Metabolism in marine flatfish. II. Protein digestion in Dover sole (Solea solea L.)

The digestive tracts of adult and juvenile Dover sole were examined for protease activities. A pepsin-like protease with an optimal pH value of 1.7 predominated in the stomach region, but the main endoprotease action in the foregut, midgut and hindgut regions was optimal in the range of pH 9.5-10.5 and showed good activity towards elastin orcein. Experiments using synthetic substrates suggested the presence of chymotrypsin- and trypsin-like activities optimal between pH 7 and 8. Collagenase activity was also shown to exist in this pH region. The presence of enzymes corresponding to carboxypeptidases a and b and leucine aminopeptidase was indicated. The possible significance of these results to the farming of Dover sole is discussed.     

Redescription of the life cycle of Haemogregarina simondi (Laveran and Mesnil, 1901) in its vertebrate host the marine fish Solea solea (Linnaeus).

The life cycle of Haemogregarina simondi is described in its vertebrate host the marine flatfish Solea solea. An intraleucocytic schizogony is followed by an intraerythrocytic schizogony giving rise to eight gametocytes. A differentiation into micro- and macro-gametocytes was also observed and thus confirms the results of other authors for H. aeglefini, H. bigemina, and H. sachai. It is postulated that most if not all of the haemogregarines of marine fish undergo similar life cycles as the one described here.     

Metabolism in marine flatfish--III. Measurement of elastase activity in the digestive tract of Dover sole (Solea solea L.)

A critical assessment of different methods for measuring elastase activity in crude preparations has been made using whole intestinal homogenates of Dover sole. The use of the natural substrate elastin or its dyed derivatives gave optimal pH values in the alkaline region (pH 9.4-9.8) whereas artificial substrates showed optimal hydrolysis nearer neutrality in the region pH 8.1-8.2. Exoproteases may interfere with certain assay procedures. The properties of Dover sole elastase have been further investigated using chromatographic techniques which indicated that the main elastase activity has a molecular weight of approximately 19,500 and an isoelectric point in the region of pH 5.7.     

Interaction between exopolysaccharide and oxygenation levels on habitat selection in the sole Solea solea (L.)

A habitat selection experiment was conducted to examine the behavioural response of sole Solea solea to a combination of sediment quality (exopolysaccharides, EPS-free, i.e. 0 mg l⁻¹ and EPS-rich, i.e. 4 mg l⁻¹) and water oxygenation level (100 and 35% air saturation). The distribution of sole was influenced differently by the type of substratum depending on the water oxygenation level. In normoxia, sole settled preferentially on sand whereas under hypoxic conditions, sole settled preferentially on the muddy substratum. In order to explain these apparently counter-intuitive observations, it is proposed that, via cutaneous respiration, young sole are able to take advantage of the large quantities of oxygen produced by microphytobenthic organisms present in the upper few millimetres of muddy substratum.     

Chemical nature of feeding stimulants for the juvenile Dover sole, Solea solea (L.)

Juvenile Dover sole, Solea solea , were weaned from a live food, Artemia salina nauplii, on to a casein-based particulate diet flavoured with flesh of the mussel, Mytilus edulis . These fish would not accept an unflavoured casein-based diet but readily ate the diet flavoured with either mussel flesh or a mixture of pure chemicals whose composition was based on an analysis of the low-molecular weight fraction of mussel flesh. The rate of growth and survival over a seventy-seven day period was essentially the same on either of the flavoured diets. The active constituent in the mixture of pure chemicals was identified as glycine betaine for fish of wet weight exceeding 50g while glycine betaine with certain L-amino-acids was required for fish of about 2.5 g wet weight. These results are discussed in relation to the known feeding behaviour and food preferences of the wild Dover sole.     

An electron microscopic examination of the gastrointestinal epithelium in Dover sole, Solea solea (L.)

The gastrointestinal tracts of adult and juvenile Dover sole, Solea solea (L.), were examined using scanning (SEM) and transmission electron microscopy (TEM). SEM showed little differentiation of the internal morphology of the gastrointestinal tract in adult fish, with longitudinally arranged mucosal folds present in all gut regions. Mucosal folds had a similar arrangement to that in the goldfish. Goblet cells were identified in the mucosal epithelium in all regions of the gut while microscopic ducts/pores of possible pancreatic origin were observed in the foregut region. SEM of juvenile gut samples showed a similar arrangement of longitudinal mucosal folds to that found in the adult fish. There was no visible evidence of goblet cells or secretory ducts/pores in any region of the juvenile gastrointestinal tract.
In TEM it was observed that apical microvilli were a feature of epithelial cells from all regions of the gastrointestinal tract in adult and juvenile Dover sole. Cells from the distal regions of the adult and juvenile gut showed invaginations and vacuolation of the apical cytoplasm. A high degree of vacuolation in cells from the juvenile hindgut-rectum indicated the possible occurrence of intracellular digestion of absorbed nutrients in this gut region.     

A histopathological report of some epidermal anomalies of Dover sole, Solea solea L., and other flatfish species in coastal waters off south-east England

The gross pathological and histological changes of typical examples of epidermal anomalies of Dover sole, Solea solea L., and other flatfish from the sewage dumping areas of the Thames Estuary and two 'control' areas are described. Five per cent of flatfish showed anomalies including trawl damage abrasions, fin-rot, ulcers, nodules and tumours, lymphocystis and skeletal anomalies. Many of the anomalies suggested a traumatic aetiology and were often chronic. There was no significant difference in disease incidence between the areas sampled, except more evidence of lymphocystis in one of the control areas.     

Movements of juvenile Dover sole, Solea solea (L.), in the Tamar Estuary, South-western England

Solea solea start to appear in the Tamar Estuary in April–May when they are 10 mm long. The majority of young sole move into the estuary in June–July. Most sole leave the estuary towards the end of their second year in October–November, when they have reached a total length of 150–200 mm. The young O-group fish remain in the main channel, whereas the I-group move with the tide onto the mud-flats.
Approximately 7000 fish were marked by freeze-branding or dye-injection. The recaptures showed that there was an up-estuary migration in May–June. Most of the recaptures were taken at the site of original capture and there was only a limited movement of fish between adjacent mud-flat areas. Average growth rate tends to be greater in sole inhabiting the upper reaches of the estuary.     

The influence of sand on the estimation of resting metabolic rate of juvenile sole, Solea solea (L.)

The influence of a sandy substrate on the estimation of the resting metabolic rate of juvenile sole was determined using a static type of respirometer. Oxygen consumption of fish deprived of sand was almost double that of fish provided with sand.     

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%).     

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.     

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.     

Observations on the ultrastructure of the carp liver (Cyprinus carpio L.)

The paper presents information about the fine structure of the sinusoids, the space of Dissé, the development of the bile canaliculi and some compartments of the hepatocytes in the liver of the carp. The sinusoids are covered completely by flat endothel cells. The plasma of these cells contains numerous vesicles. The endothelial cells possess plasmatic processes, which extend into the space of Dissé. The fine structure of the space of Dissé corresponds to that of mammals, the existence of fibrebundles included. The bile canaliculi don't develop intracellularly as described by other authors. They run intercellularly as in mammals, but they form diverticles which reach into the plasma sideways. The rough ER was found in two types. Outwardly the liver is limited by a layer of connective tissue existing in two different layers.     

The influence of prey size,sediment thickness and fish size on consumption in common sole (Solea solea L.)

This study determined prey consumption in common sole as a function of prey size (0–0.5, 1–1.5, 2–2.5 and 4–5 g), sediment thickness (20 cm and 2 cm) and fish size (50 g, 125 g or 300 g). Prey consumption (in numbers of prey eaten per fish per day) was reduced with increasing prey size and sediment thickness, and was increased with increasing fish size (p < .001 for all factors). All 3 factors showed significant two way interactions (p < .001) when expressed in numbers of prey eaten. Prey consumption decreased with prey size when prey could not escape by burying (2 cm of sediment thickness) irrespective of fish size. We suggest that increasing effort to ingest and handle larger prey played a role. Prey consumption increased with fish size when prey could not bury (2 cm of sediment thickness). However, when prey was able to bury (at 20 cm sediment thickness) prey consumption was similar irrespective of fish size (p < .001 for interaction fish size × sediment). This interaction suggests that with increasing fish size there is an increasing mismatch between foraging adaptation and prey burial depth. This may explain the dominance of crustaceans in the diet of adult common sole in nature, despite the high abundance of polychaetes.     

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.     

Expression of myofibrillar proteins and parvalbumin isoforms during the development of a flatfish,the common sole Solea solea: comparison with the turbot Scophthalmus maximus

Developmental changes in myofibrillar protein and parvalbumin isoform composition were investigated in the myotomal muscle of the flatfish Solea solea, characterized by a very brief metamorphic stage. Results were compared with previously obtained data on another pleuronectiform teleost, the turbot (Scophthalmus maximus), displaying prolonged metamorphosis. Electrophoretically measurable changes in myofibrillar proteins and parvalbumins were detected late in the sole, after completion of metamorphosis. In the course of development, muscles showed the usual sequential synthesis of isoforms of the myofibrillar proteins myosin light chain LC2, troponin-T, and troponin-I. An adult parvalbumin isoform (PA III) was found to predominate during sole growth. The two flatfish were characterized by highly species-specific parvalbumin isoforms. Compared with turbot, the profiles of the myofibrillar subunits and parvalbumin isoforms varied little in the course of sole development. The early appearance of adult traits might be correlated with the brevity of metamorphosis of this fish.     

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.