The ultrastructure of plaice (Pleuronectes platessa) leucocytes

The leucocytes of plaice were examined and, at a morphological level, in addition to their response to the injection of carbon particles, they could be divided into four main types. Unlike previous reports, monocytes were seen. The neutrophil granules resembled the third granule type described in mammalian neutrophils. Monocytes and thrombocytes were the only cells to take up appreciable amounts of the carbon.     

Otolith microstructure indicating growth and mortality among plaice, Pleuronectes platessa L., post-larval sub-cohorts

Growth and mortality of post-metamorphosed plaice were studied by means of daily increments in the sagittal otoliths. The Gompertz model was the best fit to length-at-age data and there were no significant differences between length-at-age and back-calculated lengths. The microstructure pattern of the otoliths at metamorphosis was also used to estimate hatching and settlement distributions. Differential growth and mortality occurred among sub-cohorts; growth rates and mortality were higher in fish that settled earlier. In 1986, the best survival was for a sub-cohort settling in late May to early June. In contrast, in the warmer season of 1987, survival was highest for the second and third sub-cohorts settling in late April and mid May.     

Temperature and somitogenesis in embryos of the plaice (Pleuronectes platessa)

The rate of somitogenesis was observed in plaice embryos reared at 5 and 12°C. Somite formation occurred relatively later in development at 12 than at 5°C. At any given stage of development 5°C plaice embryos had significantly more somites than embryos reared at 12°C.     

Stress and water balance in the plaice Pleuronectes platessa

Summary Drinking and branchial water permeability have been measured in plaice, and the effect of handling stress on these and on water balance is reported. Stress markedly disturbs water balance, with a weight loss of 1.6% over 7 h, and a recovery period exceeding 19 h. Depression of the normal rate of ingestion accounts for about 14% of this imbalance. Stress-induced urination is not a significant factor. Branchial diffusional water permeability is more than trebled in response to handling, but a measure of accommodation is seen with repeated handling. The ratio of osmotic to diffusional branchial water permeability is about 2.5 and is not appreciably affected by stress. Oxgen uptake is enhanced in response to stress, and this is discussed in relation to the effects of stress on water balance.     

Leucocytes and related cells in the plaice Pleuronectes platessa

The leucocytes and related cells of the blood of plaice were examined morphologically and their various functions assessed using a number of procedures to identify phagocytosis histochemical reactions and antibody responses. Four morphologically different types of thrombocytes were identified in addition to lymphocytes, plasma cells, monocytes, macrophages and one type of granulocyte which histochemically resembled the mammalian neutrophil. The evolution and development of the cells was also investigated and the various stages described.     

Genetic analysis of enzyme polymorphisms in plaice (Pleuronectes platessa).

Genetic analysis was performed on five enzyme systems (G3PDH; GPI-A; GPI-B; PGM; MDH-A) in plaice (Pleuronectes platessa) collected in spawning condition from the North Sea. Conventional crosses, induced gynogenesis and induced triploidy were performed. The data conclusively demonstrated the inheritance of isozymes by co-dominant alleles at individual loci for each system. No linkage was observed but tests did not include MDH nor the possibility of linkage between G3PDH and GPI-A. Some anomalous segregation ratios were observed, particularly a deficiency of heterozygotes for GPI-A, but the data were largely in conformity with Mendelian expectations. At the PGM locus, five independent anomalous individuals were scored and interpreted as mutations with a mutation rate of 1.1 X 10(-3) per gamete. Recombination with the centromere was assessed and induced triploidy and cross-over values of 41 per cent for PGM, 19 per cent for MDH-A and 9 per cent for GPI-B were derived on the assumption of complete interference. Amongst the parent fish, genotypic and phenotypic frequencies were largely consistent with the expectations of the Hardy-Weinberg Law, and allelic frequencies were not significantly different between year of collection or location of collection ground.     

Monoaminergic nerves in the skin of plaice Pleuronectes platessa (L.)

1. The fluorescent histochemical technique of Falck and Hillarp was applied to plaice skin. The presence of monoaminergic nerve terminals, containing predominantly stores of adrenaline, forming a plexus in and around the melanophore layer was demonstrated. 2. Such stores were enriched by noradrenaline in the presence of monoamine oxidase inhibitor, unaffected by spinal section, depleted by spinal nerve section or ligatures and abolished by reserpine. 3. The observations support the view that teleost sympathetic melanophore aggregating nerves are truly adrenergic.     

Studies on the skin of plaice (Pleuronectes platessa L.)

A histological, histochemical and ultrastructural examination of the skin of wild and cultured plaice was carried out, using fish from each year class from 0+ to 4+. The skin was shown to be similar in general structure to that of other teleosts but a previously undescribed cell, designated the Eosinophilic Granular Cell, a dendritic secretory cell found throughout the basal layers of the epidermis, is described. It was fixed only by formalin or dichromate, and contained numerous acidophilic granules. Melanin-bearing macrophages were observed migrating through the epithelium, but no DOPA or tyrosinase positive cells were observed by the methods used. Mast cells were very common in the dermis but were only demonstrable by special techniques. The melanophore and guano-phore systems are described and although no melanophores or melanocytes were found in the unpigmented areas of partially pigmented hatchery-reared fish, the integrity of the guanophore system was complete in such fish.     

A specific ringer solution for the plaice (Pleuronectes platessa L.)

Following analysis of the serum of the blood of the plaice ( Pleuronectes platessa L.), a Ringer solution specific for this fish has been devised and tested. It has proved a satisfactory physiological saline for use in electrophysiological experiments and in the preparative procedures for electron microscopy.     

Isolation of plaice (Pleuronectes platessa) alpha1-microglobulin: conservation of structure and chromophore

A cDNA coding for plaice (Pleuronectes platessa) alpha1-microglobulin (Leaver et al., 1994, Comp. Biochem. Physiol. 108B, 275-281) was expressed and purified from baculovirus-infected insect cells. Specific monoclonal antibodies were then prepared and used to isolate the protein from plaice liver and serum. Mature 28.5 kDa alpha1-microglobulin was found in both liver and serum. The protein consisted of an 184 amino acid peptide with a complex N-glycan in position Asn123, one intrachain disulfide bridge and a yellow-brown chromophore. Physicochemical characterization indicated a globular shape with a frictional ratio of 1.37, electrophoretic charge-heterogeneity and antiparallel beta-sheet structure. A smaller, incompletely glycosylated, yellow-brown alpha1-microglobulin as well as a 45 kDa precursor protein were also found in liver. The chromophore was found to be linked to alpha1-microglobulin intracellularly. Recombinant plaice alpha1-microglobulin isolated from insect cells had the same N-terminal sequence, globular shape and yellow-brown color as mature alpha1-microglobulin, but carried a smaller, fucosylated, non-sialylated N-glycan in the Asn123 position. The concentration of alpha1-microglobulin in plaice serum was 20 mg/l and it was found both as a 28.5 kDa component and as high molecular weight components. Thus, the size, shape, charge and color of plaice alpha1-microglobulin were similar to mammalian alpha1-microglobulin, indicating a high degree of structural conservation between fish and human alpha1-microglobulin. The monoclonal antibodies against plaice alpha1-microglobulin cross-reacted with human alpha1-microglobulin, emphasizing the structural similarity.     

The immunohistochemical localization of lysozyme in plaice (Pleuronectes platessa L.) tissues

The location of lysozyme in fresh plaice ( Pleuronectes platessa L.) tissues was studied using an immunofluorescent technique. An antiserum to a homogeneous sample of plaice serum lysozyme was prepared in rabbits and was shown to be monospecific by immunodiffusion and inhibition studies. This preparation, used in conjunction with fluorescent labelled sheep anti-rabbit immunoglobulin, demonstrated lysozyme in plaice neutrophils, peritoneal macrophages, gill cartilage and epithelium, spleen, kidney, skin and mucus. The distribution of lysozyme in the skin and secreted mucus was affected by the method of killing the fish.     

Aspects of leucocyte migration in the plaice, Pleuronectes platessa L.

Histological studies on plaice tissues revealed mononuclear phagocytes emigrating through capillary endothelium in response to bloodborne foreign erythrocytes, with a >50% increase in circulating leucocytes within 2 h. Despite this rapid influx of leucocytes, cellular accumulation during peritoneal inflammatory responses was significantly slower than in mammals. In vitro studies with chemotaxis chambers revealed that random leucocyte migration was enhanced in the presence of endogenous chemostimulatory substances (inflammatory exudate fluid and endotoxin-activated plaice serum) although directional migration was not demonstrated. It is suggested that, compared with mammals, the slower accumulation of teleostean leucocytes at sites of injury is not due to a locomotory defect but possibly results from lower levels of endogenous chemoattractants being generated.     

Effect of opsonization on oxidative metabolism of plaice (Pleuronectes platessa L.) neutrophils

The effect of serum opsonization on Vibrio alginolyticus (heat-killed)-stimulated chemiluminescence (CL) by plaice kidney- and peritoneal exudate-derived neutrophils was investigated. Peritoneal neutrophils only recognized heat-labile and kidney neutrophils only heat-stable opsonic activity in normal serum. Specific antibody did not show opsonic activity nor any synergism with the normal serum opsonins for either neutrophil population. Evidence was found for the production, by plaice neutrophils, of H2O2, O2-, OH. and two or more, as yet unidentified, reactive oxygen species (ROS).     

Cutaneous oxygen uptake and its relation to skin blood perfusion and ambient salinity in the plaice, Pleuronectes platessa

Oxygen uptake across plaice skin was unaffected by temporary arrest of skin blood flow. This indicates that oxygen taken up across the skin is consumed by the skin itself. Weight specific rate of O2-consumption of skin is estimated to be 1.7-1.9 times that of the entire fish. Total resting O2-consumption increased from 0.43 to 0.58 mg X kg-1 X min-1 when salinity was raised from 8.5 to 25%. The relative increase in O2-uptake across the skin following an increase in salinity was smaller than the increase in total O2-uptake. This is taken to indicate that the high O2-consumption of skin is not specifically related to an osmoregulatory function of the skin.     

Year-class strength regulation in plaice (Pleuronectes platessa L.) on the Swedish west coast

Year-class strength of plaice (Pleuronectes platessa) has been studied over periods of 10 and 35 years, respectively, in two shallow sandy areas on the Swedish west coast. In one area, Gullmar Bay (N 58 ° 19 – W 11 ° 33), 0-group plaice were sampled quantitatively with a drop trap at 0–0.7 m depth and densities between 0.2 and 3.8 ind./m² were recorded in early summer. In the other area, Laholm Bay (N 56 ° 30 – W 12 ° 55), 0-group plaice were sampled semi-quantitatively in August with young-fish trawl at 1.5 m depths. Densities between 0.001 and 0.28 ind./m² were assessed.The effects of temperature and wind (in the winter and early spring) and predation (in early summer), on the recruitment of 0-group plaice were investigated. In Gullmar Bay high recruitment occurred after severe winters and in years when on-shore winds dominated during spring. No such correlations were found in Laholm Bay. In Gullmar Bay a significant inverse relationship was found between the density of O-group plaice in early summer and the biomass of brown shrimp (Crangon crangon) and the shore crab (Carcinus maenas), the main predators in the nursery area.The importance of physical and biological factors regulating recruitment in plaice are discussed.