Effect of temperature and salinity on the gastric evacuation of juvenile sole Solea solea and Solea senegalensis

The juveniles of Senegal sole, Solea senegalensis, Kaup 1858, and common sole, Solea solea (Linnaeus 1758) concentrate in estuarine and coastal nurseries of widely differing temperatures and salinities. Yet, little is known about the effect of these physiologically important variables on the gastric evacuation rates of these species. Gastric evacuation experiments were performed on juveniles of S. senegalensis and S. solea. Three temperatures were tested, 26, 20 and 14°C at a salinity of 35‰. A low salinity experiment was also carried out at 15‰, at 26°C. Experimental conditions intended to reflect conditions in estuarine and coastal nurseries where juveniles of these species spend their first years of life. The relation between stomach contents and time was best described by exponential regression models for both species. An analysis of covariance (ancova ) was performed in order to test differences in evacuation rate due to temperature and salinity (slope of evacuation time against stomach contents) for each species. While increasing temperature increased evacuation rates in both species (although not at 26°C in S. solea), the effect of low salinity differed among species, leading to a decrease in gastric evacuation rate in that of S. senegalensis and an increase in S. solea. Differences in gastric evacuation rate between species were related to its metabolic optimums and to its distribution in the nursery area where fish were captured. Implications for the habitat use of estuarine and coastal nurseries are discussed.     

Development and characterization of microsatellites from Senegal sole (Solea senegalensis)

To assist in the domestication of the sole fish Solea senegalensis, 15 microsatellites were developed from its genome (13 di‐ and two trinucleotide). These loci, along with three from S. solea that cross‐amplified, were characterized on a sample of 20 individuals of S. senegalensis from a hatchery stock. All loci were polymorphic displaying from two to 15 alleles/locus (mean 6.5). The results obtained from the hatchery population screening indicate that they might be useful for studies of genetic structuring and/or kinship analysis in S. senegalensis.     

Growth variability of juvenile soles Solea solea and Solea senegalensis, and comparison with RNA : DNA ratios in the Tagus estuary, Portugal

Growth variability and condition of juvenile soles Solea solea and Solea senegalensis , were assessed through RNA : DNA estimates and compared to absolute growth rates. Higher mean cohort RNA : DNA ratios were observed for cohort I at the beginning of estuarine occurrence for both species (4·42 and 4·87, for S. solea and S. senegalensis respectively). Despite different estuarine colonization habits, no significant differences were observed between RNA : DNA monthly variation for both sole species within the same year ( P  > 0·05 for 2003 and 2004). Juvenile S. senegalensis showed significant differences between RNA : DNA ratios obtained for the two nursery areas ( P  < 0·001). The decrease of seasonal growth rates with fish age was similar to seasonal variation of mean RNA : DNA values. Thus the RNA : DNA pattern of juvenile S. solea and S. senegalensis reflected growth and estuarine colonization patterns.     

Biological availability and humic properties of dissolved organic carbon in Lake Balaton (Hungary)

The nursery role of the Mondego estuary for marine fish species was studied between June 2003 and May 2004. The spatial and temporal distribution and abundance patterns of 0-group Dicentrarchus labrax (Linnaeus, 1758), Platichthys flesus (Linnaeus, 1758) and Solea solea (Linnaeus, 1758) were analyzed based on monthly sampling surveys in five stations along the estuarine gradient. Fishing took place during the night at low water of spring tides, using a 2 m beam trawl. The spatial patterns of estuarine colonization were different according to species. D. labrax showed a wider distribution, but the main nursery ground was the same as for S. solea. Highest densities of S. solea juveniles were found in oligohaline areas, with muddy bottoms and high benthic invertebrates availability, while P. flesus occurred mainly in the sandy uppermost areas. D. labrax was found in both these areas. Fish abundance in the estuary mainly reflected seasonal changes.     

A review of the culture potential of <Emphasis Type="Italic">Solea solea</Emphasis> and <Emphasis Type="Italic">S. senegalensis</Emphasis>

A number of scientific studies have investigated aspects of soles(Solea soleaandS. senegalensis) ecology, population genetics and biology in their natural environment, and the species have been extensively studied in captivity during the last decade. Studies on the genetic population structure of sole indicate that several distinct breeding populations exist within its distributional range in European waters. Recent studies suggest a phylogenetic relatedness ofS. soleaand S. senegalensis, being found as closest sister lineages in most reconstructions. However, studies on molecular genetics and morphological traits give diagnostic differences that consistently lead to their taxonomic separation at the specific rank. Studies show that sole spawn readily in captivity, and the buoyant, fertilized eggs are easily collected. Stocking density during maturation should be 1–1.5kg/m², and temperature should be kept above 16°C (S. senegalensis) or between 8 and 12°C (S. solea). In nature, the onset of spawning is related to a rise in temperature occurring during spring (March–June). Salinity should be kept constant around 33–35 and the fish reared under simulated natural photoperiod (LDN). In other cultured flatfish species, a change in the photoperiod is the key environmental signal used to manipulate and control maturation, but at present time there are no published work that verifies or contradicts this for either S. senegalensisor S. solea. Studies indicate that a mixture of inert and live food may increase the weaning success of sole fry, and this can be further enhanced by using attractants in the dry feed. Future experiments are needed to determine the ideal time to commence weaning and determine the minimum duration of this period. Studies on alternative feeding strategies are also required. The effect of temperature and photoperiod on juvenile growth has not been studied systematically in neither of the two species and the relative importance of a direct photoperiod effect on growth in sole therefore remains to be defined.     

Comparative xenobiotic metabolism capacities and pesticide sensitivity in adults of Solea solea and Solea senegalensis

The measurement of enzymatic activities involved in xenobiotic biotransformation was carried out in adults of Solea solea and Solea senegalensis. The hepatic enzymes analysed were cytochrome P450 (CYP) related activities using eight fluorometric substrates and carboxylesterases (CbE). The conjugating activities of glutathione S-transferase (GST) and UPD-glucuronosyltransferase (UDPGT) were also assessed. Specific mammalian inhibitors were used as diagnostic tools for related activities of CYP1A (α-naphthoflavone; αNF), CYP2B6 and CYP2C19 (ticlopidine) and CYP3A4 (ketoconazole). The in vitro sensitivity to organophosphorous pesticides (OP) was tested in the S10 homogenate of brain (acetylcholinesterase-AChE) and liver (CbE). Furthermore, the pesticide chlorpyrifos oxon (CLPO) was used to explore the OP sensitivity of CbE of both species in two subcellular fractions (microsomes and cytosol), using two substrates. Overall, only two parameters confirmed species differences: EROD and cytosolic CbE being significantly elevated (p < 0.05) in the common sole, S. solea. A high inhibition of CYP1A related activities using several fluorometric substrates (ER, MR and CEC) after in vitro incubation with αNF confirmed all measure CYP1A1-related activities whereas ketoconazole was more specific for BFCOD (CYP3A4). Pesticide sensitivity was similar for brain AChE but hepatic CbE had a protective role that was species and pesticide dependent.     

Niche overlap between juvenile flatfishes, Platichthys flesus and Solea solea, in a southern European estuary and adjacent coastal waters

The distribution and abundance patterns as well as the feeding ecology of two flatfishes, Platichthys flesus (Linnaeus, 1758) and Solea solea (Linnaeus, 1758), were studied in the Douro estuary and adjacent coastal waters (Portugal) in order to evaluate the niche overlap between these species. Fish were collected during sampling surveys conducted every 2 months between November 2000 and March 2002 using a 12‐m otter‐trawl with 18 mm stretched mesh size, at 12 sites within the estuary and six sites in the adjacent coastal area. The highest densities of P. flesus were registered in the middle estuary; a peak density of 9.12 ind 1000 m^?2 was obtained in October 2001. Solea solea densities were low compared with P. flesus; the highest values were also recorded in the middle estuary in October 2001. For both species, the proportion of juveniles was above 90% within the estuary. Highest densities of P. flesus and S. solea were recorded at sites with low water depth and high densities of crustaceans and polychaetes, the main food items in the diet of these species. High values of spatial and diet niche overlap were found between these two flatfishes (0.97 and 0.92, respectively).     

Daily rhythms in the somatotropic axis of Senegalese sole (Solea senegalensis): The time of day influences the response to GH administration

Growth factors in vertebrates display daily rhythms, which, while widely described in mammals, are still poorly understood in teleost fish. Here, we investigated the existence of daily rhythms in the somatotropic axis of the flatfish Solea senegalensis. In a first experiment, daily rhythms of the expression of pituitary adenylate cyclase–activating polypeptide (pacap), growth hormone (gh), insulin-like growth factor 1 (igf1) and its receptor (igf1r) were analyzed under a 12:12 h light:dark cycle. All genes displayed daily rhythms with the acrophases of pacap, gh and igf1 located in the second half of the dark phase (ZT 20:28–0:04 h), whereas the acrophase of igf1r was located around mid-light (ZT 5:33 h). In a second experiment, the influence of the time of day (mid-light, ML, versus mid-darkness, MD) of GH administration on the expression of these factors and on plasma glucose levels was tested. The response observed depended on the time of injection: the strongest effects were observed at MD, when GH administration significantly reduced pituitary gh and enhanced liver igf1 expression. These results provide the first evidence of daily rhythms and differential day/night effects in growth factors in S. senegalensis, suggesting new insights for investigating the physiology of growth and possible applications to improve fish aquaculture.     

Lipid‐based indicators of nutritional condition in juvenile sole Solea solea

Effects of the feeding level on juvenile Solea solea (Linnaeus, 1758) lipid‐related indicators of nutritional condition were assessed in a 25‐day trial experiment. Morphometric indices (K and HSI), liver lipid content and fatty acids (FA) clusters were good indicators of the feeding level, while individual FA showed highly dynamic variation patterns. Additionally, liver indices were more sensitive to feeding stress than were muscle measurements. HSI determination (and K) is fairly straightforward, with lower costs and simple procedures. Nevertheless, liver lipid content is also an important indicator of the feeding level and constitutes a direct measurement of food utilization and energy storage capacity. The individual variability and complex dynamics of FA with the feeding level are disadvantageous for use in FA analysis even for early‐warning signals of feed limitation. Overall, S. solea nutritional condition can be suitably assessed by morphometric indices and lipid content, especially considering liver measurements (HSI and liver lipid content), provided that the fish development stage is accounted for (i.e. gonad development and reproductive cycle).     

Influence of sex, age and season on the feeding habits of the flatfish Solea senegalensis

Synopsis The Senegal sole Solea senegalensis is a commercially valuable fish and it is beginning to be cultured, in an extensive way, in fish farms in southern European countries. Little is known about its feeding habits, unlike other Solea species such as the common sole Solea solea. This paper studies the feeding habits of a wild population of Senegal sole. Differences according to sex, age and season were statistically analyzed. A total of 376 fish, aged between two and six years old, were studied over a single year. Twenty eight different families of prey were identified, belonging, in order of abundance, to crustaceans, polychaetes and molluscs. The Senegal sole trophic profile (preys items with a Simpson's dominance index 2) was: Glyceridae, Nephtydidae, Onuphidae, Apseudidae, Ampeliscidae and Upogebiidae. Feeding habits of Senegal sole were significantly influenced by sex, age and season, with crustaceans being the prey most affected.This paper is dedicated to the memory of Daniel Ray Ogilvie. who died 7 January 1995.     

Isolation of polymorphic DNA microsatellites in the common sole Solea vulgaris

A microsatellite‐enriched genomic library was obtained from the common sole, Solea vulgaris, and seven polymorphic dinucleotide markers were successfully optimized. These markers showed levels of expected heterozygosity ranging from 0.55 to 0.83 and allele number ranging from eight to 12. Three of these markers were also found to successfully amplify in the closely related Solea senegalensis and can be employed to define population genetic structure of the two Solea species and for inferring stock origins.     

Effects of acute handling stress on cerebral monoaminergic neurotransmitters in juvenile Senegalese sole Solea senegalensis

Juvenile Senegalese sole Solea senegalensis were subjected for short periods to two different types of handling‐related stress: air exposure stress and net handling stress. The S. senegalensis were sacrificed 2 and 24 h after the stress events and the levels of serotonin (5‐HT), noradrenaline (NA), dopamine (DA) and their respective major metabolites, 5‐hydroxyindoleacetic acid (5‐HIAA), 3‐methoxy‐4‐hydroxyphenylglycol (MHPG) and 3,4‐dihydroxyphenylacetic acid (DOPAC), were measured in three brain regions (telencephalon, hypothalamus and optic tectum) and compared with those in control, non‐stressed S. senegalensis. Neither type of stress caused any significant alteration of serotoninergic activity (5‐HIAA:5‐HT ratio) or NA levels. Dopaminergic activity (DOPAC:DA ratio) was lower in stressed fish in all of the brain regions studied. For both air exposure stress and net handling stress, DA levels were significantly higher (P < 0·05) than in the control S. senegalensis. In addition, the higher DA levels after net handling stress were always significantly higher (P < 0·05) than those observed after acute air exposure stress, except in the telencephalon after 24 h. The significantly lower DOPAC:DA ratio (P < 0·05) in all of the brain regions studied was only observed in response to net handling stress.     

Parasitic copepods of the common sole, Solea solea (L.), from the Eastern Mediterranean coast of Turkey

There is increasing interest in the common sole, Solea solea (Linnaeus), as an alternative fish species in aquaculture in the Mediterranean region, and parasitic copepods are a potential hazard for farmed finfish. This paper provides taxonomic information on two species of sea lice (family Caligidae) collected from S. solea in eastern Mediterranean waters off the Turkish coast. Caligus brevicaudatus A. Scott, 1901 and Caligus apodus (Brian, 1924) were both found and this is the first report of C. brevicaudatus in Turkish waters. The discovery of C. apodus on S. solea is a new host record. Key diagnostic characters of both species are reported, supported by light and scanning electron microscopy observations. During a 12-month survey a prevalence of 28% was recorded for C. brevicaudatus, whereas for C. apodus peak prevalence was much lower (3%).     

Estuarine colonization, population structure and nursery functioning for 0-group sea bass (Dicentrarchus labrax), flounder (Platichthys flesus) and sole (Solea solea) in a mesotidal temperate estuary

The function of the Mondego estuary as a fish nursery habitat was investigated from June 2003 to June 2004 by comparing the timing of estuarine colonization with juveniles of sea bass Dicentrarchus labrax, flounder Platichthys flesus, and sole Solea solea, while also analysing their population structure, growth and diet composition. Differences in the onset of estuarine colonization were observed, since sole juveniles were the first to enter the estuary (in January), followed by flounder in April and sea bass in June. The estuarine population of these species consisted of several age‐groups, although the majority of individuals belonged to age‐groups 0 and 1. The growth rates determined for 0‐group fish were within the range of those reported for other European estuarine systems. Some differences were also recognized regarding the timing of estuarine colonization and the length of the growing season. Diet of 0‐group sea bass consisted mainly of Crustacea, Polychaeta and Mollusca. Flounder juveniles fed chiefly on Amphipoda (especially Corophium spp.), with Polychaeta, Isopoda and Decapoda also being common prey. The diet of 0‐group sole was dominated by Polychaeta, with Amphipoda, Mollusca and Decapoda ranking highest, with other important benthic organisms also being present. Dietary overlap among these species was relatively low.     

An immunocytochemical study of pituitary cells of the Senegalese sole, Solea senegalensis (Kaup 1858)

Different antisera directed against mammalian and piscine pituitary hormones, as well as a battery of various conventional histochemical techniques (PAS, Alcian Blue pH 2.5, Bromophenol Blue) and lectins, were used to identify the different hormonal cell types in the pituitary of the Senegalese sole, Solea senegalensis. Prolactin and adrenocorticotrophic cells were located in the rostral pars distalis of the pituitary. Gonadotrophic, thyrotrophic and growth hormone cells were distributed in the proximal pars distalis, but gonadotrophic cells appear also at the border of the pars intermedia. Somatolactin cells, as well as α-melanotrophic cells were located in the pars intermedia of the Solea senegalensis pituitary. The PAS reaction was positive in somatolactin cells, which were unreactive with the lead--Haematoxylin technique, whereas melanotrophic cells were positive. Glycoproteins containing mannose and/or glucose, as well as N-acetyl-glucosamine and sialic acid sugar residues, are synthesized and secreted by gonadotrophic, thyrotrophic and somatolactin cells. Adrenocor ticotrophic cells and, especially, the amphiphilic somatolactin and acidophilic growth hormone cells were stained with the Bromophenol Blue technique that identifies proteins in general, but adrenocorticotrophic and growth hormone cells were unreactive towards PAS, Alcian Blue pH 2.5 and lectins (Con A and WGA) This revised version was published online in November 2006 with corrections to the Cover Date.     

Comparison of growth and condition indices of juvenile flatfish in differentcoastal nursery grounds

Coastal and estuarine ecosystems in the eastern channel and southern bight of the North Sea provide nursery habitats for juvenile fishes. We examined the age 0-group juveniles of three flatfish speciesSolea solea, Limanda limanda and Pleuronectes platessa, collected in five nursery areas with different characteristics (three sites located near small estuaries and two affected by important inputs of industrial effluents), to evaluate habitat influence on their growth and condition. We measured a biochemical index (RNA:DNA ratio), a morphometric index (Fultons K condition index), plus a recent growth index (marginal otolith increment width) on each individual (about 3months old), collected during surveys in autumn 1999. The three indices displayed few significant differences among the five nursery sites and different patterns for each species. We suggest that the investigated nursery areas provide habitats of equivalent quality for the age 0-group juvenile flatfishes in spite of different anthropogenic disturbances. On the other hand, this study focuses on the importance of using different biological indicators to assess habitat quality and environmental stressors in coastal areas.     

0-group flatfish growth conditions on a nursery ground (Bay of Canche, Eastern English Channel)

The settlement and growth conditions of three 0-group flatfish species, sole (Solea solea L.), plaice (Pleuronectes platessa L.) and dab (Limanda limanda L.) in the Bay of Canche, French coast of the Eastern English Channel, were investigated during summer 1997. 0-group dab were the more abundant of the three species (75.4%) followed by plaice (21%) and sole (3.6%). Analyses of fish size distribution indicated that settlement of plaice occurred before sole and dab. Growth of sole was faster than that of plaice, which in turn was faster than that of dab (0.68, 0.43 and 0.33 mm d^?1 respectively). Sole differed from plaice and dab by their larger mean length attained at the end of their first summer stay in the nursery ground. Growth performances of 0-group sole and plaice were analysed by comparing estimated growth in the field with predicted maximum growth according to temperature-growth rate models from experimental studies of growth with unlimited food supply. The data of this study suggest that plaice growth may have been limited during late summer, whereas sole growth does appear to have been determined only by water temperature.     

Connectivity between estuaries and marine environment: Integrating metrics to assess estuarine nursery function

Natural or anthropogenic induced variations in estuaries and the dynamics of marine fish populations potentially promote differences in connectivity between estuaries and marine areas, i.e. in their importance as nursery grounds. Within this context, an integrated assessment of the differential nursery function of the main estuaries along the Portuguese coast for commercial fish species common sole Solea solea, Senegalese sole Solea senegalensis, flounder Platichthys flesus and sea bass Dicentrarchus labrax was performed through several indicators based on available data. Contribution of individual estuaries to marine subpopulations was measured with potential metrics (juvenile density, habitat quantity, juvenile number and habitat quality within estuaries) and effective metrics (estuarine source of young adults in marine environment measured via otolith elemental fingerprints). The relationship between the two types of metrics was also assessed. Estuaries identified as important nursery and/or effective juvenile habitat (EJH) differed with species and no single estuary was best for all, highlighting species-specific regulation of nursery function. Multiple species assessment of nursery and EJH function differed among estuaries. Management and conservation of estuaries should focus on sites with higher contributions to adult subpopulations of multiple species. The importance of defining precise scientific and management objectives was emphasized by the different rankings of estuaries obtained with nursery or EJH criteria. Potential and effective contribution of estuaries were not significantly correlated, but in a quantitative analysis juvenile densities and number of juveniles seem related with effective contribution in some species. An agreement between potential and effective contributions of estuaries is concurrent with the acknowledged minor role of juvenile stage processes in regulation of recruitment to adult subpopulations.     

An immunocytochemical study of pituitary cells of the Senegalese sole, Solea senegalensis (Kaup 1858)

Different antisera directed against mammalian and piscine pituitary hormones, as well as a battery of various conventional histochemical techniques (PAS, Alcian Blue pH 2.5, Bromophenol Blue) and lectins, were used to identify the different hormonal cell types in the pituitary of the Senegalese sole, Solea senegalensis. Prolactin and adrenocorticotrophic cells were located in the rostral pars distalis of the pituitary. Gonadotrophic, thyrotrophic and growth hormone cells were distributed in the proximal pars distalis, but gonadotrophic cells appear also at the border of the pars intermedia. Somatolactin cells, as well as α-melanotrophic cells were located in the pars intermedia of the Solea senegalensis pituitary. The PAS reaction was positive in somatolactin cells, which were unreactive with the lead--Haematoxylin technique, whereas melanotrophic cells were positive. Glycoproteins containing mannose and/or glucose, as well as N-acetyl-glucosamine and sialic acid sugar residues, are synthesized and secreted by gonadotrophic, thyrotrophic and somatolactin cells. Adrenocor ticotrophic cells and, especially, the amphiphilic somatolactin and acidophilic growth hormone cells were stained with the Bromophenol Blue technique that identifies proteins in general, but adrenocorticotrophic and growth hormone cells were unreactive towards PAS, Alcian Blue pH 2.5 and lectins (Con A and WGA)