The karyotype of the dab (Limanda limanda L.)

In the dab ( Limanda limanda L.), the diploid number is 46 and the karyotype consists of 23 pairs of chromosomes, all of which are telocentric or subtelocentric, so that the total number of chromosome arms is 46 (AN-46).     

Seasonal changes in the common dab, Limanda limanda (L.) in Isle of Man Waters

Otolith accretion was greatest in summer when opaque bands were laid down and slowest in winter when hyaline rings were formed. Food intake was minimal in winter and maximal in summer. Liver weight was high in summer and winter and low in spring after spawning. Growth in length was higher in summer than winter. Gonad weight was greatest in winter for both sexes. Spawning occurred from February to April. After spawning males recovered earlier than females and testes ripened earlier than the ovaries. From winter to summer, the sea temperature increased from 7.5–13.0°C; the day length from 7–17h; and the salinity varied from 34.07−34.36%.     

Gastric emptying and the return of appetite in juvenile turbot, Scophthalmus maximus L., fed on artificial diets

Gastric emptying time in Scophthalmus maximus , when fed friable artificial pellets based on fishmeal, is composed of two phases:
(a) a delay time (t_d) during which the meal forms a bolus and which shortens with temperature, and
(b) an emptying phase (duration t_end ) which varies with meal size ( S ), body weight ( W ) and temperature (71 according to:
(where t _end is in h, S is in g, W is in g and T is °C). During the emptying phase, stomach contents decrease curvilinearly according to:
(where S_t , & S_o is in g and t is in h) in which the instantaneous digestion rate, K , varies with fish weight and temperature as:
Food pellets were prepared which remained separate and did not form a bolus in the stomach; K increased if a given meal size was subdivided to increase surface area. If meal size was increased by ingestion of identical pellets, K decreased. After a satiation meal, appetite in young turbot returns in direct relation to the degree of stomach emptiness. When food is regularly available, young turbot feed steadily at a rate which maintains their stomachs at c. 85% maximum fullness. When trained to use demand feeders, the fish interact as a group to feed rhythmically, but feeding rate falls 33% to only two-thirds of the previous rate since stomach fullness, and hence digestion rate (g h⁻¹), is maintained at a lower level. Reduction in dietary energy density below 1 kCal g⁻¹ increases gastric emptying rate and the turbot demonstrate partial compensation by increasing food intake. On energy-rich diets, protein nitrogen and energy assimilation efficiencies remain high (97 5% and 91% respectively) irrespective of feeding rate and frequency.     

The reproductive biology of the dab Limanda limanda (L.) in the North Sea: Seasonal changes in the testis

Spermatogenesis in the dab is described in five easily identifiable stages: spermatogonium (Stage I), primary spermatocyte (II), secondary spermatocyte (III), spermatid (IV), and spermatozoon (V). The annual reproductive cycle in male dab may be divided into four morphologically and histologically distinct periods: prespawning (September-November), spawning (December-March), postspawning (April-May) and resting (June-August) period.     

The reproductive biology of the dab Limanda limanda (L.) in the North Sea: Seasonal changes in the ovary

Oogenesis in the dab is described in six easily identifiable stages: oogonium (Stage I), primary oocyte (II), primary vitellogenesis (III), secondary vitellogenesis (IV), tertiary vitellogenesis (V) and hyaline oocyte (VI). The annual reproductive cycle in female dab may be divided into four morphologically and histologically distinct periods: prespawning (October–January), spawning (February–April), postspawning (May–June) and resting (July–September) period.     

Maximum daily ration and the pattern of food consumption in haddock, Melanogrammus aeglefinus (L.), and dab, Limanda limanda (L.)

Food intake was measured under conditions of continuous food availability for haddock, Melanogrammus aeglefinus (L.), and dab, Limanda limanda (L.). Haddock consumed approximately 75% of all food during the day, with a peak of feeding at dusk and an inferred peak at dawn; peaks of feeding were associated with larger meals. By contrast, dabs were mainly night-time feeders with daily consumption rates that were approximately 40% lower than those shown by haddock. Comparison of haddock maximum daily ration with published estimates of consumption in the wild indicate that wild haddock feed at between 15 and 22% of their maximum capacity. Using published data on gastric evacuation, the relationship between meal size and stomach residuum was investigated. There was no detectable relationship between these two variables.     

Development of 30 microsatellite markers for dab (Limanda limanda L.): a key UK marine biomonitoring species

Dab (Limanda limanda) are the principal target fish species in offshore biomonitoring programmes in the UK; however, detailed knowledge of genetic structure and connectivity among sampling locations is unavailable. Here, the isolation and characterization of 30 polymorphic microsatellite loci for dab is described. The number of alleles per locus ranged from 2 to 42, with observed heterozygosities ranging from 0.089 to 1. These loci will enable high resolution of genetic population structure and dynamics of dab around the British Isles.     

The feeding ecology of Pleuronectes platessa L., Limanda limanda (L.) and Scophthalmus rhombus (L.) in Carmarthen Bay, South Wales, U.K.

To assess the feeding habits of plaice, Pleuronectes platessa L., and dab, Limanda limanda (L.), within Carmarthen Bay, three sampling techniques were used: benthic trawling and surf-zone push-netting were undertaken during the feeding season for the gut contents of plaice and dab (age groups 0-IV) and of 0-group brill, Scophthalmus rhombus , to be analysed in detail, and a benthic macro-fauna grab survey covered the trawled ground to assess the distribution of food species in relation to gut contents. Plaice consumed commonly-occurring food species whereas dab took any available food. The main items were the same for both species, but secondary food preferences differed. Variations in gut contents within species, for the same sized fish, chiefly resulted from the spatial distribution of fish and not seasonal variations in the benthic macro-fauna. The length and not the age of fish primarily determined the selection of food organisms.     

Ethoxyresorufin O-deethylase (EROD) activity in the liver of dab (Limanda limanda L.) and flounder (Platichthys flesus L.) from the German Bight. EROD expression and tissue contamination

Ethoxyresorufin O-deethylase (EROD) activity was measured in the liver of dab (Limanda limanda) and flounder (Platichthys flesus) from the German Bight (southern North Sea) and compared with muscle and liver polychlorinated biphenyl (PCB) concentrations in an attempt to relate EROD activity to PCB body burden. In none of the different datasets (species-, tissue- or matrix-dependent) was a significant (P<0.05) correlation between PCB tissue contamination and EROD activity found. Yet EROD activity was significantly correlated with polycyclic aromatic hydrocarbons (PAH) levels (phenanthrene, fluoranthene, pyrene) in muscle tissue, indicating a possible dependence of EROD expression on other ubiquitous organic contaminants, thus making it a suitable biomarker for general pollution. Received: 14 April 1999 / Received in revised form: 10 July 1999 / Accepted: 15 July 1999     

Plasma glucose and plasma fatty acid levels of Limanda limanda (L.) in relation to season, stress, glucose loads and nutritional state

The effects of season, stress, glucose loads and nutritional state on the plasma glucose (PG) and plasma fatty acids (PFA) of Limanda limanda were examined. Plasma glucose levels showed no seasonal variation while PFA exhibited two peaks during May to August, and in December respectively. These peaks may be associated with resorption of gonadal material after spawning and the mobilization of lipid reserves for vitellogenesis. Limanda showed a hyperglycaemic response to a brief aerial emersion, followed by a hypoglycaemic condition. Infusion of a glucose load and the ingestion of a satiation meal of Mytilus edulis tissue led to a reciprocal rise and fall of PG and PFA. Short-term food deprivation had no effect upon PG although PFA rose significantly.     

Assessment of some innate immune responses in dab (Limanda limanda L.) from the North Sea as part of an integrated biological effects monitoring

The marine flatfish dab (Limanda limanda), which lives in direct contact with contaminated sediments, is frequently used as a sentinel species in international monitoring programmes on the biological effects of contaminants. In this study, immune responses were recorded as indicators of sublethal chronic effects of contaminants, in addition to measurement of the induction of mono-oxygenase ethoxyresorufin O-deethylase (EROD) in liver cells, the inhibition of acetylcholin esterase (AChE) in muscle and a quantification of grossly visible diseases and parasites. In total, 336 dab were analysed from five sampling areas in the North Sea, including the German Bight, the Dogger Bank, the Firth of Forth, and two locations close to oil and gas platforms (Ekofisk and Danfield). When considering plasma lysozyme levels, pinocytosis and respiratory burst activity of head kidney leucocytes, a clear gradient could be observed with decreased levels in individuals collected from the Firth of Forth and locations near the oil or gas platforms compared with dab from the Dogger Bank or the German Bight. Individuals with induced EROD activity displayed reduced lysozyme and respiratory burst activities. Lysozyme levels were also reduced in dab with lymphocystis or with nematodes. The data obtained indicate that the assessment of innate immune parameters in a monitoring programme provides supplementary information about immunomodulatory effects associated with the exposure of fish to contaminants. In particular, concentrations of plasma lysozyme, which can be analysed in an easy and inexpensive assay, are considered to be an appropriate parameter for use in a battery of other bioindicators. Communicated by H. von Westernhagen and A. Diamant     

Gastric emptying in Scyliorhinus canicula (L.): a comparison of surface-dependent and non-surface dependent models

The usefulness of both surface-dependent and non-surface-dependent models for describing the gastric emptying process in Scyliorhinus canicula (L.) was examined. In most cases the surface-dependent models produced better fits than did the non-surface-dependent models. The exponential model (non-surface-dependent) only adequately described gastric evacuation in the case of small prey items with thin exoskeletons. On the other hand, the exponential model was clearly better than the linear model in all cases. Prey size had little effect on digestion rate. However, the number of prey items ingested was an important factor influencing digestion.     

Some observations on the seasonal distribution of dab,Limanda limanda, in the southern North Sea

The seasonal changes in the population structure of dab were observed in intervals of four to six weeks from January 1993 to November 1994 at a fixed station northwest of Helgoland. The sex distribution was characterized by a reduced number of males during autumn and winter. In the autumn of both years, an immigration of large females was evident. During long periods in spring and summer, the population structure remained relatively constant. The observations indicate that dab in the Helgoland region carry out a seasonal migration between coastal waters and the sampling area. Seasonal changes of the population structure occurred at a relatively slow rate.     

Gastric emptying in cod, Gadus morhua L.: emptying and retention of indigestible solids

Particles 2 mm or smaller may be passed relatively easily through the pylorus of the cod, Gadus morhua L., but, under some conditions, 5 mm particles are held in the stomach for prolonged periods. The emptying of indigestible particles appears to be impaired by the consumption of additional meals, and prolonged retention of these particles may occur in fish fed multiple meals. The findings agree in general with those reported for mammals and the results are discussed in relation to mechanisms thought to control gastric motor activity patterns.     

Seasonal changes in frequency of diseases in dab,Limanda limanda,from the southern North Sea

Infestation rates of flatfishLimanda limanda from the southern North Sea (German Bight) were investigated in 1981 and 1982. At three stations, including a dumping area of acid-iron wastes northwest of Helgoland, dabs were examined for the occurrence of lymphocystis and epidermal papillomas. Marked seasonal changes of infestation rates were observed with maxima of diseased fish in March and May (epidermal papillomas 2 % in 1981, 4.1 % in 1982; lymphocystis 7.5 % in 1981, 17.2 % in 1982). Infestation minima were found from June to October. Differences in incidence rates were observed between stations in winter and spring, but not in summer. Both diseases turned out to be size-dependent. Seasonality of the two diseases is discussed in relation to spawning cycle and water quality, including pollution.     

A comparison of food capture and ingestion in juveniles of two flatfish species, Pleuronectes platessa and Limanda limanda (Teleostei: Pleuronectiformes)

Juvenile plaice, Pleuronectes platessa ( n =6, 151–197 mm SL) and dab Limanda limanda ( n =6, 119–180.5 mm SL) feeding on pieces of mussel flesh were studied by high-speed (200 fields s⁻¹) videophotography at 11) C. Prey capture cycles (involving jaw protrusion and opercular expansion) were described in both species. The capture cycle was followed by at least one cycle (similar to the capture cycle in all respects except food intake) which is believed to transport food to the oesophagus. The transport cycle (or cycles) was followed by a species-specific number of normal respiratory cycles (7 or 8 in plaice, 11 or 12 in dab) and a final single cycle when food debris was violently ejected from the opercular cavity. The respiratory cycles and ejection cycle cleansed the orobranchial/opercular cavities and gills. Differences between the species were relatively minor, but plaice captured and transported food more quickly than dab.