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.     

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.     

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%).     

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.     

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.     

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.     

The intestinal microflora of farmed Dover sole (Solea solea) at different stages of fish development

The bacterial flora in the intestines of farmed Dover sole ( Solea solea L.) was investigated at different stages of fish development in relation to different diets fed under farming conditions. The flora of water and diets were also analyzed. The dominant generic group isolated from all water samples examined was Pseudomonas Gp IV/ Alcaligenes. The same generic group was dominant in homogenized pelagic larvae indicating a relationship between the microflora of those young fish and that of tank water. In older fish a steady increase in the percentage incidence of Vibrio / anaerogenic Aeromonas was observed in the intestines as fish grew and diets changed. The Vibrio /anaerogenic Aeromonas group was dominant in Lumbricillus rivalis used as an intermediate diet and the increased incidence of this group in fish intestines occurred after fish were fed this diet. The composite pellet used for ongrowing carried a high percentage of Gram positive micro-organisms and there was no relationship between the pellet microflora and that found in the fish intestines.     

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.     

Coupling of heart rate and locomotor activity in sole, Solea solea (L.), and bass, Dicentrarchus labrax (L.), in their natural environment by using ultrasonic telemetry

Field measurements of distance moved and heart rate in sole, Solea solea (L.) and bass, Dicentrarchus labrax (L.) using ultrasonic telemetry revealed two different strategies. Heart rate in the sole increases during activity, accurately reflecting fluctuation in metabolic rate and so can be used as a measure of metabolic rate in the field. In contrast, the relatively stable value of the heart rate in bass during the whole tracking period whatever the activity level suggests that in this species heart rate in the field cannot be associated with metabolic rate determination.     

Cross-shelf dispersion of Dover sole (Solea solea) eggs and larvae in Biscay Bay and recruitment to inshore nurseries

We studied the cross-shelf dispersion of Dover sole (Solea solea)eggs and larvae from the offshore spawning grounds to the coastalnurseries of Biscay Bay in 1987. Eggs and larvae were retainedover the spawning grounds from late February to early April,consistent with the limited movement of satellite-tracked Lagrangiandrifters at different depths in the water column. The distributionof the larvae coincided with maximum zooplankton abundance.In mid April, both sole larvae and drifters moved northwardin response to wind forcing but the advection rate of the larvaewas about one-third that of the drifters. No significant onshoreadvection of the pelagic stages was observed. No evidence wasfound for a behavioural selection of tidal currents by the pelagiclarvae that could lead to onshore transport Unless that behaviourdeveloped after settlement to the bottom, cross-shelf diffusionof the pelagic stages would represent the main avenue of transportto the coastal nursery grounds. This dispersion strategy wouldimply that the vast majority of sole larvae fail to recruitto the bays and estuaries and arc lost to the population.     

Seasonal distribution and duration of the planktonic stage of Dover sole, Solea solea, larvae in the Bay of Biscay: an hypothesis

The possibility of deriving a prediction about the effect of seasonal variations in the duration of the planktonic larval phase on the dispersal of larval Dover sole was investigated. During six cruises, from February to May 1992, the distribution of sole larvae was studied along a 100-km transect, from the offshore spawning grounds to the coastal nurseries of the Bay of Biscay (France). Samples ( n = 189) were collected with a suprabenthic sampler, and vertical profiles of water temperature and salinity were recorded simultaneously. Counts of otolith increments of larval stage 4b (onset of metamorphosis) were used to estimate the duration of the planktonic life. Duration of the larval phase decreases by about 15 days (37%) with water temperature increase (between 8° in February and 11.2° C in May). Sole larvae occur from the coastal area to 100 km offshore. Within the same cruise, no difference in the duration of the planktonic life was observed between the larvae caught in the onshore and the offshore area. In spite of seasonal differences in abundance, the extent and the shape of the larval distributions during the period of study suggest that the seasonal variations in the duration of the planktonic life did not affect the larval distribution.     

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.     

Malnutrition may affect common sole (Solea solea L.) growth, pigmentation and stress response: molecular, biochemical and histological implications

In the last decades there have been several evidences that traditionally used live preys like rotifers and Artemia salina have nutritional deficiencies that result in a general decrease of fish health, causing anomalies in the development, in growth and in pigmentation. In this study a partial of total replacement of traditional live preys with preserved copepods that represent the natural food of the larvae was evaluated during Solea solea culture. In this study a positive effect of co-feeding preserved copepods in sole larviculture was observed since larvae fed this diet growth and survived better, showed a better tolerance to captive conditions and had a better response to the final thermal/density stress-test with respect to larvae fed a traditional diet. Morphometric data were fully supported by molecular and biochemical ones. Moreover, liver histological investigations, revealed that the inclusion of preserved copepods in the larval diet was able to improve lipid assimilation. In conclusion, preserved copepods may be considered a suitable food for sole when used as a supplement to the traditional diet based on rotifers and Artemia nauplii.     

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.     

Thermal Preference of Juvenile Dover Sole (Solea solea) in Relation to Thermal Acclimation and Optimal Growth Temperature

Dover sole (Solea solea) is an obligate ectotherm with a natural thermal habitat ranging from approximately 5 to 27°C. Thermal optima for growth lie in the range of 20 to 25°C. More precise information on thermal optima for growth is needed for cost-effective Dover sole aquaculture. The main objective of this study was to determine the optimal growth temperature of juvenile Dover sole (Solea solea) and in addition to test the hypothesis that the final preferendum equals the optimal growth temperature. Temperature preference was measured in a circular preference chamber for Dover sole acclimated to 18, 22 and 28°C. Optimal growth temperature was measured by rearing Dover sole at 19, 22, 25 and 28°C. The optimal growth temperature resulting from this growth experiment was 22.7°C for Dover sole with a size between 30 to 50 g. The temperature preferred by juvenile Dover sole increases with acclimation temperature and exceeds the optimal temperature for growth. A final preferendum could not be detected. Although a confounding effect of behavioural fever on temperature preference could not be entirely excluded, thermal preference and thermal optima for physiological processes seem to be unrelated in Dover sole.