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.     

A review of the culture potential of Solea solea and S. senegalensis

Reviews in Fish Biology and Fisheries - A number of scientific studies have investigated aspects of soles(Solea soleaandS. senegalensis) ecology, population genetics and biology in their natural...     

Differential Use of Nursery Areas Within the Tagus Estuary by Sympatric Soles, Solea solea and Solea senegalensis

The spatio-temporal pattern of estuarine use by both Solea solea and Solea senegalensis was investigated between April 1995 and November 1996 by beam trawl surveys. Spatial and seasonal distribution and abundance were different for each species. The highest densities of S. solea were recorded in deeper, warmer, low salinity areas and where the sediment consisted of a high proportion of fine sand and presented a high abundance of amphipods. The 0-group individuals of this species first occurred on the nursery ground in April. Numbers peaked in June and July, and from October to April abundance was low. S. senegalensis had a wider distribution and its abundance was related to food availability. The 0-group individuals of this species occurred in the nursery areas later than S. solea, from June to August.     

A taxonomic reappraisal of the Atlanto-Mediterranean soles Solea solea, S. senegalensis and S. lascaris

Examination of morphometric characters of Solea aegyptiaca shows that it cannot be separated from Solea solea . Diagnostic characters are given to separate this species from S. senegalensis . The available data show that Solea impar and S. nasuta are junior synonyms of S. lascaris . Meristic characters of S. solea and S. lascaris vary greatly according to the geographical origin of the examined fishes, indicating the influence of temperature on the number of vertebrae and fin rays. A key is provided for the identification of the four species of the genus Solea known in the Atlanto-Mediterranean region.     

The Thymic Microenvironment of the Common Sole,Solea solea

Abstract The thymus of the sole Solea solea contained lymphoblasts and thymocytes within a network of pale and dark epithelial cells. The pale cells were characterized by tonofilaments and desmosomes and some embraced rodlet cells within their cytoplasmic processes. The dark epithelial cells had numerous electron-dense inclusions and electron-lucent vacuoles. Lymphocytes were closely associated with the plasma membrane of both types of epithelial cells and with macrophages. Breakdown of effete lymphocytes appeared to be the main function of the macrophages. Some macrophages were multinucleated. Those containing melanin granules associated with phagosomes were classified as melanomacrophages. Pigment cells including melanophores and guanophores were present along the connective tissue trabeculae and surrounding the blood vessels. A few plasma cells and mucous cells were present.     

Expanding hybrid zone between Solea aegyptiaca and Solea senegalensis: genetic evidence over two decades

Several marine hybrid zones have been described and studied during the last years. Assessing the movements of extending hybrid zones is central to improve our understanding of evolutionary processes. We have re-examined the hybrid zone between Solea aegyptiaca and Solea senegalensis that was first described 22 years ago in northern Tunisia when introgressed S. senegalensis individuals were found in the Gulf of Tunis, whereas locally caught S. aegyptiaca were genetically pure. Six population samples harvested both inside and outside the area where the two fish species coexist were genotyped for allozymes and exon-primed intron length polymorphism. Both types of markers were congruent and revealed that introgression takes place indeed in both directions. A high introgression level (36.4%) in the Bizerta lagoon and much less outside indicate that this is the main area where hybridization occurs while introgression clines towards the south in S. aegyptiaca and towards the north in S. senegalensis plead in favour of the existence of a unimodal hybrid zone. The higher introgression level calculated in the current study (when compared to 16% reported formerly) and the newly found introgressed S. aegyptiaca in Bizerta lagoon seem to indicate that the genetic exchanges occurring between the two taxa are evolving and not stabilized yet.     

Development of the Senegal sole, Solea senegalensis forebrain

The present paper deals with the ontogeny of the forebrain of the flatfish Senegal sole, Solea senegalensis, through different developmental stages before and after to metamorphosis. A first approach was made by conventional histological techniques, which allowed the determination of the main ontogenetic events. A second approach was to analyze the proliferation zones (PZ) during development and their locations, as well as the relation between them and the telencephalic asymmetry of the Senegal sole. The results show that before metamorphosis the Senegal sole goes through a fast development. The pituitary is visible 1 day after hatching (DAH), the inferior lobes of the hypothalamus appear 3 DAH, and the olfactory bulb and the differentiation between telencephalon and diencephalon are present around 4 DAH. In addition, by applying proliferating cell nuclear antigen (PCNA) immunohistochemistry by means of a monoclonal antibody against the PCNA and ABC complex, we were able to determine the PZs in the forebrain of pre- and post- metamorphic specimens. Although in both cases the PZs were similar, in premetamorphic animals they were thicker. However, PZs were observed in the pallium and subpallium, preoptic region, pretectum, epithalamus, dorsal and ventral thalamus, posterior tuberculum and hypothalamus. In all cases the PZs, mainly focusing on the telencephalon, were symmetrical in both hemispheres.     

Changes in Solea senegalensis sperm quality throughout the year

Some of the Senegalese sole (Solea senegalensis) broodstock reproductive constraints are related to sperm quality. Although they present two defined spawning season (spring and autumn), males gave semen during all the year thus an exhaustive annual sperm analysis is important to determine the seasonal changes in semen quality. Sampling was performed monthly during one year, analyzing different cellular parameters to better understand sperm quality limitations obstructing sole mass production. The percentage of progressive motile cells and their linear velocity showed a decrease from March (beginning of the first spawning season) to July (when the highest temperatures were observed), followed by a slight increase in August and October (second spawning season). DNA fragmentation values showed highest values between the two spawning seasons and decreased to the end of the year. The percentage of apoptotic cells was lowest in March (beginning of the first spawning season) and the highest in November. The percentage of cells resistant to seawater exposure presented two peaks related with both spawning seasons. There was a tendency for the semen to attain a quality peak between the beginning and the middle of the first spawning season (March-May), followed by a pronounced decrease, achieving the lowest values during the months with the highest temperature. Also, the different males present in the broodstocks reach their sperm quality peak at different times, which will result in an unequal contribution for the next generation.     

Food deprivation induces chronic stress and affects thyroid hormone metabolism in Senegalese sole (Solea senegalensis) post-larvae

In vertebrates, stress and thyroid systems interact closely, most likely because of the involvement of both systems in energy metabolism. However, studies on these interactions, especially during larval development, are scarce. Recently, cDNAs coding for corticotropin-releasing hormone (CRH) and CRH-binding protein (CRH-BP), two key players in the regulation of the neuroendocrine stress response, were characterized for the flatfish Senegalese sole (Solea senegalensis). To investigate the involvement of stress and thyroid systems in this species, the effects of food deprivation during early development of S. senegalensis were assessed. Growth was arrested in food-deprived post-larvae, which was also reflected by decreased carbon and nitrogen contents, indicating increased catabolism. Food deprivation induces chronic stress, as illustrated by enhanced whole-body cortisol levels, as well as an up regulation of crh and a decrease of crh-bp expression levels. Furthermore, whole-body total T3 concentrations of food-deprived post-larvae were reduced, although tshβ subunit expression levels remained unaffected. Our results show that food deprivation is a chronic stressor that induces energy-releasing catabolic processes that compensate for the reduced energy intake, and inhibits anabolic processes via the peripheral thyroid system.     

Multivariate analysis of genetic exchanges between Solea aegyptiaca and Solea senegalensis (Teleosts, Soleidae)

Electrophoretic data from different populations of the teleosts Solea senegalensis, S. aegyptiaca and S. vulgaris were analysed using multivariate analysis. This confirmed that Solea vulgaris is very different genetically and isolated from both senegalensis and aegyptiaca , and that the latter two forms are also well differentiated. The presence of senegalensis alleles in the aegyptiaca population of the Golfe-du-Lion, and reciprocally, aegyptiaca alleles in the senegalensis population of the Gulf of Tunis, suggests that genetic exchange occurs between them. The association of these alleles (gametic disequilibria) and the existence of hybrid individuals show that these exchanges are an actual process rather than a consequence of 'fossil' gene flow. Furthermore, the genetic introgression seems to be asymmetrical in the two regions studied where they come into contact.     

The effect of hypoxia on ventilation frequency in startled common sole Solea solea

Ventilation frequency (F_V) in motionless common sole Solea solea was measured before and after a startling stimulus in normoxia and in hypoxia (15% air saturation). Startling reduced F_V in normoxia (from mean ±s.e. 41 ± 3·3 beats min^?1 to near zero, i.e. 2·0 ± 1·8 beats min^?1) and in hypoxia (from mean ±s.e. 80 ± 4·4 to 58·8 ± 12·9 beats min^?1). It is suggested that the maintenance of high F_V in hypoxia may increase the probability of detection by predators compared to normoxia.     

Habitat specific growth rates and condition indices for the sympatric soles Solea solea (Linnaeus, 1758) and Solea senegalensis Kaup 1858, in the Tagus estuary, Portugal, based on otolith daily increments and RNA-DNA ratio

Habitat specific growth rates and condition indices were estimated for Solea solea and Solea senegalensis, in two nursery areas within the Tagus estuary, at the end of the estuarine colonization process, in 2005. While in the uppermost nursery area the two species of sole live in sympatry, in the lower nursery only S. senegalensis is present. Daily increments of left lapillar otoliths were used to estimate age (in days) and determine growth rates (mm per day). Condition indices were assessed through RNA‐DNA ratio in muscle samples. Growth rates were higher for S. senegalensis (0.970and 1.180 mm per day in nursery A and B, respectively) than for S. solea (0.767 mm per day in nursery A). Growth rates of S. senegalensis from the uppermost nursery area were lower when compared to those obtained for the other nursery. The RNA/DNA condition index followed the general trend given by the growth rate estimates, i.e. values were higher for S. senegalensis than for S. solea. However, no significant differences were detected in S. senegalensis from the two nurseries. Larger variations in salinity (10‰ amplitude in the uppermost nursery vs 0.2‰ in the lower nursery) and highest pollution loads may be important factors lowering the habitat quality of the uppermost nursery in comparison to the lower nursery. The use of growth rate estimates based on otolith readings and the RNA/DNA index as tools for habitat quality assessment was discussed.     

Ultrastructural study on the intestine of Senegal sole, Solea senegalensis

The intestinal epithelium of Senegal sole, Solea senegalensis Kaup is composed of three main cell types: epithelial, goblet and rodlet. The cytoplasm of columnar epithelial cells – enterocytes – has spherical lipid droplets. The dominant feature throughout the intestinal mucosa was goblet cells filled with numerous mucous droplets of high density. The cytoplasm of the rodlet cells contained peripheral filamentous, pycnotic nuclei, and numerous cytoplasmic inclusions (rodlets), with a very dense cylindrical core surrounded by flocculent material. Some physiological implications related to ultrastructural features of the intestine are also discussed.     

Histological and histochemical observations in the stomach of the Senegal sole, Solea senegalensis

An histological and histochemical study was conducted on the stomach of adult Senegal sole, Solea senegalensis specimens. The stomach was made up of four distinct layers: mucosa, lamina propria-submucosa-, muscularis and serosa. Surface epithelial, glandular and rodlet cells were present in the mucosa. Cells of the columnar epithelium contained a basal nucleus. Numerous mitochondria, granular endoplasmic reticulum and Golgi apparatus consisting of several parallel cisternae and vesicles were observed in the cytoplasm of these cells. The lysosomes were small, round and dense. The gastric glands were numerous in the pyloric and fundic regions but absent in the cardiac stomach. These glands were formed by two cell-types: light and dark cells. The light cells were characterised by numerous mitochondria, while dark cells had slightly fewer mitochondria and a tubulo-vesicular system. Rodlet cells similar to those observed in other teleostean fish were present among the epithelial cells. Although the epithelial cells of the mucosa contained a weak presence of neutral and acid mucopolysaccharides/mucosubstances, these substances were abundant in the lamina propria-submucosa. Proteins rich in arginine, lysine, cysteine and cystine were rarely present in the mucosa and lamina propria-submucosa of stomach, while proteins rich in tyrosine were abundant in these layers. Acid phosphatase, and ATP-ase (pH 7.2 and 9.4) activities were detected in the mucosa and lamina propria-submucosa. Alkaline phosphatase activity was not detected.     

Osmoregulatory response of Senegalese sole (Solea senegalensis) to changes in environmental salinity

The osmoregulatory response of Senegalese sole (Solea senegalensis, Kaup 1858) to 14-day exposure and throughout 17-day exposure to different environmental salinities was investigated. A linear relationship was observed between environmental salinity and gill Na(+),K(+)-ATPase activity whereas kidney Na(+),K(+)-ATPase activity was unaffected. Two osmoregulatory periods could be distinguished according to variations in plasma osmolality: an adjustment period and a chronic regulatory period. No major changes in plasma osmolality and ions levels were registered at the end of the 14- to 17-day exposure period, indicating an efficient adaptation of the osmoregulatory system. Plasma levels of glucose and lactate were elevated in hypersaline water, indicating the importance of these energy substrates in these environments. Glucose was increased during hyper-osmoregulation but only in the adjustment period. Cortisol proved to be a good indicator of chronic stress and stress induced by transfer to the different osmotic conditions. This work shows that S. senegalensis is able to acclimate to different osmotic conditions during short-term exposure.