Sexual dimorphism in scales of marbled flounder Pseudopleuronectes yokohamae (Pleuronectiformes: Pleuronectidae), with comments on the relevance to their spawning behaviour

Variation of scales on the blind side of Pseudopleuronectes yokohamae in relation to sex, maturity and body size was examined. Immature males often have cycloid scales, while mature males have mostly ctenoid scales. Large females also often have ctenoid scales (but with fewer spines compared with males), and small females have mostly cycloid scales. The number of spines (ctenii) on the blind‐side scale increases with body size in both sexes, indicating an ontogenetic change in scale morphology. As P. yokohamae spawn demersal eggs with males positioning themselves above the females on the ocular side, it is hypothesized that ctenoid scales on the blind side in mature males function for maintaining contact with females during spawning.     

Increased 5-Hydroxytryptamine and Norepinephrine Release from Rat Brain Slices by the Red Sea Flatfish

The effect of the Red Sea flatfish toxin pardaxin was examined on K+-evoked and on basal release of either [3H]norepinephrine or [3H]5-hydroxytryptamine from preloaded rat cortical slices. The K+-induced release of the neurotransmitters was stimulated in a dose-related manner at concentrations ranging from 0.5 to 4 micrograms/ml. Basal release of the two transmitters was elevated to a lesser extent. Although the stimulation of evoked release was approximately equivalent for the two neurotransmitters, the response to 5-hydroxytryptamine was reversible whereas that of norepinephrine was not washed by 20 min of superfusion. The mechanisms involved in producing these actions of pardaxin are not known; however, they may be mediated by changes in electrolyte fluxes across the neuronal membranes.     

Diel variability in catch rate of juvenile flatfish on two small nursery grounds (Port Erin Bay, Isle of Man and Porto Pirn Bay, Faial, Azores)

Variation in beach seine catches was examined in two juvenile flatfish populations (Port Erin, Isle of Man and Porto Pirn, Azores) to determine the importance of diel cycles while controlling for tidal rhythmicity. At Port Erin sampling was undertaken at each low water on consecutive days over a 2-week period in May/June and September 1991. There was no periodicity in the catches of plaice ( Pleuronectes platessa ) in May/June, but in September catches were higher at night. Other flatfish species ( Limanda limanda, Pleuronectes flesus, Scophthalmus maximus and S. rhombus ) sampled at Port Erin were nocturnal. At Porto Pirn, Azores, fish were sampled over 24 h each month from July 1989 to June 1990 and at each low water over a 2-week period in July 1991. The only flatfish species present was Bothuspodas , which had a diurnal pattern in catches over a 1-year period. Sampling at low water in July gave high catches at both midnight and midday.     

High dietary arachidonic acid levels affect the process of eye migration and head shape in pseudoalbino Senegalese sole Solea senegalensis early juveniles

The effect of high dietary levels of arachidonic acid (ARA) on the eye migration and cranial bone remodelling processes in Senegalese sole Solea senegalensis early juveniles (age: 50 days post hatch) was evaluated by means of geometric morphometric analysis and alizarin red staining of cranial skeletal elements. The incidence of normally pigmented fish fed the control diet was 99·1 ± 0·3% (mean ± s.e .), whereas it was only 18·7 ± 7·5% for those fed high levels of ARA (ARA‐H). The frequency of cranial deformities was significantly higher in fish fed ARA‐H (95·1 ± 1·5%) than in those fed the control diet (1·9 ± 1·9%). Cranial deformities were significantly and negatively correlated with the incidence of normally pigmented animals (r² = ?0·88, P < 0·001, n = 16). Thus, fish displaying pigmentary disorders differed in the position of their eyes with regard to the vertebral column and mouth axes, and by the interocular distance and head height, which were shorter than in fish not displaying pigmentary disorders. In addition to changes in the positioning of both eyes, pseudoalbino fish showed some ARA‐induced osteological differences for some of the skeletal elements from the splanchnocranium (e.g. right premaxillary, dentary, angular, lacrimal, ceratohyal and branchiostegal rays) and neurocranium (e.g. sphenotic, left lateral ethmoid and left frontal) by comparison to normally pigmented specimens. Pseudoalbino fish also had teeth in both lower and upper jaws. This is the first study in Pleuronectiformes that describes impaired metamorphic relocation of the ocular side eye, the right eye in the case of S. senegalensis, whereas the left eye migrated into the ocular side almost normally.     

Vertical Distribution and Feeding Activity of Metamorphosing Sole, Solea Solea, Before Immigration to the Bay of Vilaine Nursery (Northern Bay of Biscay, France)

To evaluate the impact of metamorphosis on the vertical distribution and feeding activity of sole, Solea solea, larvae passing from offshore spawning grounds to the Bay of Vilaine, sampling series at fixed stations were carried out in April 1991 and April 1993 at depths from 50 to 30 m. Comparisons between plankton and bottom samplin series indicated differences in vertical distribution of larvae in pre-metamorphic and metamorphic steps. Metamorphosing larvae displayed a tendency to concentrate in the lower part of the water column, mainly during the day. Gut contents, analysed for prey identification, fullness index and carbon content, indicated that metamorphosing larvae fed mostly on plankton. Variations in fullness index were observed not only during the day, but also depended on tide and wind-induced mixing conditions. Larvae sampled in mixed spring-tide waters had highly variable carbon estimates, resulting in unclear diel activity. More larvae fed actively at neap-tide, which allowed the observation of a diurnal feeding activity through hourly changes in carbon estimates. It is concluded that immigrating sole were not yet able to settle but prepared themselves for demersal life (i) without undergoing starvation and (ii) by modifying the patterns of vertical distributions. The presence of a larval swimbladder suggests they can adjust their vertical movements, depending on tidal cycles, which could in turn favour coastal accumulation of metamorphosing larvae and pulses of new settlers entering the nursery grounds.     

Molecular systematics of the Atlanto-Mediterranean Solea species

Within the genus Solea , four sister lineages have been evolved that actually correspond to the species S. vulgaris, S. senegalensis, S. kleini and S. lascaris . The existence of S. aegyptiaca and S. impar is not supported and these species can be synonymized under S. vulgaris and S. lascaris , respectively. This pattern of taxonomy agrees fully with that proposed by Ben-Tuvia (1990; Journal of Fish Biology 36, 947–960) based on morphological features. In addition, mtDNA data contradict the widely accepted relatedness between S. kleini and S. lascaris based on the shared enlarged forenostril on the blind side. A sample of soles clearly related to S. senegalensis was caught in the Gulf of Taranto (Ionian Sea), representing the most western finding of this species in the Mediterranean Sea.     

Geographic variation in the maturity and growth schedules of English sole along the U.S. west coast

Logistic regression analyses showed that the maturity v. length relationship for female English sole Pleuronectes vetulus varied significantly among sampling locations from California to British Columbia in June–September. Stepwise analyses found that latitude, bottom gradient, bottom temperature and sediment type were all significant factors. Regression analyses of age at length from subsamples indicated that latitude, maturity and bottom sediment had significant effects on growth. Data from the aged subsamples showed significant differences among age classes in the length v. maturity relationship with older fish attaining maturity at smaller sizes than younger fish. On a coast wide basis the length and age at 50% maturity were c. 230 mm and 4·7 years respectively. Growth rate and length at 50% maturity have decreased substantially relative to observations from the 1950s, but age at 50% maturity has increased.     

Feeding ecology and growth of O-group flatfish (sole, dab and plaice) on a nursery ground (Southern Bight of the North Sea)

The food composition of O-group sole Solea solea , dab Limanda limanda and plaice Pleuronectes platessa on a nursery ground at Gravelines, France, included 17–25 taxa. Sole (new settlers) fed mainly on harpacticoid copepods and when 50 mm in size, on polychaetes (Terebellidae). Dab (<40 mm) consumed mainly polychaetes (Magelonidae and Spionidae), and later amphipods, polychaetes (Spionidae) and Hydrozoa. O-group plaice diet was dominated by polychaetes (Terebellidae), crustaceans and molluscs at all sizes. O-group sole, dab and plaice did not compete for food resources, each species being specialized in different prey items. Growth rates during May-July 1998 varied between 0·5 and 0·67 mm day⁻¹ for sole, 0·12 and 0·24 mm day⁻¹ for dab and 0·55 and 0·81 mm day⁻¹ for plaice. For sole and plaice, these estimates were similar to those recorded in other nurseries and also close to the maximal growth predicted by experimental models. This suggests that their growth was not limited by food during the first summer of life.     

Hepatic Tumors in Flatfish from Sivuch'ya Bight (Peter the Great Bay, Sea of Japan)

The livers of six flatfish species from Sivuch'ya Bight were examined histologically for the presence of neoplastic lesions. Out of 120 fish studied, hepatic tumors were found in two individuals: the black plaice Pleuronectes obscurusand the longsnout flounderPleuronectes punctatissimus.Based on presence of tissue and cellular atypism, tumor pearls surrounded by squamous cells, and absence of mucous secretion, the neoplasm in P. punctatissimuswas classified as squamous cell carcinoma. Abnormal growth of fibrous stroma suggests a scirrhous variant of carcinoma. Tumor in P. obscuruswas classified as a hepatocellular adenoma. This is the first information on liver tumors in flatfishes of Sivuch'ya Bight.