers of sperm cells from each male were used to individually (without inter-sire competition) fertilise egg batches. Through the repeated artificial crosses between female common sea bass Dicentrarchus labrax (Linnaeus 1758) and male spotted sea bass D. punctatus (Block 1792), these experiments showed that no post-zygotic reproductive barriers exist to interspecific hybridisation between these two species when using D. labrax as dams and D. punctatus as sires. Phenotypically, the F1 hybrids were easily recognisable: they inherited the characteristic black spots of D. punctatus. Furthermore, embryo survival was significantly higher in interspecific crosses compared with intraspecific controls, showing increased fitness for this trait (increased performance at early life stage). Then, the experimental breeding design validates the observation that West Mediterranean and Atlantic common sea bass populations are different. Indeed, the inter-population crosses (between West Mediterranean dams and Atlantic sires) also revealed increased fitness at early life stages in comparison with the progeny of intra-Atlantic population crosses. However, these individuals were still smaller than their interspecific counterparts. The ability to produce viable F1 hybrids will have significant implications for the practical improvement of sea bass aquaculture.

Sex ratios in farmed European sea bass are highly biased towards males (75 to 95%), which is problematic for aquaculture. In this mini-review, we re-analyse fisheries literature data about sex ratios in wild sea bass from 13 population samples, representing altogether 4889 individuals covering the major part of the distribution range of the species. We find that as a whole, the sex ratio of wild populations is biased towards females (59.4% females, p < 0.001), but that the sex ratio of the younger fish (<30 cm total length) is balanced (52.0% females, p = 0.15), while the sex ratio of the older fish is heavily biased towards females (69.5% females, p < 0.01). Possible causes of these differences (differential longevity, biased sampling) are discussed. When age-group sex ratios are available (three population samples out of 13), significant variation between age groups appears, part of which is most likely of environmental origin. This study shows that the excess of males in culture is not a characteristic of the species, but rather a consequence of the environments used in culture, interacting with a complex system where both environmental and genetic influences govern sex determination in sea bass.

A method of geometric morphometrics was used to characterize body shape variation inmeiotic gynogenetic and triploid sea bass in comparison with diploid controls. A total of13 coordinate landmark data were recorded on the profile of 34-month-old control(n = 81), gynogenetic (n = 117) and triploid(n = 131) siblings generated from two females (A and B). Three mainaxes of morphometric variation were consistent, and these accounted for 60.8 and 57.6% ofthe total variability in females A and B, respectively. There were significant shapedeviations of triploid and gynogenetic fish relative to the controls, and differences wereparticularly evident in the progeny of one female. Overall, triploids displayed a moreslender shape than diploids, whereas gynogenetic fish were deeper bodied and had flexedcaudal peduncles and cranial features. The results are discussed especially in relation tothe characterization of triploid fish for commercial purposes.

The long term influence of individual biological rhythms on group feed demand behaviour was investigated in European sea bass (Dicentrarchus labrax) held under controlled environmental conditions with an on-demand feeding system. The experiment was realized over 219 days with 190 fish distributed on 4 tanks. Sea bass had a mean body mass comprised between 139 g to 183 g. The number of feed demand acts by each individual was calculated daily, and the population could thus be partitioned into three categories (high-, low- and zero-triggering fish). The duration of the period that an individual held high-triggering status could vary, but was 63 ± 16 days on average. The transition period between two highest-triggering fish in one tank was on average 4 ± 4 days. The group feeding rhythm followed the same pattern of feed demand rhythm as the highest-triggering individual fish. When the highest-triggering fish was nocturnal, the totality of feed demand in the group was realized during the night with one peak at 22:00, corresponding to dusk under experimental conditions. When the highest-triggering fish was diurnal, the majority of feed demand in the group was realized during the light period with one peak at 06:00, corresponding to dawn, and/or another at 12:00. This study therefore highlights that sea bass group feeding behaviour is not the sum of individual feed demand behaviours, but is directed by the rhythm and behaviour of a few high-triggering fish. The regular changes of high-triggering fish in the group proved that it was not the identity of these particular fish that was most important for the group, but their role as a feed demand leader.

Genetic parameters for carcass quality traits were estimated in 27 families of sea bass (3 dams × 9 sires factorial mating design), raised mixed in the same tanks starting before hatching. Offspring parentage was determined a posteriori using 6 microsatellite loci. Carcass quality traits were recorded at 818 days post fertilization (mean standard length: 32.6 ± 3.1 cm). Genetic parameters were estimated from the sire half sib variance and covariance components. Heritability of body weight (BW) and carcass processing traits (standardized to body weight) percent head weight (Head%), percent viscera weight (Viscera%) and percent visceral fat weight (VisceFat%) were relatively high ranging from 0.48 ± 0.15 (Viscera%) to (Head%); the estimate of heritability for fillet yield (Fillet%) was lower (0.25 ± 0.10) but was significantly greater than zero. Body weight was positively correlated to Fillet%, Viscera%, and VisceFat%, and negatively correlated to Head%. These results indicate that these carcass processing traits can be modified by directional selection and that selection for greater BW would lead to an increase of Fillet%, Viscera% and VisceFat% and a decrease of Head%.

Muscle lipid content (MuscleLipid%) was determined using two indirect methods: measurements with a Torry Fish Fatmeter® (TorryLipid) and determination of the percentage of dry matter content (MuscleDry%) via desiccation. Both measures were highly correlated to chemical measurements of MuscleLipid%. Regression analysis indicated a superior predictive value of TorryLipid suggesting that MuscleLipid% may be evaluated via rapid, non lethal measurements with a Torry Fish Fatmeter. Heritability estimates of TorryLipid and MuscleDry% differed significantly from zero (TorryLipid: 0.28 ± 0.12, MuscleDry%: 0.36 ± 0.14) indicating that MuscleLipid% could be lowered by directional selection. TorryLipid and MuscleDry% were weakly correlated to body weight and carcass processing traits suggesting that simultaneous improvement of MuscleLipid% and other carcass quality traits may require definition of multi-trait selection indices.

Four replicated groups of sea bass (Dicentrarchus labrax) larvae were fed diets containing an extra-high level of highly unsaturated fatty acids (HUFA) (XH; 3·7 % EPA+DHA), a high level of HUFA (HH; 1·7 %), a low level of HUFA (LH; 0·7 %) or an extra-low level of HUFA (XLH; 0·5 %) from day 6 to day 45 (experiment 1; XH1, HH1, LH1, XLH1). After a subsequent 1-month period feeding a commercial diet (2·7 % EPA+DHA), the capacity of the four initial groups to adapt to an n-3 HUFA-restricted diet (0·3 % EPA+DHA; R-groups: XH2R, HH2R, LH2R, XLH2R) was tested for 35 d. Larval dietary treatments had no effect on larval and juvenile survival rates. The wet weight of day 45 larvae was higher in XH1 and HH1 (P < 0·001), but the R-juvenile mass gains were similar in all treatments. Δ-6-desaturase (Δ6D) mRNA level was higher in LH1 and XLH1 at day 45 (P < 0·001), and higher in LH2R and XLH2R, with a significant increase at day 118.Concomitantly, PPARα and PPARβ mRNA levels were higher in XLH1 at day 45, and PPARβ and γ mRNA levels were higher in XLH2R at day 118, suggesting possible involvement of PPAR in stimulation of Δ6D expression, when drastic dietary larval conditioning occurred. The low DHA content in the polar lipids (PL) of LH1 and XLH1 revealed an n-3-HUFA deficiency in these groups. Larval conditioning did not affect DHA content in the PL of R-juveniles. The present study showed (i) a persistent Δ6D mRNA enhancement in juveniles pre-conditioned with an n-3 HUFA-deficient larval diet, over the 1-month intermediate period, and (ii) brought new findings suggesting the involvement of PPAR in the Δ6D mRNA level stimulation. However, such nutritional conditioning had no significant effect on juvenile growth and lipid composition.

Mass budget of the sea bass (Dicentrarchus labrax) farming losses was examined. Experiments were carried out in April, September and November 2001 in tanks of 8.5 m3 containing sea bass of 1, 31 and 53 g, respectively. Samples were taken at the input and discharge points of the tank at hourly intervals over 24 h. They were later analysed for nutrient concentration, as well as particulate organic carbon and nitrogen, chlorophyll a (Chl a) and total bacterial abundance. Despite the high water supply (exchange rate: 50% h−1), NH4 concentration was significantly higher in discharge water than in input water in all three experiments independent of fish size. The same was found to hold true for PO4 for part of the day (April, November) or for the entire day (September). NO3 and SiO2 ions did not show any differences during April. Particulate organic carbon (POC) and nitrogen (PON) were higher in the discharge water in all seasons. Chl a concentration was higher in the discharge water during the entire day in September whereas bacteria presented higher counts in the output water only during part of the day in April. It was found that 5−7% of the nitrogen supplied is released into the water column as fine particulate material in the form of PON and 21−29% as NH4. A small proportion (13−16%) of supplied phosphorus (P) was released as PO4. The results provided in the present paper are useful in assessing environmental changes in water quality in the vicinity of fish farms in the Mediterranean.

Une analyse phylogéographique de quinze échantillons de Dicentrarchus labrax dont cinq sont originaires de Méditerranée occidentale, sept de Méditerranée orientale et trois échantillons d'élevage en provenance de trois piscicultures françaises a été effectuée à partir du polymorphisme de six locus microsatellites. Parmi les échantillons orientaux, trois ne se regroupent pas en fonction de leur origine géographique, mais plutôt avec le groupe occidental. Ces échantillons présentent également une diversité allélique légèrement réduite, indiquant qu'ils proviennent d'un nombre limité de géniteurs d'origine occidentale. Parmi les stocks d'élevage, un seul montre une réduction significative de la variabilité génétique, ce qui indique que ces cheptels sont ouverts et font largement appel à des géniteurs sauvages. L'utilisation d'alevins d'origine occidentale pour ensemencer les premières fermes d'élevage du bassin oriental remonte au plus tard au début des années 80. Ceci soulève la question des mécanismes biologiques expliquant le maintien de poissons d'origine occidentale dans un contexte oriental pendant au moins deux ou trois générations.

The aim of the study was to determine the influence of dietary phospholipid concentration on survival and development in sea bass (Dicentrarchus labrax) larvae. Larvae were fed from day 9 to day 40 post-hatch with an isoproteic and isolipidic formulated diet with graded phospholipid levels from 27 to 116 g/kg DM and different phospholipid:neutral lipid values. The best growth (32 mg at the end of the experiment) survival (73 %) and larval quality (only 2% of malformed larvae) were obtained in the larvae fed the diet containing 116 g phospholipid/kg DM (P < 0·05). These results were related to the amount of phosphatidylcholine and phosphatidylinositol included in this diet (35 and 16 g/kg respectively). Amylase, alkaline phosphatase and aminopeptidase N activities revealed a proper maturation of the digestive tract in the two groups fed the highest phospholipid levels. Regulation of lipase and phospholipase A2 by the relative amount of their substrate in the diet occurred mainly at the transcriptional level. The response of pancreatic lipase to dietary neutral lipid was not linear. As in mammals 200 g triacylglycerol/kg diet seems to represent a threshold level above which the response of pancreatic lipase is maximal. The response of phospholipase A2 to dietary phospholipid content was gradual and showed a great modulation range in expression. Sea bass larvae have more efficient capacity to utilize dietary phospholipid than neutral lipids. For the first time a compound diet sustaining good growth, survival and skeletal development has been formulated and can be used in total replacement of live prey in the feeding sequence of marine fish larvae.

Sexual differentiation was studied at the histological level using a mixture of 30 families of sea bass Dicentrarchus labrax. Most of the fish (93%) differentiated into males as usually observed in farmed populations. All testes were differentiated when the males reached 12 cm and no more undifferentiated fish were found from 419 days post-fertilization (p.f.). In 28% of the males, among the biggest, sexual differentiation had already begun at 168 days p.f. (8.3–9.5 cm) and these fish started spermatogenesis in their first year of life. The other males differentiated later and remained immature at the end of their first year of life. Ovaries could be identified at the histological level from the age of 168 days p.f. (7.9–9.0 cm) and the females became significantly longer than the males from the age of 191 days p.f., i.e. during the process of ovarian differentiation. In the studied group, 62% of the males developed intratesticular oocytes. Such intersexuality had no consequence on growth rate. Intratesticular oocytes were also recorded in testes of wild males originating from Atlantic (Britain and Gulf of Gascogne) and West Mediterranean showing that juvenile intersexuality is not restricted to farmed populations but is a widespread phenomenon in sea bass.

This paper describes the suitability of a closed recirculation system to study the development of fish larvae in a strictly controlled environment, where only feeding was varied (fed, starved, delayed and late fast treatments). The system served both as an incubator and hatchery. The time variation of physical and chemical parameters together with survival and growth of reared sea bass larvae (Dicentrarchus labrax) were studied over the first month of life. The recirculation design allowed for the maintenance of levels of ammonia, nitrite and nitrate below those cited as responsible for mortality or decreased feeding ability in other marine fish larvae. Almost no larval mortality occurred in the fed larvae from day 9 after hatching. The starved group of larvae showed a sharp decline in survival after 16 days of food deprivation. Larvae for which feeding was delayed until day 13 ceased dying 4 days after food was supplied. Fast feeding on days 24 and 25 had no effect on larval survival. Growth in length was similar during the first 2 weeks of larval life regardless of feeding treatment. Two days of late fast had no effect on larval growth. Growth patterns of fed larvae in this study were similar to those reported for larvae reared in flow through systems. We believe that survival and growth of the reared larvae was a direct function of diet, and that the type of rearing system did not adversely affect these parameters. The rearing design and the results obtained suggest that future nutritional studies of field-collected larvae will benefit from this kind of rearing experiment.

The relationship between serum protein, immunoglobulin concentrations and protein molecular weight profile (PMWP) alterations of sea bass (131.3 ± 4.3 g) reared in sea water with sublethal concentrations of ammonia was studied over two periods totalling 116 days. During the exposure period (62 days) the first group (group 1) lived in sea water with 0.204 mg·L−1 unionized ammonia nitrogen equivalent to 12 % of the lethal concentration for 50 % of a population exposed for 96 h to ammonia (96-h LC50), whilst the second group (group 2) lived in sea water with 0.340 mg·L−1 UIA-N equivalent to 20 % of the 96-h LC50 of ammonia. Then, the two groups were left for a recovery period (54 days) in the same water as the control group (group 0). The determination of the total immunoglobulin (Ig) concentration was carried out by enzyme-linked immunosorbant assay (ELISA). Gel filtration columns were used for the serum PMWP. Serum Ig concentration of the exposed fish (group 2: 1.76 ± 0.43 mg·mL−1; group 1: 1.19 ± 0.33 mg·mL−1) was lower than the control group 13.39 ± 1.01 mg·mL−1) after 21 days of exposure period but this difference was reduced at the end of this period (day 62) and treated group Ig concentrations switched to higher than the control group after the recovery period (day 116, group 2: 9.75 ± 1.84 mg·mL−1; group 1: 7.50 ± 1.22 mg·mL−1 group 0: 6.38 ± 1.13 mg·mL−1). In fact, at the end of the experiment, the cumulative Ig production difference between fish exposed to ammonia and the control was less than 10%. Although a similar evolution of the Ig serum occurred with protein concentration, the serum protein concentration deficit of group 1 was restored at the end of the exposure period (group 2: 46.49 ± 2.34 mg·mL-1; group 0: 46.74 ± 1.97 mg·mL−1) and the cumulative production during the experiment was not significantly different between group 1 and group 0. However, this remained lower for group 2. During the exposure period, the PMWP of treated fish moved towards smaller molecular weight proteins. This alteration of the PMWP showed that the 0.2-kDa fraction increased, and another fraction appeared at the end of the exposure period. However, at the end of the recovery period, no difference was found between the PMWPs of control and treated fish. The alterations of the serum protein and Ig of fish reared, for a limited period (2 months), in water with sublethal concentrations of ammonia (20 % 96-h LC50 or less) should disappear completely after a few months in normal rearing conditions.

The common dentex (Dentex dentex) is a sparid fish which is considered a suitable candidate for Mediterranean aquaculture. A seven-weeks feeding trial was conducted over the summer period with common dentex, sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax). All three species were fed to visual satiety with two practical diets with varying crude protein and crude fat levels (55 % protein, 9 % lipids; 46 % protein, 17 % lipids). The initial body weights were 8.2, 11.6 and 17.3 g for common dentex, sea bass and sea bream, respectively. In all cases, specific growth rates were not significantly affected by dietary treatment, but they varied among species (sea bass 1.7-1.8 %; sea bream 2.1-2.3 %; common dentex 3.1-3.2 %). When comparisons between fish species were made, we observed that the increase in growth rates was linked to a decrease of the whole body fat content, as a consequence of a greater utilisation of dietary lipids as energy substrates. Furthermore, in common dentex, the 17 % lipid diet was able to improve protein retention, but this diet effect was less significant in sea bream and sea bass. In contrast to sea bream, the 17 % lipid diet did not up-regulate plasma GH levels in common dentex, which provides additional evidence for a more efficient utilisation of dietary lipids.

A sperm cryopreservation protocol adapted from turbot, was tested on sea bass using either 250-μL straws or 1.5-mL cryovials. A dilution to 1/3 in Mounib's extender and a cooling rate of −65 °C·min−1 allowed frozen sperm to recover an initial motility similar to that of fresh sperm at thawing; however, significant differences in motility (P < 0.001, n = 10 fish semen) were observed at further post-activation times, the motility decrease being faster in thawed sperm. At the experimental scale, triplicate inseminations of 2-mL aliquots (approximately 2 000 eggs) showed a significant fertility decay of thawed sperm compared to that of fresh sperm (P < 0.01, n = 12 fish semen) when a discriminating 35·103 spermatozoa to egg ratio was applied. When 70·103 and 200·103 spermatozoa per egg were provided in the same experimental conditions, no significant difference appeared between the fertilisation rates of fresh and thawed sperm. In order to validate the procedure for production or cryobank purpose, a scaled-up protocol was established. Two and 50 mL batches of eggs (approximately 2·103 and 50·103 eggs, respectively) were inseminated in triplicate using either fresh or thawed individual sperms of 5 males with 200·103 spermatozoa per egg. The mean fertility decreased by 23.5 % due to cryopreservation. This decline was explained by the loss of fertility of only one sperm, and only in large-volume conditions, probably due to the delay of use after thawing.

The incorporation of various bulk agents by substitution of an equivalent amount of the basal mixture was studied in terms of protein digestibility, growth performance and body composition in European seabass (Dicentrarchus labrax) juveniles. During the growth trial, triplicate groups of 40 seabass (mean initial weight: 7.0 g) were grown in seawater (salinity: 35; temperature: 18 °C) over 60 days. Fish were hand-fed, three times a day, one of seven experimental diets. Bulk agents tested at 10 or 20 % level of incorporation were silica, cellulose and a natural zeolite (chabamin). Feeding rates were adjusted in proportion to the percent dilution of the control diet without bulk incorporation. The incorporation of the bulk agents, at a 10 and 20 % level, did not affect protein digestibility or growth performance. Dietary bulk incorporation reduced feed efficiency values, particularly at the 20 % incorporation level. However, this reduction was mostly caused by the dietary nutrient dilution of the bulk-incorporated diets, rather than by a negative effect of the bulk agents as dietary ingredients. In comparison to the control treatment, bulk incorporation at 10 and 20 % level did not affect protein retention values. When compared with the control diet, 20 % bulk agent incorporation changed the evacuation profile of faeces and increased faecal egestion time.

A study on nitrogenous and phosphorous waste production in European seabass (Dicentrarchus labrax) was carried out in a flow-through land-based farm. The main objectives were (i) to calculate nitrogenous (N) and phosphorous (P) waste production (particulate and dissolved) from in situ measurements for different rearing ponds with specific fish biomasses, fish sizes and flow rates, (ii) to establish nitrogenous and phosphorous waste production budgets, ratios and equations, and (iii) to compare, for the whole farm, in situ measurements to estimate N and P waste production from waste equations. Waste production was manifest by an increase in concentrations of total ammonia nitrogen, total Kjeldhal nitrogen, particulate nitrogen, dissolved phosphorus and total phosphorus concentrations in the outlet water compared to the inlet water for both batches and whole farm. However, no production of nitrite or nitrate was observed. In our budgets, the N and P amounts from biomass gains and wastes were explained by the N and P derived from feed over the range 83.9−105.2 % and 66.5−104.6 % respectively, depending on the fish batch. Values were respectively 103.4 and 87.5 % for the same calculations in the farm. When the whole-farm waste production was calculated from previous equations derived from batches, and then compared with the measured data, the percentages of recovery (estimated by the ratio predicted data/measured data) were 88 and 94 % for total-N and total-P respectively.

A trial was carried out to compare the growth performance, body composition and apparent digestibility coefficients (ADC) of diets by seabass, with an initial weight of 13.5 g, fed diets including fish meal (68.6 % of the dietary protein) or soybean meal (65.6 % of the dietary protein) as the main protein sources. Microbial phytase was added to the soybean meal based diet (1 000 and 2 000 IU·kg−1) and to the fish meal based diet (2 000 IU·kg−1) in order to study its effect on phosphorus utilisation. Results of this trial showed that growth rate, feed conversion and nitrogen retention were significantly better in fish fed the fish meal based diet. Energy retention was similar in both groups. ADC of protein were similar among groups. ADC of phosphorus was significantly higher in the fish meal based diet (63 %) than in the soybean meal based diet (25 %). Supplementation of the fish meal based diet with microbial phytase did not improve the ADC of phosphorus, while in the soybean meal based diet the inclusion of 1 000 and 2 000 IU·kg−1 of microbial phytase significantly increased the ADC of phosphorus to 71.5 % and 79.8 %, respectively. It is concluded that for practical purposes supplementation of diets with microbial phytase may prove valuable in diets including high levels of plant feedstuffs.