The population density, growth rate and production of bream, Abramis brama, in Tjeukemeer, the Netherlands

A method of estimating the population density of bream in Tjeukemeer (21.3 km²) using 16 690 introduced fish (fin-clipped and opercular tagged) is described. Gill nets of the winter fishery proved to be a more effective method of sampling the population for marked fish than fyke nets. The population density of bream (⋝25 cm) was estimated to be 180 000. There was no significant difference between the estimates derived from fin-clipped and opercular tagged fish. The growth rate of bream in Tjeukemeer (L_∞=41 cm) is poor compared with that of bream in other waters, due to its high density and the scarcity of zoobenthos available to it.
The production of bream (I–XV) is estimated to be 34 kg ha⁻¹ of which 25% is contributed by two (1959, 1963) strong year classes. Of a total biomass of 37.5 kg ha⁻¹ available to the fishery in 1969 only 2.7 kg ha^−l was removed as yield. The average P/B ratio for the population was low (0.39). It is concluded that a major flow of energy to bream is through zooplankton.     

Growth,condition and gonad development of bream (Abramis brama L.) in relation to its feeding conditions in Tjeukemeer

The bream (Abramis brama L.) population of Tjeukemeer was studied for three successive years. The growth, condition, gonad development, diet and feeding conditions of the fish are described. Food competition for two years with the then abundant young planktivorous smelt (Osmerus eperlanus) and perch (Perca fluviatilis) resulted in a decreased growth rate, condition and gonad development of the larger bream. The biomass of chironomids was too small in relation to that of the zooplankton to be important for the bream population, although they were eaten more efficiently.     

A note on the growth-rate and year-class strength of bream, Abramis brama (L.), in three eutrophic lakes, England

In this study some comparative observations on the growth-rate and year-class strength of bream, Abramis brama , in three Shropshire-Cheshire meres are given. All populations are exposed to variable recruitment. The occurrence of four strong year-classes (1959, 1966, 1969,1973) suggests that climate is an important factor influencing spawning success. Water temperatures ≥16°C in July and August may be particularly important. All other intervening year-classes are absent. The growth-rate of bream in Tatton Mere and Ellesmere Mere is good ( L ∞= 541–561 mm) but comparatively poor ( L ∞= 448 mm) in Cole Mere. The significance of population density, food supply and parasitic infestation by Ligula intestinalis is discussed.     

A model for switching between particulate-feeding and filter-feeding in the common bream,Abramis brama

Synopsis A model has been developed to describe the process of switching between particulate- and filter-feeding in common bream, Abramis brama, in relation to fish size and zooplankton density. The model assumes that the encounter rate of fish and zooplankton is determined by the density of zooplankton and the swimming speed of fish. However, if zooplankton density is so high as to allow at least one prey to be engulfed per random snap, the encounter rate is determined by the volume of the buccal cavity and by zooplankton density, but is independent of swimming speed. The snapping frequency will be maximal at the time of switching, decreasing with increasing zooplankton density because of the extra time needed for intra-oral prey handling. The model predicted switching from particulate- to filter-feeding only for bream> 15 cm standard length at zooplankton densities < 500 l^-1. The snap frequency of six size classes of bream (7.5, 10.4, 12.5, 15, 24 and 29.5 cm) was measured at varying densities of Daphnia. The model predictions for snap frequencies of all size classes corresponded to the highest values observed. The average of the observed snap frequencies was only 50% of the predicted values, probably because the calculated average distance between prey animals assumed an ideal swimming route of the fish and error-free vision for particulate-feeding, and the handling time was ignored.     

A test of a model for planktivorous filter feeding by bream Abramis brama

Synopsis The planktivorous feeding of bream, Abramis brama on Daphnia hyalina and Bosmina coregoni was analyzed in a stepwise regression analysis with the average size (and standard deviation) of consumed organisms as dependent variable and the size of the fish, the average size (and standard deviation) of the organisms and their density in the environment as independent variables. Three basic predictions on filter feeding were formulated and tested. It was predicted that the (average) prey size should increase with fish size, but that the standard deviation should decline. Secondly the prey size should be strongly correlated with the prey size available and thirdly the prey density should have little effect on the size selection. These hypotheses could not be rejected for bream>10 cm feeding on B. coregoni and for bream>20 cm feeding on D. hyalina. The hypotheses were not valid for smaller bream as these acted as particulate or combined filter- and particulate feeders.     

X-ray measurements of gill-arch movements in filter-feeding bream, Abramis brama (Cyprinidae)

The technique of X-ray cinematography was used to study pharyngeal movements in Abramis brama (L.). The theoretical and practical problems in X-ray cinematography of feeding fish are discussed, as well as criteria for the selection of images suited for detailed measurements.
Respiration and filter-feeding on Daphnia pulex (length c . 1 mm) show different gill arch movement patterns in bream. Slits between gill-arches are kept smaller during filter-feeding. In addition, during filter-feeding, this inter-arch distance decreases considerably in a posterior direction. The hypothesis that particle retention occurs on the slits formed between adjacent gillarches and their gill-rakers is not supported by the present results.     

Foraging capacities and effects of competitive release on ontogenetic diet shift in bream, Abramis brama

Bream (Abramis brama) undergo ontogenetic diet shift from zooplankton to benthic macroinvertebrates, but the switching size may be highly variable. To unravel under what conditions bream are pelagic versus benthic foragers, we experimentally determined size‐dependent foraging capacities on three prey types from the planktivory and benthivory niche; zooplankton, visible and buried macroinvertebrates. From these data we derived predictions of size‐dependent diet preferences from estimates of prey value and competitive ability, and tested these predictions on diet data from the field. Planktivorous foraging capacity described a hump‐shaped relationship with bream length that peaked for small bream of 67 mm total length. Benthivory capacity increased with increasing bream size, irrespective if benthic prey were visible on the sediment surface or buried in the sediment. From the experimental data and relationships of metabolic demand we calculated minimum resource requirement for maintenance (MRR) for each of the prey categories used in experiments. MRR increased with bream size for both zooplankton and visible chironomids, but decreased with bream size for buried chironomids, suggesting that intermediate sized bream (120–300 mm) may be competitively sandwiched between small and large bream that are more competitive planktivores and benthivores, respectively. Prey value estimates and competitive abilities qualitatively predicted diet shift in a bream population being released from competition. Competitive release did not change the diet of the largest size‐class feeding on an optimal diet of benthic invertebrates both before and after competitive release. However, profound diet shifts towards benthic macroinvertebrates were recorded for intermediate size‐classes that fed on a suboptimal diet prior to competitive release. Thus, laboratory estimates of size‐dependent foraging capacity of bream in planktivorous and benthivorous feeding niches provided useful information on size‐specific competitive ability, and successfully predicted diet preference in the field.     

The migration of ultrasonic-tagged bream, Abramis brama (L), in Lake Constance (Bodensee-Untersee)

From May to October 1983 the migration of six adult bream was examined by long-term ultrasonic tagging experiments. Two different migration types were observed: diurnal rhythmical migrations between the littoral and pelagic zones, and sporadic locomotions such as spontaneous excursions of several kilometers distance. At night, during their sojourn in the shallow littoral zone, bream feed intensively on benthic organisms; during their stay in the pelagic areas they presumably feed on zooplankton. Sporadic changes of place enable the bream to feed on locally abundant food resources. During the spawning season, migration contributes to successful spawning.     

On the biology of bream, Abramis brama (L.) in Lake Peipsi in 1994

The population of bream in L. Peipsi was studied with respect to age, growth rate, condition factor (according to Fulton) and length-weight relationship in 1994. That autumn the bream population in L. Peipsi consisted of fishes aged from 0+ to 15+. During the first year bream reached an average body length of 7.9 cm (the commercial legal size (30 cm) was usually attained by the end of the 5th–6th year. The condition of bream in this lake was above the average of Estonian lakes. The relatively good growth rate and condition of bream in the lake indicates that the waterbody is appropriate for this fish.     

Experimental research on the feeding of bream (Abramis brama L.) and white bream (Blicca bjoerkna L.)

Summary The feeding efficiency (the amount of food organisms (chironomids) eaten per unit time and weight raised to the power 0.8) of bream and white bream was determined in relation to the grain size of the substrate, in which the food was presented. Sand was used as substrate with a grain size up to 1500 , divided in eight fractions. The bream used had lengths of 14 and 33 cm and the white bream had a length of 21 cm.The experiments showed quite clearly that the grain size of the substrate influenced the feeding efficiency of all these fishes. An increasing grain size resulted in an decreasing feeding efficiency, because only up to a definite grain size the substrate can be filtered through the gill rakers. If the grain size is larger, the substrate cannot be sieved and is spit out. The size at which this switch occurred was different for all the fishes. For the small bream it was 350 , for the large bream 500 , and for the white bream 600 .Comparing the feeding efficiencies for a grain size which can be sieved by all these fishes, no significant difference was found between large bream and white bream. The small bream, however, was less efficient. Probably this difference is caused by the different sucking capacities of small and large fish. The small bream cannot in one time suck in the chironomids presented at 1 cm depth, while large bream and white bream can. So both grain size and depth at which the food was presented differentially determined the feeding efficiency of these fishes.     

A molecular approach to detect hybridization between bream Abramis brama, roach Rutlius rutilus and rudd Scardinius erythrophthalmus

Hybridization between roach Rutilus rutilus , bream Abramis brama and rudd Scardinius erythrophthalmus was investigated using morphological and genetic analysis employing both nuclear (ITS1) and mitochondrial (cytochrome b ) markers. Allele-specific amplification (ASA) reactions for both markers were developed and ITS1 sequence data for all three species are presented. Sequencing detected two ITS1 haplotypes within both roach and bream which most likely evolved in isolation and were subsequently brought together as a result of restocking by anglers. Analysis of cloned hybrid nuclear ribosomal DNA revealed evidence of recombination between parental ITS1 sequences. ASA proved to be an effective method for identifying hybrids and detected multiple ITS1 copies in fishes identified as purebred by morphological analysis. In addition this suggests post-F1 hybridization and introgression may be occurring between roach and bream, and rudd and bream, although some barriers appear to be suppressing backcrosses within the hybrid population. Analysis of the hybrid population demonstrated that hybridization has occurred in both directions.     

Long-term changes in the parasite fauna of the bream Abramis brama L. in eutrophicated lake

Data on the dynamics of parasite fauna if the bream Abramis brama for 50-year period are presented. The relation between trophic status of the reservoir, preferred type of the bream feeding, and the abundance of its parasites is shown. It was established, that the number of parasites developing in plankton organisms increases during the period of intensive eutrophication. Recent data on the parasite fauna of bream indicate preferred feeding of the host on benthic invertebrates, that is favourable to its growth. Permanent tendency to the increase of the bream invasion by the Diplostomum metacercaria could be a reliable parasitological indicator of the water body eutrophication.     

Effect of picrotoxin on the Cl-activated ATPase microsomal fraction of bream brain (Abramis brama L.)

It is found that picrotoxine in range concentrations 0.1-10 microM stimulates the basal Mg(2+)-ATPase from microsomal fraction of fish bream (Abramis brama L.), however decreases activating effect of 10(-5) M GABA on the enzyme. The stimulative effect of picrotoxine dependants on duration of preincubation with microsomes. It was established that basal Mg(2+)-ATP-ase activity was activated by anions (Cl- > Br- > I-). The activated effect of anions on the Mg(2+)-ATP-ase is decreased in the presence 1 microM picrotoxine. It was shown that in the dependence on concentration of the Mg(2+)-ATP (0.2 or 1 mM) in the incubation medium the picrotoxine serves as on activator or inhibitor of the enzyme activity. It is supposed that picrotoxine allosterially influences on the enzyme by the receptor-dependent way.     

Influence of temperature,rate of feeding and body weight on nitrogen metabolism of bream,Abramis brama L

• 1.1. Measurements of the rate of nitrogen consumption, total nitrogen and ammonia excretion and nitrogen absorption of bream, Abramis brama L. (body weight range 0.4–519 g wet wt) were made at 10, 15 and 20 C.
• 2.2. Fish were fed once daily on live zooplankton collected in Lake Balaton and cultured Tubifex sp. at 5–15% of their body weight.
• 3.3. Fish size and temperature had a combined effect on the rate of total nitrogen excretion. Total nitrogen excretion did not increase proportionally with an increase in consumption.
• 4.4. On average, 52–80% of the nitrogen consumed with food was excreted by bream.
• 5.5. The greatest part of total nitrogen excretion was ammonia and its proportion in the total ranged between 53 and 75%.
• 6.6. Temperature did not have any significant effect on the proportion of excreted ammonia and the rate of excreted total nitrogen was the only factor determining its proportion in the total.
• 7.7. The rate of nitrogen absorption of bream was surprisingly very high.

     

Structure,development and function of the branchial sieve of the common bream,Abramis brama,white bream,Blicca bjoerkna and roach,Rutilus rutilus

Synopsis The filter feeding organ of cyprinid fishes is the branchial sieve, which consists of a mesh formed by gill rakers and tiny channels on the gill arches. In order to establish its possible role during growth we measured the following morphological gill raker parameters over a range of sizes in three cyprinid fishes, bream, white bream and roach: inter raker distance, bony raker length, raker width, cushion length and channel width. At any given standard length common bream has the largest inter raker distance, roach the lowest and white bream is intermediate. In the comb model of filter feeding the inter raker distance is considered to be a direct measure of the mesh size and retention ability (= minimal size of prey that can be retained) of a filter. For the three species under study there is a conflict between the comb model and experimental data on particle retention. Lammens et al. (1987) found that common bream has a large retention ability whereas roach and white bream have a much smaller one. A new model, the channel model (Hoogenboezem et al. 1991) has been developed for common bream; in this model the lateral gill rakers can regulate the mesh size of the medial channels on the other side of the gill slit. The present data indicate that this model is not appropriate for white bream and roach. At any given standard length white bream and roach only reach 70% of the raker length of common bream, which means that in this model the gill slits should to be very narrow during filter feeding. The gill rakers consist of a bony raker and a fleshy cushion. The bony rakers have a rather long needle-like part outside the cushion in bream, but not in white bream and roach which have blunt gill rakers. Blunt gill rakers are not suited to reduce the diameter of the medial channels. The comb model seems more appropriate for white bream and roach, but doubts about the validity of this simple model remain. The sum of the areas of the medial channels is an approximation of the area through which water flows in the filter. This channel area therefore gives an impression of the capacity or flow rate of the filter. With this capacity estimation and an estimation of energy consumption we calculated an energy ratio of filter feeding. The energy ratio decreases with increasing standard length with an exponent close to the expected exponent of -0.40. The energy ratio is highest in bream, intermediate in white bream and lowest in roach.     

The effect of seasonal changes on the activity of intestinal alkaline phosphatase of pike perch, Lucioperka lucioperka and of bream, Abramis brama

The effect of seasonal changes on the activity of intestinal alkaline phosphatase was evaluated in two types of fish grown in the Kurshskii bay of the Baltic sea. With the pike perch, Lucioperka lucioperka , higher enzyme activity and optimal temperature of activity were observed in the summer compared to winter, whereas with the bream, Abramis brama , essentially no difference in enzyme activity and in optimal temperature of activity was found between the two seasons. In both fish, the thermal stability of the enzyme and the activation energy of enzyme activity decreased in winter. The different biological nature of the two fish appears to be reflected in the response of the intestinal alkaline phosphatase to seasonal changes.     

A novel, endogenous inhibitor of 7-ethoxyresorufin-O-deethylase activity isolated from liver cytosolic fractions of bream (Abramis brama L.)

The cytosolic supernatant of bream (Abramis brama L.) liver homogenates inhibits the 7-ethoxyresorufin-O-deethylase (EROD) activity of pike (Esox lucius) microsomal fractions. The inhibitor shows no activity against 7-ethoxycoumarin-O-deethylase and benzo(a)pyrene hydroxylase indicating a high isoenzyme specificity. The inhibiting component is a heat-sensitive substance (56 degrees C for 5') which is not self regenerating after subsequent cooling. It can be isolated from the cytosolic fraction using two combined steps of ion exchange chromatography. The purification factor is 500-fold with a recovery rate of 70%. SDS-PAGE of the purified fractions indicate that electrophoretic purity was not achieved. However, a prominent band at about 97 kDa was present in all fractions in a close intensity activity relationship. The molecular weight of the native form of the purified protein was determined to be 175 +/- 35 kDa using gel filtration on a Sephacryl S 300 HR column. So far the inhibitor can be characterized as a protein. It shows strong tendencies to aggregate due to lipophilic interactions. These interactions can be repressed by the addition of 1% sodium cholate. The inhibitor has an optimum activity at 25 degrees C and pH 8.0. The inhibitor does not correspond to any of the known cytosolic, endogenous inhibitors of EROD activities in fish, including proteases, cytosolic phosphatases, kinases and resorufin reductase (e.g. DT-diaphorase), although a non-dicoumarol (10 microM)-inhibited menadione oxidoreductase activity of up to 46.7 +/- 0.4 nmol/min per mg inhibitory protein was measured. Kinetic studies using Michaelis-Menten kinetics with purified inhibitor fractions prove a non-competitive mode of inhibition. As this kind of inhibitor is not described yet it is named CERODIP (cytosolic, EROD-inhibiting protein).     

The role of behavioral polymorphism in the process of intrapopulation segregation of ecological niches in bream,Abramis brama (Cyprinidae)

The study of feeding and defensive behavior in the two groups of bream (Abramis brama) differing in the peroxidase locus (presented by Po79 and Po100 alleles) has been performed. The A group bream (homozygous by Po79 allele) exhibit higher locomotor activity and aggressiveness, actively feed in the presence of a predator, and adapt quickly to experimental conditions. The B group bream (homozygous by Po100 allele) exhibit lesser locomotor activity and practical absence of aggressiveness. These fish reject food in the presence of a predator, their behavioral characteristics after removal of the predator recover after a long time and they adapt to experimental conditions slowly. Thus, the study revealed that there really exists the intraspecies form of bream that is less reactive but more aggressive and agile in which conditioning responses develop better. Presence in a population of reactive and nonreactive specimens serves as a basis for the mechanism of regulation of acuteness of intrapopulation relations and range expansion. In the present case, this mechanism allows for the efficient use of alternative resources having inconstant availability.     

Lake water level increase during spring affects the breeding success of bream Abramis brama (L.)

In Lake Constance, Eurasian bream Abramis brama (L.) spawn in very shallow littoral areas by the beginning of May. They attach their adhesive eggs to pebble and cobble substratum at <40 cm depth. Increasing water levels before spawning inundate bare substratum to which bream eggs may attach better than to deeper substratum covered by epilithon. Consequently, the water level increase prior to spawning should determine the amount of pristine spawning substratum available to bream and thus influence their breeding success. In order to test this hypothesis, the influence of hydrology and climate on the abundance of age-0 bream was combined with the results from field investigations on the egg survival and abundance of age-0 bream. A strong positive correlation between the mean water level increase during the spawning season of bream (April–May) and the abundance of juvenile bream was found. In contrast, the absolute water level during spawning and during the nursery stage in summer, the cumulative temperature during the egg, larval and juvenile stages and two North Atlantic Oscillation (NAO) indices did not affect the abundance of juvenile bream. The field investigations confirmed that bream eggs attach better to and have higher survival rates on bare substratum than on substratum with epilithon cover. Accordingly, eggs within a spawning habitat of bream were most abundant between 10 and 20 cm depth, where the epilithon cover was lower than at depths exceeding 30 cm. The results of this study confirm an adverse influence of epilithon cover on the attachment and subsequent survival of bream eggs and emphasize the importance of spring inundations for the successful breeding of the bream. Handling editor: J. A. Cambray