Feeding ragworm (Nereis virens Sars) to common sole (Solea solea L.) alleviates nutritional anaemia and stimulates growth

Common sole fed with commercial pellets develop anaemia and are restricted in their growth performance. The anaemia can be the result of a difference in feed intake, a nutritional deficiency, an inflammatory response to infection or combinations of these aspects. In this study, it was investigated whether feeding ragworm would alleviate the anaemia and stimulate growth. Sole were fed one of three diets: a commercial feed, a commercial feed treated with ragworm extract or chopped ragworm. By comparing groups, three hypotheses were tested: (1) feeding ragworm alleviates the anaemia and positively affectS the sole's metabolic performance reflected in feed intake, feed efficiency and growth; (2) anaemia is alleviated by a higher feed intake when feeding ragworm and (3) anaemia is caused by an inflammatory response to infection. The sole fed with a commercial diet suffered from anaemia. Feeding sole with ragworm alleviated the anaemia as the average haematocrit level nearly doubled in these fish as compared to fish fed pellets. Investigation of the expression of genes in the liver indicated that the anaemia in sole fed pellets is a nutritional anaemia and not an anaemia due to an inflammatory response. Sole fed ragworm showed improved growth which may be a consequence of the higher haematocrit levels in these fish increasing their oxygen carrying capacity. Addition of ragworm extract to the pellets levelled the feed intake between pellets and ragworm, but did not improve the anaemic state of sole and had only a limited effect on growth.     

Effect of stocking density and protein/fat ratio of the diet on the growth of Dover sole (Solea solea)

Two hundred and fifty soles (30 g initial weight) were randomly stocked in 12 tanks (recirculation system) at two different stocking densities (2.3 and 1.3 kg m^?2) and fed on two different diets (50% and 54% of crude protein and 21% and 18% of total lipid, respectively, for diets A and B) with triplicate tanks for treatment. The trial lasted for 300 days. Fish stocked at low density showed a significantly higher weight gain than the fish reared at 2.3 kg m^?2 density (94.1±7.4 vs. 78.9±8.2 g, P<0.01) with a specific growth rate (SGR) of 0.46±0.11 and 0.43±0.16 (P<0.01) respectively. Feed conversion ratio (FCR) was more favourable for lower density groups (2.50 vs. 2.64, P<0.01). Diet B led to a higher final weight (124.1 vs. 110.2 g, P<0.01) and a better feed utilization (FCR: 2.49 vs. 2.65, P<0.01). Except for the lipid content, which was higher in the low‐density group (2.6% vs. 2.3%, P<0.05), proximate composition of sole's muscle was not influenced by treatments. Dover sole reared at low stocking density showed higher monounsaturated fatty acid (35.27% vs. 34.40%, P<0.01) and lower saturated fatty acid (24.36 vs. 26.13%, P<0.01) contents, and lower atherogenic (0.67 vs. 0.75, P<0.01) and thrombogenic (0.28 vs. 0.32, P<0.01) indexes.     

The effects of starving and feeding on Dover sole (Solea solea,Soleidae, Linnaeus, 1758) stress response and early larval development

In the view of an urgent necessity to improve the quantity and the quality of farmed fish species, there is a strong need to improve our basic knowledge on the effects of first feeding during the developmental stages of fish larvae. High mortality, mainly due to food deprivation or inappropriate food quality, has been observed in many larval fish species, but knowledge about the morphological, biochemical and molecular processes related to this topic is still poorly understood. The understanding of the early larval ontogeny as well as the larval nutritional requirements and the molecular and cellular mechanisms elicited by fish larvae during food deprivation and starvation are thus of primary importance. At this regard, this study investigates, in Dover sole larvae, the effects of starvation and starving/re‐feeding procedures at a morphological, histological, biochemical and molecular level. The results evidenced that starved larvae progressively decrease in growth, lipid content, affected their gastrointestinal tract and muscle development and increased cortisol and heat shock protein 70 levels. On the contrary, starved and re‐fed larvae showed, after the restoration of a favourable feeding condition, a compensatory growth. In conclusion, this is the first study analysing through a multidisciplinary approach the effects of food deprivation on the development of an important economic species, the Dover sole.     

Effects of light intensity on growth,feeding activity and development in common sole (Solea solea L.) larvae in relation to sensory organ ontogeny

The effects of four light intensities (1000 lx, 500 lx, 50 lx, 3 lx) on growth, survival and feeding activity in common sole (Solea solea L.) larvae were studied from 4 to 51 days post hatching (dph). During the pelagic larval stage (4–12 dph), larvae reared at 3 lx showed a lower growth. From 19 onwards, the larvae reared under 3 lx displayed a significant (P ≤ 0.05) higher SGR than the other treatments and a higher final weight compared to 1000 lx and 500 lx. Survival rate was higher under intermediate light intensities (500 and 50 lx). Larvae reared at 3 lx displayed a significant delay in the degree of metamorphosis compared to the other treatments, while at 33 dph metamorphosis was completed under all treatments. Histological examination revealed the importance of vision and light in the first feeding of this species, while after metamorphosis, the full development of other sensory organs indicated that feeding activity is also mediated by chemosensory perception. Results indicate that high light intensity seems to be more suitable during the pelagic larvae, while the opposite would ensure better growth from the onset of metamorphosis to the benthic phase.     

Effect of vitamin B12 and taurine on the alleviation of nutritional anaemia in common sole (Solea solea)

Sole fed commercial pellets develop a nutritional anaemia. This study assessed the impact of dietary B12 and taurine on the haematocrit (Hct) and haemoglobin (Hb) level and mineral absorption in anaemic sole. Anaemic sole was fed one of four diets. Diets were equal regarding mineral, amino acid and macronutrient composition and formulated, according to a two by two factorial design: two B12 (0.34 vs. 1.9 mg kg dm^?1) and two taurine levels (3.5 vs. 7.6 mg kg dm^?1). The feeding level was restricted and equal for all diets. Hct and Hb levels in anaemic sole are influenced by dietary B12. A “high” level of B12 increases the Hct and Hb level. An increasing level of taurine suppresses the stimulating effect of the “high” level of B12. The applied B12 and taurine levels were unable to completely alleviate the anaemia in sole. Nevertheless, sole needs high dietary levels of B12 to alleviate anaemia. The impact of B12 and taurine on Hb and Hct was not related to a change in the absorption of iron. A “high” level of B12 positively affected the absorption of chromium and a high level of taurine negatively affected the absorption of cobalt in sole.     

Patterns in the spawning of cod (Gadus morhua L.), sole (Solea solea L.) and plaice (Pleuronectes platessa L.) in the Irish Sea as determined by generalized additive modelling

Eleven ichthyoplankton cruises were undertaken covering most of the Irish Sea during the period February to June, 1995. To identify spawning localities and investigate temporal trends in egg production, the data on stage 1 A egg distributions of cod ( Gadus morhua ), plaice ( Pleuronectes platessa ) and sole ( Solea solea ) have been modelled using generalized additive models (GAMs). A two-stage approach was adopted where presence/absence was firstly modelled as a binary process and a GAM surface subsequently fitted to egg production (conditional on presence). We demonstrate that this approach can be used to model egg production both in space and in time. The spawning sites for cod, plaice and sole in the Irish Sea were defined in terms of the probability of egg occurrence. For cod, we demonstrate that by integrating under predicted egg production surfaces, a cumulative production curve can be generated and used to define percentiles of production and thus delimit the extent of the spawning season. However, for plaice and sole, the surveys did not fully cover the spawning season and the limitations that this imposes on GAM modelling of these data are discussed. Comparison of the spawning sites in 1995 with historical data suggests that the locations of cod, plaice and sole egg production in the Irish Sea have probably remained relatively constant over the last 30 years.     

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.     

Growth,feed utilization and liver histology of juvenile common sole (Solea solea L.) fed isoenergetic diets with increasing protein levels

This study was undertaken to determine the influence of dietary protein levels on growth, feed utilization and liver histology in common sole. Four isoenergetic diets were formulated to contain four different crude protein levels: 39 (P39), 45 (P45), 51 (P51) and 57 (P57) % dry weight. Fifty animals per tank (initial weight 10.2 ± 0.4 g) were randomly distributed into twelve 500 litre square tanks (bottom surface: 5600 cm²) connected to a closed recirculation system. The diets were tested in triplicate for 84 days. At the end of the experiment, the final weight ranged from 19.6 (P39) to 25.4 g (P57). The specific growth rate showed statistical differences between groups, with the best results in the group fed diet P57 (1.07% day^?1). Significant differences between groups were also recorded for the feed conversion ratio, with values of 1.31, 1.28, 1.12 and 0.94 in P39, P45, P51 and P57 respectively. Gross lipid efficiency was also significantly affected by the dietary treatment, with the highest value (42.07%) found in P57. Ammonia excretion, expressed as g 100 g^?1 protein intake, was significantly lower for group P39 (2.46) than groups P51 (4.70) and P57 (4.75). Increased incidence of lipid droplets in hepatocytes was observed when the dietary protein levels increased and/or dietary lipid decreased.     

The effect of dietary hydrolysed fish protein concentrate on the survival and growth of juvenile Dover sole, Solea solea (L.), during and after weaning

The growth and survival of 290 mg sole, Solea solea (L.), during and after weaning onto diets containing varying amounts of hydrolysed fish protein concentrate (HFPC) were determined. Survival ranged between 75.5% and 42.5% (91% with a control diet containing polychaete and mollusc meals) during the weaning period and was positively correlated with the level of HFPC in the weaning diet. After weaning, when the fish were ～ 940 mg in weight, no significant correlation was found between growth rate and the level of HFPC in the diet over a period of 22 days. Diet digestibility and its importance during weaning is discussed in relation to the digestive physiology of sole. Weaned sole were fed exclusively on a formulated diet in a sand-free tank at an average temperature of 16.5°C for an 18-month period, achieving a final average weight of 133.1 g ± 40.1 SD (217.5 mm ± 19.1 SD).     

The effect of food type (formulated diet vs. natural) and fish size on feed utilization in common sole,Solea solea (L.)

This study compares the effect of food type (formulated diet vs. natural food) and fish size on protein and energy utilization efficiencies for growth in common sole, Solea solea (L.). Replicate groups of common sole (mean initial body weight ± SD was 45.7 g ± 2.1 and 111.2 g ± 4.2) received the diets at five (natural feed) or four (formulated diet) feeding levels. The protein utilization efficiency for growth (k_gCP) was higher (P > 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.40 and 0.31). Likewise, the energy utilization efficiency for growth (k_gGE) was higher (P = 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.57 and 0.33). The protein maintenance requirement was not different between food types (P = 0.64) or fish size (P = 0.41) being on average 0.82 g kg^?0.8 day^?1. The energy maintenance requirement was not different between food type (P = 0.390) but differed between fish size (P = 0.036). The gross energy maintenance requirement of small common sole was 35 kJ g^?0.8 day^?1. The gross energy maintenance requirement of large common sole was 25 kJ g^?0.8 day^?1. In conclusion, the low growth of common sole fed formulated diets was related to reduced feed utilization.     

Preliminary experiments on the development of extensive culture methods for juvenile sole, Solea solea (L.)

Abstract. The effect of different levels of organic enrichment on benthic productivity was studied over a 16-week period in trays of sediment placed in a fertilized seawater pond. Primary and secondary planktonic production were also monitored. The exploitation of these sources of food by juvenile sole and their growth and survival over an 8-week period were assessed.
The colonization of the sediments showed a marked succession. Nematodes were numerically the most abundant group and reached a peak after about 8 weeks. This was followed by a peak in the abundance of epibenthic copepods after 11 weeks. The maximum numbers of poiychaetes and larger Crustacea (mainly amphipods) occurred at the end of the trial (15 weeks). The high-organic sediment supported fewer polychaetes and copepods than either the low- or medium-organic sediments. The species composition of the benthos varied both with the level of organic enrichment and with time. Peaks of zooplankton concentrations of 23 to 25 organisms/l occurred during the spring and late summer. There was some evidence of an inverse relationship between zooplankton abundance and standing crop of algae, as indicated by chlorophyll a concentrations.
Harpacticoid copepods were the dominant food item consumed by small (21-50mm total length) sole. Polychaetes, amphipods and Crangon spp. were exploited by large (61-90mm total length) sole to a much greater extent, though harpacticoid copepods were also commonly taken.
The percentage increase in length of the juvenile sole at low-, medium- and high-organic levels was 108, 146 and 152 respectively. Survival, however, was highest (100%) on the untreated sediment and lowest (57%) at the medium-organic level.     

Observations on the growth, survival and disease resistance of juvenile common sole, Solea solea (L.), fed Mytilus edulis L.

Abstract. The growth and survival of groups of juvenile sole, Solea solea (L.), fed exclusively fresh or heat-treated and frozen (stored) mussel, Mytilus edulis L., were compared and the effect of supplementing the stored mussel with one and two feeds per week of fresh mussel was assessed. Over the 9 weeks of the experiment the survival of the fish fed fresh mussel exceeded 90%. In contrast, less than 3% of those fed stored mussel alone survived. The inclusion of two feeds per week of fresh mussel increased survival to the same level as that of the groups fed only fresh mussel, though growth rates were significantly lower. The mortalities of the fish fed stored mussel were associated with an outbreak of the disease 'black patch necrosis' (BPN). The fish fed fresh mussel did not develop the symptoms of this disease despite their proximity to diseased fish and the lack of precautions to prevent its spread. The fish were not provided with a sand substrate, often considered necessary for sole ongrowing. It is suggested that a combination of adequate nutrition and attention to tank cleanliness is sufficient to avoid the occurrence of BPN and that the provision of a sand substrate is not a prerequisite for successful culture of juvenile sole.     

Feed intake as explanation for density related growth differences of common sole Solea solea

Growth of common sole Solea solea is negatively correlated to density, which affects productivity in culture and hence commercial success. Studies of individual feed intake were performed to examine growth and population dynamics at different densities. Three initial stocking densities: 1.0, 2.1 and 3.9 kg m^?2 of individually tagged sole, referred to as low density (LD), medium density and high density HD), were examined during 145 days. Despite that tank productivity (g m^?2 day^?1), was highest for the HD group, the specific growth rate (SGR) decreased significantly with increase in stocking density. Individual size variation was similar between densities, indicating that growth was not associated with hierarchy and dominant behaviour. Individual data indicated that increased density reduced the growth potential of all individuals in a population. Individual feed intake was positively correlated to both fish size and individual SGR. Feed conversion ratio was likewise positively correlated to feed intake. The relative feed intake (g feed g fish^?1) was not correlated to fish size at any density tested, but was significantly highest for the LD population. This explains a substantial part of the better growth in the LD group supported by indications of better utilization of the ingested feed.     

Identification and treatment of diseases in the common sole (Solea solea L.)

Three bacterial diseases (tailrot, furunculosis and red-spot disease) are described. A Pseudomonas was associated with the first two and a Vibrio with the third. Tailrot and furunculosis could be cured by treating the fish with antibiotics, but red-spot disease could not because of its very rapid progression and late on-set of signs. Ectoparasites probably facilitate the entry of disease organisms.     

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.     

A comparison of fatty acid composition and quality aspects of eggs and larvae from cultured and wild broodstock of common sole (Solea solea L.)

Eggs from a F₁ cultured broodstock of sole were compared with eggs from wild‐caught breeders throughout one spawning season, to evaluate if egg quality may be affected by culture‐related conditions. Fourteen batches of eggs from cultured broodstock and 17 batches from wild‐caught sole were compared with respect to fatty acid (FA) composition, egg size, fertilization rate and hatching rate. Based on a multivariate analysis of the FA profiles, it was possible to discriminate between culture and wild inheritance. Eggs from cultured broodstock had high levels of C20:1(n‐9), C18:2(n‐6) and C18:3(n‐3), whereas eggs from wild fish had high levels of C16:1(n‐7), C20:4(n‐6) and C20:5(n‐3). Differences in FA profiles were most likely related to dietary differences. Fertilization and hatching rates were generally low and lowest in eggs from cultured broodstock, but not related to FA composition. Larval growth of one batch from each group was compared. Larval growth was not correlated to broodstock origin, FA composition or egg or larval size. However, larval survival was significantly lower for larvae from cultured broodstock.