Copper metabolism in the plaice, Pleuronectes platessa (L.)

Copper metabolism in a teleost, the plaice, Pleuronectes platessa (L.) from a natural environment has been studied. Distribution in the various tissues of the metal and of five key copper-dependent enzymes: ceruloplasmin EC 1.16.3.1; Superoxide dismutase EC 1.15.11; tryptophan oxygenase EC 1.13.1.12; cytochrome oxidase EC 1.9.3.1 and monoamine oxidase EC 1.4.3.4 have been determined. The copper distribution was found to be similar to that in mammals with the greatest concentrations in the brain and heart. Distribution of the copper enzymes is also similar to that found in mammals. A preliminary characterization of the copper enzymes showed that plaice cytochrome oxidase has a pH maximum 2 pH units more alkaline than the mammalian enzyme and that plaice tryptophan oxygenase is more sensitive to heat denaturation than the mammalian enzyme. The present data form a base-line against which studies on factors affecting the copper metabolism in a teleost can be assessed.     

A quantitative description of the behaviour of wild juvenile plaice (Pleuronectes platessa L.)

The behaviour of young plaice (Pleuronectes platessa L.) as they migrate up and down sandy beaches with the tide is described. Their behaviour during this migration consists mainly of swimming and feeding interspersed with rarer behavioural acts. Over short periods swimming behaviour can be described by a random model in which the probability of a swim occurring remains constant. This probability varies markedly, however, from hour to hour. Two types of swimming movement are recognized: one of very short duration represents searching for food and the other, longer, category serves to transport the fish up and down the shore. Variations in the feeding rate and in the frequency, duration, and direction of swimming movements over the tidal cycle are described and related to the changing physical and biological conditions that the fish experience during their intertidal movements.     

The accumulation of organic mercury from sea water by the plaice, Pleuronectes platessa L

The accumulation of organic mercury from sea water by plaice eggs, larvae and adult fish has been studied using CH₃²⁰³HgCl as a tracer. The isotope was rapidly accumulated, the largest fraction being taken up by muscle tissue. High concentration factors were attained by many internal organs, particularly blood, spleen, and kidney. Longer biological half-times than previous estimates with ²⁰³HgCl₂ were obtained: the possible consequences of inorganic mercury accumulated from sea water being excreted at the rate for methylmercury have been calculated.     

Vulnerability of newly settled plaice (Pleuronectes platessa L.) to predation: effects of habitat structure and predator functional response

Plaice (Pleuronectes platessa) nursery grounds on the Swedish west coast have been subject to increasing cover of annual green macroalgae during recent years, with growth of algae starting at the time of plaice settlement in April to May. A laboratory experiment was performed to investigate how the vulnerability to predation of metamorphosing plaice was affected by the presence of filamentous algae. Predation by shrimps (Crangon crangon) on settling plaice larvae was higher on sand than among algae, whereas predation by crabs (Carcinus maenas) was unaffected by habitat type, suggesting a lower overall mortality of plaice in the vegetated habitat. When predators and prey were presented with a combination of the two habitats, predation by shrimps was as high as that in the sand treatment alone, whereas predation by crabs was lower than that in the two treatments with one habitat. Based on these results, an additional experiment was performed, investigating the functional response of shrimps to six densities of juvenile plaice in a sand habitat with alternative prey present. The proportional mortality of juvenile plaice (12-16 mm total length (TL)) was density-dependent and was best described by a type III (sigmoid) functional response of the predatory shrimps. The results suggested that the combined predation pressure from shrimps and crabs was lower among algae than on sand, but settling plaice and predatory shrimps chose the sand habitat. Plaice densities in the sigmoid part of the obtained functional response curve represented normal to high field densities of plaice on the Swedish west coast, suggesting that shrimp predation could have a stabilising effect on plaice recruitment. The formation of macroalgae mats could therefore lead to a concentration of plaice juveniles in the remaining sand habitat and increased mortality through density-dependent predation by shrimps.     

The accumulation and retention of 59Fe and 58Co by the plaice, Pleuronectes platessa L.

The accumulation of ⁵⁹Fe and ⁵⁸Co from water by plaice (Pleuronectes platessa L.) has been studied in tissues, and their levels of accumulation related to stable element concentrations. The retention of both radionuclides from labelled Nereis and labelled pellets has also been examined, and the loss of activity from intraperitoneal injections followed over a three-month-period. Biological half-times of the exchange with water have been calculated for many organs, although the rate of accumulation for some tissues could only be expressed as a linear function; however, for both radionuclides the direct accumulation from water resulted in concentration factors of less than 1 % of the values inferred from the stable element data. The relevance of such observations to heavy metal pollution at the higher trophic levels is discussed.     

Effect of temperature on the embryonic development of the plaice, Pleuronectes Platessa L. (teleostei)

In normalyears, eggs and prolarvae of the plaice (Pleuronectes platessa L.) in the southern North Sea develop within the temperature range 6.0–8.5 °C, although the water may at times be some degrees colder or warmer than this. The effect of temperature, t °C, on the embryonic development time, D days, has been investigated within the tolerated range 2.8–10.5 °C. Various models to express the observed curvilinear relationship between t and D have been considered, that giving the closest fit to the data being (t−t₀)(D−D₀) = k or $\text{D =}\text{k}\text{(t−t}{}_0\text{)+D}{}_0$. A method is given for the calculation of constants k, D₀, and t₀. The relationship may also be expressed by the equation D = a(t−t₀)^b where a and b are constants, but t₀ must in this case be found by iteration. At investigated temperatures in the range 4.1–10.5 °C the smallest eggs in a batch from a single source hatched first. Within the tolerated range, hatching prolarvae were substantially smaller at 10.5 °C than at the other temperatures. During the period of prolarval yolk utilization, growth is slower at the high temperatures, so that median temperatures of 6.5–8.0 °C are most efficient in terms of the relationship between growth in length and yolk utilization. Toward the end of the yolk-sac phase, the rate of yolk utilization declines unless a suitable external food source (e.g., Artemia nauplii) is provided.     

The settlement, distribution and movements of O-group plaice Pleuronectes platessa (L.) in Filey Bay, Yorkshire

The pelagic larval stages and the demersal O-group stage of plaice were sampled in the immediate vicinity of Filey Bay, Yorkshire (54°12'N, 00°16'W), using a modified Gulf V high-speed plankton sampler and beam trawls. The distribution and movements of these fish were studied from the time of first settlement in May through the period of metamorphosis and the O-group stage. It was found that the larvae settled in water deeper than 5 m and moved into shallow water following metamorphosis. This established a typical distribution of larger fish in shallower water than the smaller fish. When the fish grew over 40 mm they moved out again into deeper water which leads to a reversal of the lengthdepth distribution. Further movements during the winter months and of the I-group fish were studied by tagging. It was found that emigration from the nursery ground did not occur until the I-group stage.     

Some further studies on the accumulation and retention of 65Zn and 54Mn by the plaice, pleuronectes platessa L.

Some further studies on the accumulation and retention of ⁶⁴Zn and ⁵⁴Mn by plaice, Pleuronectes platessa L., have been made. Direct accumulation from water, by eggs and larvae, is insufficient to account for the concentrations of these metals in young fish. It appears, therefore, that, from the earliest stages, food constitutes the major pathway for accumulation. Stable element analyses of liver, muscle, and bone samples from fish of differing weights and ages show that their concentrations, in adult fish, remain fairly constant. On this basis it has previously been estimated that biological half-times of these metals via food should be shorter than those observed after accumulation from labelled water. Experiments following the loss of the isotopes from fish which had been fed labelled polychaete worms support this view.     

The accumulation of cadmium by the plaice, Pleuronectes platessa L. and the thornback ray, Raja clavata L.

The accumulation of cadmium (^115mCd) from both food and sea water by the plaice, Pleuronectes platessa L., and thornback ray, Raja clavata L., has been studied in relation to their measured cadmium concentrations. Plaice accumulated cadmium from sea water at a faster rate than rays, although the concentrations factors attained by both species as a result of such direct accumulation were very low. Both species retained cadmium from food and accumulated it in the liver, the rays relatively more than the plaice. From analyses of North Sea fish, some evidence was found for a positive linear relation between the concentrations of cadmium in plaice liver and age, but not weight, of the fish.     

Gill chamber ventilation and scaphognathite movements in Crangon crangon (L.)

Buried Crangon crangon (L.) produce, anterior to their gill chambers, an inhalant and exhalant channel in the substratum. The combined shape and disposition of the maxillipeds effects separation of the inhalatory and exhalatory streams, and this channelling allows the maintenance of a posteroanteriorly directed flow of water over the gills of buried animals.Impedance techniques have been used to obtain qualitative data on the movements of scaphognathites. Reversals were identified and seen to occur particularly during burying and at the onset of walking. Reversals begin by the anterior region of the scaphognathite missing a beat, and end with the middle and anterior regions pausing.Analyses of movement patterns of individual scaphognathites show that a beat comprises equally-effective depression levation phases, but the timing sequence of the movements differs slightly from that reported in Carcinus maenas.     

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.     

Symbiotic nitrogen-fixing root nodules of Lathyrus maritimus (L.) Bigel (beach pea) from Newfoundland shore lines with special reference to oleosomes (lipid bodies)

Lathyrus maritimus (L.) Bigel, commonly known as beach pea, grows along the shorelines of Newfoundland, Canada. Rhizobia have been isolated from the subterranean root nodules and the cultures were induced to nodulate seedlings raised in the laboratory. The nodules collected from the field were elongated and sometimes branched with proximal ends thickened. Histological characteristics revealed their indeterminate perennial form. Oleosomes (lipid bodies) were present in the nodule tissues. Morphometric analysis showed their presence in the nodule cortex cells throughout all developmental stages, but they were found in the infected cells only during the early stages of infection and symbiosis. It is suggested that oleosomes are utilized for membrane and rhizobial proliferation during establishment of symbiosis in the infected cells. The role of oleosomes in the cortical cells remains unclear.     

The effect of brown trout (Salmo Trutta L.) on stream invertebrate drift,with special reference to Gammarus pulex L.

The effect of brown trout (Salmo trutta L.) on invertebrate drift density was examined in three previously fish-free springbrooks. Drift density was studied during the day following the sequential introduction of: 1) empty cages, 2) cages containing trout, and 3) empty cages. Each period lasted three whole days, and drift density was measured at daytime and night-time every day. Control drift density was determined using empty cages in two similar springbrooks.Night-time drift density of large Gammarus pulex L. (>3.9 mg DW ind^–1) decreased compared to that of smaller size-groups following trout introduction, and was significantly lower (p<0.05) than the pre-introductory level after the trout had been removed again.The daytime drift density of large G. pulex remained unchanged, as did both daytime and night-time drift density of smaller size-groups of G. pulex, and the other taxa investigated (Leuctra hippopus (Kempny), Leuctra nigra (Olivier), Amphimura sp., Nemoura flexuosa Aubert, and Baetis rhodani (Pict.)). No significant changes in drift density were observed in two control springbrooks.     

Fine structural and histochemical studies on salivary glands of Peripatoides novae-zealandiae (Onychophora) with special reference to acid phosphatase distribution

The Onychophora feed on small arthropods and produce saliva when ingesting prey. Although saliva undoubtedly helps to liquefy the food its constituents have not yet been fully described. The salivary glands, two long tubes of glandular epithelium, are known to secrete a powerful protease, however, besides other enzymes and mucus. In Peripatoides novae-zealandiae there are protein-secreting cells of three types, referred to here as columnar, cuboidal and modified cells, and mucus cells. The anterior two-thirds of the gland show most cell diversity, while the posterior region consists mainly of columnar cells. These are the most numerous elements overall and they probably secrete salivary protease. In thick resin sections the granules of all protein-secreting cells stain strongly with methylene blue. Those of columnar cells are markedly uneven in size and accumulate distally, eventually filling the cytoplasm. More proximal Golgi regions may be discernible. Mucus cells are all of one type and their secretion droplets are stained lightly by methylene blue. The electron microscope shows that distal microvilli, desmosomes and septate junctions are common to all gland cells. In columnar cells, secretory material is contributed by Golgi complexes and by rough endoplasmic reticulum. Early secretory vacuoles containing dense material are seen in the concavity of Golgi regions. They are precursors to larger condensing vacuoles whose contents have a more flocculent appearance, and which may attain 3–4 μm in diameter. These evolve into secretory granules, usually of uneven texture, which are up to 2–5 μm in diameter. Histochemical tests for acid phosphatase show moderate amounts of enzyme throughout the gland. In whole mounts and sections the strongest reaction is in a band of cuboidal cells along the anterior median border. Columnar cells show a diffuse cytoplasmic reaction towards the base and sometimes distal to the nucleus, and mucus cells may also react strongly round the nucleus. Cytoplasm near the lumen shows little reaction. The secretory granules do not appear to contain active enzyme. Under the electron microscope a positive reaction for acid phosphatase is seen in lysosomal derivatives near the base and lateral periphery of gland cells. These bodies are probably autophagic vacuoles and they may contain membranous whorls and possibly old secretion granules. Acid phosphatase is involved also in the elaboration of new secretory granules in both columnar and mucus cells. Dense reaction product is found in a system of interconnected tubules and cisternae near the innermost face of the Golgi complex, which is interpreted as GERL. Acid phosphatase is present in the peripheral zone of adjacent early secretory vacuoles, and interconnections occur between GERL and secretory vacuoles. It is suggested that GERL tubules containing the enzyme may fuse with early secretory vacuoles and release acid phosphatase at their periphery. The acid phosphatase reaction is negative in large condensing vacuoles and most secretory granules. These findings are consistent with what is known from mammalian cells, including those of salivary glands.     

The reproductive response of the sea urchins Paracentrotus lividus (G.) and Psammechinus miliaris (L.) to a hyperproteinated macrophytic diet

The sea urchins Paracentrotus lividus and Psammechinus miliaris are submitted to the same environmental conditions in the Bay of Brest. The relationship between seasonal changes in food source quality and their gonad production was investigated in reproducing experimentally these conditions. In a first stage two macroalgae (Palmaria palmata and Laminaria digitata) were tested. P. miliaris showed a stronger preference for P. palmata and over a year-long experiment both urchins progressively preferred P. palmata. Seasonal variations in the chemical composition of P. palmaria were observed in the Bay of Brest: total carbohydrates were important and the relative maximum (about 50%) was reached between February and August; the lipid level was low and had a relative maximum of about 1% in June and August. Total protein in P. palmaria was high compared to other seaweeds: the maximum value (25%) was observed in June, which was probably due to the maintenance of nitrogen nutrient in the bay.In the second stage of the study, seasonal changes in biochemical components of ingestion and absorption of the two sea urchins were followed in the laboratory using a monospecific diet of P. palmaria. The patterns of total carbohydrates and lipid absorption were very similar for both sea urchin species. Carbohydrates were absorbed strongly and uniformly, year round. Lipid absorption mimicked the lipid nutrient pattern in the food source. Only changes in protein absorption varied slightly between the two urchin species. Protein absorption was maximal for both species in February and June, but the quantity of absorbed protein was significantly higher in P. miliaris than in P. lividus during February. This increase was concomitant with protein storage in the sea urchin gonads, which peaked in February for P. miliaris and in June for P. lividus. P. lividus had a higher gonad production efficiency, based on gonad yield. The comparison between in situ data and the experimental results suggests that an algal diet more nitrogenous than the in situ algal food source would benefit the herbivorous P. lividus, rather than the more omnivorous species P. miliaris. Although P. milaris has been described as a species with large gonad production potential, P. lividus appears to be a more suitable species for echiniculture conditions.     

Predation by small mobile aquatic predators regulates populations of the intertidal limpet Patella vulgata (L.)

Highly mobile aquatic predators are known to forage in the intertidal during periods of immersion. There is limited quantitative information, however, on the extent to which these predators influence the abundance of grazing molluscs which are known to have a key role in structuring intertidal assemblages. Our preliminary video observations revealed that crabs and small fish were abundant on shores in southwest England during high-tide. We then used manipulative experiments to quantify the effect of small mobile aquatic predators on the abundance of limpets (Patella vulgata L.). On the lower shore at two moderately sheltered rocky shores three treatments were established: complete cage, partial cage (cage control) and uncaged (natural condition). The complete cages excluded all predators. The partial cage treatment allowed full access to small predators and the uncaged treatment allowed access to all predators. After two months, limpet abundance in uncaged and partial cage treatments had declined by around 50% compared to the complete cage treatment. Population structure also changed with survival of larger individuals being greater than smaller individuals in the open and partial cage treatments compared to the complete cage treatment. The effects of excluding predators were consistent at small (meters) and large spatial scales (kilometres) and hence, it would appear that the outcomes of our research are generally applicable to similar shores in the region.To explore the mechanism behind the differential effects of predators according to prey size, we compared the detachment force required to remove limpets of differing sizes from the shore. This was around four times greater for larger individuals than for smaller ones indicating that smaller limpets were more vulnerable to predation. These effects were also consistent between locations. Subsequent laboratory observations showed that the crabs Carcinus maenas (L.), Necora puber (L.) and Cancer pagurus (L.) which are locally abundant predators of limpets, had differing handling behaviour but were all highly efficient at removing limpets from substratum. Hence, shell width and attachment force appeared to be critical factors influencing the vulnerability of limpets to predation by these crabs. Limpets are known to control the abundance of macroalgae on shores in the North-east Atlantic and so our conclusions about the role of mobile predators in regulating the abundance of these grazers are important to our broader understanding of the ecology of these shores.     

Tide-model analysis of the zonation of intertidal prosobranchs. I. Four species of littorina (L.)

Experiments were carried out in a tide model to determine the patterns of zonation of four species of periwinkles under laboratory conditions. Both upper shore littorinids, Littorina neritoides (L.) and L. saxatilis (Olivi), showed the same zonation in relation to the tidal cycle as observed on the shore at Plymouth. In the model, the animals adopted a zone above the level of high water and then remained inactive. L. littoralis (L.) showed the same distribution unless fucoid algae were provided, in which case the periwinkles clustered on them. L. littorea (L.) showed the ability to adopt a pattern of zonation in the model, which was at, and just below, high tide level, but higher than that normally observed on the shore.     

Interactions of Patella and macroalgae with settling Semibalanus balanoides (L.)

Biological interactions affecting densities of settling and newly-settled Semibalanus balanoides (L.) have been investigated by manipulative field experiments on the Isle of Man.The effects of sweeping by fucoid clumps of different species and Patella browsing have been compared on moderately-exposed shores. Patella allowed barnacle settlement by preventing growth of competing green algae, but reduced post-settlement densities. Small clumps of Fucus spiralis L., F. vesiculosus L, and F. serratus L. all reduced settlement considerably more so than limpets. F. serratus had the greatest sweeping effect.Interactions between macroalgae and Semibalanus balanoides have been investigated at all levels on sheltered shores and low down on more exposed shores. In the Fucus spiralis and F. vesiculosus zones, post-settlement numbers were higher than in adjacent areas where the canopy was removed. Barnacles did not settle readily in the Ascophyllum zone in either experimental or control areas. Settlement occurred in the upper part of the Fucus serratus zone in experimental areas where the canopy was removed but not in control areas. No settlement occurred in either treatment or control areas lower in the F. serratus zone. At all levels on the shore fucoid canopies seemed to reduce cyprid settlement, but the effect was greatest amongst F. serratus where there was total prevention. High on the shore the effect of enhanced post-settlement survival under the canopy outweighs reduction of cyprid settlement thus there are greater numbers in the controls. Competition with red algal turfs was shown to set the lower limit of the barnacle zone on a vertical pier face.     

Oxygenation properties of haemoglobins from the flatfish plaice (Pleuronectes platessa) and flounder (Platichthys flesus)

Summary The oxygen binding properties and some haematological data of haemoglobins of plaice (Pleuronectes platessa) and flounder (Platichthys flesus) were measured and compared, with the view of discerning their adaptations to the benthic habitat.Compared to plaice, flounders posses higher haematocrit and haemoglobin levels, and their haemoglobin has a higher oxygen affinity, smaller Bohr and Root effects and appears to have a greater ATP sensitivity. At pH 7.6, the half-saturation oxygen tensions,P ₅₀, of stripped plaice and flounder haemoglobins amount to about 5.9 and 4.2 torr, and the Bohr shifts (logP ₅₀/ pH) to –0.51 and –0.34, respectively. The species differences in the oxygen binding patterns occur after stripping the haemoglobin in solution, from dissolved ions and thus appear to be inherent in the pigment molecules. The differences suggest that the haemoglobin of flounder is better adapted to hypoxic and hypercarbic environments than plaice haemoglobin, in accordance with the more inshore occurrence of the former species.The molar ratios of ATP to haemoglobin tetramers are low in plaice and flounder (about 1.6); in plaice this ratio corresponds to that where the cofactor effect is most pronounced. In contrast to previous evidence for an adaptive reduction in the temperature dependence of the haemoglobin of flounder but not of plaice from the Baltic Sea (Friedrich, 1935), the same temperature effects were found in representatives of the two species both from the Dutch North Sea and the Danish Kattegat.