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 development of the retinomotor reactions in larval plaice (Pleuronectes platessa, L.) and turbot (Scophthalmus maximus, L.)

The development of the retinomotor reaction was examined histologically in the larvae of plaice (Pleuronectes platessa, L.) and turbot (Scophthalmus maximus, L.). In plaice retinal pigment migration is present from hatching, but, in turbot, does not occur until just before metamorphosis. In both species rods first develop at metamorphosis. Plaice show cone migration, but this does not occur in turbot. During dark-adaptation retinal pigment contraction started at ≈ 100 lux in all stages of plaice. Before metamorphosis pigment was fully contractedimmediately below 1000 lux, but after metamorphosis full contraction did not occur until the light intensity had fallen to < 1.0 lux. The thresholds for cone migration in plaice showed similar changes, although the actual light intensities were about an order of magnitude lower. In turbot there was always an abrupt transition between light- and dark-adaptation; the thresholds for this fell from ≈ 10 lux at the start of metamorphosis to between 1.0 and 10 lux at the end. The lower threshold light intensities in turbot compared to plaice may indicate that vision is of greater importance in the feeding of the former species.     

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

The accumulation of inorganic mercury from sea water by plaice eggs, larvae, and adult fish has been studied using ²⁰³HgCl₂ as a tracer. The isotope was rapidly accumulated and the levels of accumulation have been related to stable element concentrations. High concentration factors were attained by many organs, but the distribution of the ²⁰³Hg was markedly different from that of the stable element. Whereas the largest fraction of the body burden of mercury is contained by muscle, only a slow rate of accumulation into this tissue was observed. In addition, the mercury in fish muscle is of the methyl form: no evidence for the methylation of the tracer was obtained.     

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 intertidal movements and distribution of young fish on a sandy beach with special reference to the plaice (Pleuronectes platessa L.)

The intertidal movements of young fish were studied on a sandy beach over several tidal cycles during the day and the night. Young plaice (Pleuronectes platessa L.), by virtue of their abundance, received the most attention, and it was found that they migrate up and down the beach with each tide in company with several other less abundant species. The dab (Limanda limanda (L.)), does not make this migration.The vertical distribution of the commoner fish species was charted and each was found to occupy a specific zone in relation to the water, but with large overlaps in many cases. A close relationship between the length of plaice and dabs and the depth in which they were caught was evident during the summer months, but this relationship broke down in the winter due mainly to an offshore movement of larger fish.The food intake of plaice was studied throughout the day and night; feeding occurred mostly during the day. No effect of the tide on feeding could be detected.The possible mechanisms controlling the tide-related movements and the size-depth relationship are discussed and a general hypothesis is put forward in which it is proposed that the fish are able to select and maintain their position at a particular depth throughout a tidal cycle thereby being guided up and down the beach. Attributes of depth which the fish might use as a reference point in their movements are discussed.     

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 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.     

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.     

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).     

Copper toxicity and copper tolerance in Enteromorphacompressa (L.) Grev.

The responses of ship-fouling and non-fouling isolates of Enteromorpha compressa (L.) Grev. have been compared in media containing copper at 0.0?9.6 μmol · dm^?3. The responses of each isolate were found to vary, according to the conditions of the original habitat. Thus ship-fouling E. compressa was found to be tolerant of copper concentrations up to 9.6 μmol · dm^?3 showing a maintenance of all of the physiological processes studied during the present research (cell viability, net photosynthesis, intracellular K⁺ and dimethylsulphoniopropionate content). Non-fouling plant material showed symptoms of copper toxicity at all levels of copper from 1.8 μmol · dm^?3 to 9.6 μmol · dm^?3. Copper tolerance in ship-fouling E. compressa appears to be genetically determined, since the progeny from ship-fouling plants are also tolerant to copper concentrations within the range 1.8 to 9.6 μmol · dm^?3. The rate of accumulation of copper in ship-fouling thalli is, however, almost identical to that of non-fouling thalli, suggesting that tolerance may be due primarily to internal detoxification, rather than an exclusion mechanism.     

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

Eighty-nine O-group plaice from a natural population were exposed at 15°C to heavy infection by Cryptocotyle lingua cercariae. Subsequently 45 fish were retained at 15°C, whilst 44 were held at 5°C. Both groups were sampled by killing individual fish at intervals of 6,18,42 h and daily thereafter up to 710 h. Entire fish were fixed immediately in formol saline, transversely sectioned and stained by H & E, PAS, PAS-diastase, JSDB 109, Picro-Mallory, Masson's trichrome, Gram-Weigert and Alcian blue. Histopathological observations showed: (a) epidermal lesions associated with encysted metacercariae in adjacent tissues; (b) myofibrillar necrosis associated with bacteria possibly introduced by the parasite; and (c) a reactive swelling of the intermuscular septa. The progressive development of the parasite cyst and host capsule is described. Development of both was markedly inhibited at the lower temperature, but the inflammatory response at either temperature was slight. This may be evidence of a long-standing host-parasite relationship which has evolved to an advanced state of adaptation on the part of the parasite and tolerance on the part of the host.     

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

Histological and ultrastructural examinations were carried out on the integuments of larval plaice from hatching to 60 days. The skin of the newly hatched larva consisted of a delicate epidermis overlying a fluid filled dermal space. As the fish matured this became thicker, the fibrous dermis developed and the mitochondrion rich 'chloride cells' degenerated. Around the 42nd day the eosinophil granule cell appeared in the basal layers of the epidermis and by the sixtieth day the epidermis could be considered fully developed.     

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.     

Azoreductase activity in the hard clam, Mercenaria mercenaria (L.)

The ability of the hard clam Mercenaria mercenaria (L.) to metabolize compounds containing an azo linkage has been investigated. The hepatopancreas has azoreductase activity as evidenced by the reduction of 1,2-dimethyl-4-(p-carboxyphenylazo)-5-hydroxybenzene. This activity was higher at 37°C than at 22°C and the pH optimum was 8.0. The reaction was stimulated by the addition of flavin mononucleotide and inhibited by air. Activity was found in both the 105,000 g soluble and the microsomal fractions of the hepatopancreas.     

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.     

An experimental study of the oxygen consumption,growth, and metabolism of the COD (Gadus Morhua L.)

The rate of oxygen consumption of cod in sea water at 12 °C containing MS222 (25 mg/l) can be expressed as: Q_o2 = 0.245 W^0,82(mg/h), where W is the lived weight of the fish (g). The maximum efficiency of conversion of assimilated food into growth was 24% during the feeding experiment. Digestion efficiencies were estimated at over 98% using fillets of plaice as food. The effect of increasing the rate of food intake was to increase liver weight and condition factor. The relative proportions of protein and lipid in the body did not change over the range of feeding levels used. The conversion efficiency had a maximum value at an intermediate feeding rate.