Fertility of roach × bream hybrids, Rutilus rutilus (L.) ×Abramis brama (L.), and their identification

Adult roach, bream and their presumed F₁ hybrid from an Anglian Water reservoir were identified on the basis of morphological and meristic characteristics. The hybrid was clearly intermediate. Four hybrid breeding crosses were induced to spawn by hypophysis. A bream × roach cross (female named first) failed to produce fertile eggs, whereas F₁ hybrid × roach, roach × F₁ hybrid and F₁ hybrid × F₁ hybrid all produced fry. Fertility (defined as survival of eggs to hatching) was high for the F₁ hybrid × roach back-cross (56%) but low for the others (<2%), in comparison to the pure species controls (roach 69%, bream 76%). Progeny from these crosses were reared until anal fin rays could be counted. These counts indicated intermediacy between the parents and back-crossed individuals, and similarity between F₁ hybrids and their F₂ progeny.     

RAPD fingerprinting of common bream Abramis brama L., roach Rutilus rutilus L., and their F1 hybrids

The polymerase chain reaction with arbitrary primers (RAPD-PCR) was used to study and to evaluate the genetic variation in the hybrid progeny of two Cyprinidae species, common bream Abramis brama and roach Rutilus rutilus. Genetic polymorphism was studied in 20 fishes (young of the current year) obtained in four individual crosses: R. rutilus x R. rutilus (RR), A. brama x A. brama (AA), R. rutilus x A. brama (RA), and A. brama x R. rutilus (AR). Amplification spectra obtained with eight primers contained 288 fragments, 97.6% of which proved to be polymorphic. The proportion of polymorphic fragments was 75.0% in the RR progeny, 58.1% in the AA progeny, 84.9% in the AR progeny, and 77.8% in the RA progeny. Classification analysis in the space of principal components was performed with the first four components, which together accounted for 64% of the total variance of the character under study. The individual contributions of components I, II, III, and IV were 26.8, 16.8, 11.5, and 8.9%, respectively. Fishes of the two pure species and the hybrid progeny (direct and reverse hybrids together) were clearly differentiated in the space of principal components I and II. The best differentiation of the four samples (RR, AA, RA, and AR) was observed in the space of principal components II and IV. Possible causes of high genetic variation in interspecific hybrids are discussed.     

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.     

Mechanism of hybridization between bream Abramis brama and roach Rutilus rutilus in their native range

Mechanisms of hybridization between bream Abramis brama and roach Rutilus rutilus were studied within the native range of the species in a lake in southern Finland. Through the genetic analysis of A. brama, R. rutilus and putative hybrids, hybridization is shown to have occurred between female A. brama and male R. rutilus. These results match with previous findings from introduced habitats, suggesting that mating between female A. brama and male R. rutilus is the predominant mechanism through which the two species hybridize.     

Ontogenetic changes in haemoglobins in roach, Rutilus rutilus (L.) and rudd, Scardinius erythrophthalmus (L.)

The haemoglobins and globins of the roach, Rutilus rutilus (L.) and the rudd, Scardinius erythrophthalmus (L.) have been studied by starch gel electrophoresis. At all stages of development studied, the roach and rudd haemoglobins give a similar electrophoretic pattern, the young fish of about 2 cm standard length possessing three separate haemoglobins, of which two bands only persist in the adult. The evolutionary significance of multiple haemoglobins in fishes is briefly discussed.     

A search for introgressive hybridization in the rudd, Scardinius erythrophthalmus (L.), and the roach, Rutilus rutilus (L.)

Rudd, roach and their hybrids from an interbreeding population at Norwich were examined electrophoretically for seven enzymes; an examination of pharyngeal teeth supplemented the data. The rudd were compared to rudd from Lake Trawsfynydd, Wales, a lake free from roach. No differences were observed between the rudd from the two localities and no evidence was found of introgression within the fish from Norwich.     

Fertility in first-generation hybrids of roach, Rutilus rutilus (L.), and silver bream, Blicca bjoerkna (L.)

Fertility in first‐generation hybrids of roach, Rutilus rutilus, and silver bream, Blicca bjoerkna, was investigated. Sperm and egg production of hybrids at first sexual maturity were examined. Eggs from female hybrids were artificially fertilized with the sperm of a corresponding hybrid male; a hybrid male from the reciprocal crossbreeding; a parental species male R. rutilus; and a parental species male B. bjoerkna. The results revealed that gametogenesis was normal in female hybrids. However, in male hybrids, a low efficiency of gametogenesis was observed. The semen of male hybrids was extremely dilute, with spermatozoa concentration lower than that in parental species. Nevertheless, these F1 hybrids (males and females) from reciprocal crossbreeding were fertile. F2 and backcross generations were produced, but F2 crosses from the female hybrid and corresponding hybrid male displayed a drastically slower hatching rate. Also higher proportions of deformed embryos were hatched than in other post‐F1‐generation crosses.     

The behavioural basis of prey selection by underyearling bream (Abramis brama (L.)) and roach (Rutilus rutilus (L.))

SUMMARY. A clear difference in the ability lo escape from fish predators exists between members of the Cladocera and Copepoda. The results of our laboratory studies have shown that underyearling roach and bream both found copepods more difficult to capture than cladocerans. However, bream were far more efficient than roach at catching the more elusive copepod prey. The basis for this difference was the greater strike ability of bream, most likely related to its more protrusible mouth. In their natural environment the two species of fish exhibited food resource partitioning with planktonic Cladocera predominating in roach guts and copepods and non-planktonic Cladocera composing the vast majority of the gut contents of bream. Differences in diet are partly due to their contrasting attack abilities. Additional variation may arise because of subtle differences in the timing and location of foraging.     

The biology of bream, Abramis brama (L), and its natural hybrid with roach, Rutilus rutilus (L), in the River Exe

Hybrids between bream, Abramis brama , and roach, Rutilus rutilus , occur in the lower reaches of the River Exe and were positively identified by their meristic features and shape of the pharyngeal bone. The growth of bream and hybrids was determined by back-calculation from scales. Annual checks were laid down in early June. The mean length for age of female bream was significantly larger than that of males for fish 6 years of age and older. This divergence in growth rate was associated with the sexual maturation of the fish. Data for the sexes were combined and compared with the growth rate of hybrids and roach from the same region. Hybrid growth was similar to that of bream for the first 6 years of life but was intermediate between that of the two parent species in the older age groups. Some hybrids with developing gonads were found. A change in the diet of bream from planktonic feeding to a benthophagic habit with age was noted. Detritus, substrate and chironomid larvae formed the bulk of the diet of hybrids.     

Effects of temperature and food on the free amino acids in tissues of roach (Rutilus rutilus L.) and rudd (Scardinius erythrophthalmus L.)

• 1.1. In liver and muscle the concentrations of free amino acids (FAA) are highest in fish maintained at low temperature and fed mealworms. These effects are more pronounced in roach than in rudd.
• 2.2. In the liver alanine, glycine and glutamate are the dominant FAA but proline increases in mealworm-fed animals.
• 3.3. In muscle, histidine and glycine dominate, except that a mealworm diet leads to an increase in the concentration of proline and to a concomitant decrease in the concentration of glycine.
• 4.4. Starvation leads to a reduction of total FAA content but to relative increases of lysine and histidine. These two FAA can serve as indicators of the general state of nutrition of roach and rudd.
• 5.5. The molar ratio [gly]/[his] is strongly correlated with temperature, decreasing with an increase in the temperature to which the animals had been exposed prior to capture.
• 6.6. The patterns of free and bound amino acids diverge more widely in these species than in mammals which reflects the greater dependence of the FAA pools of fish on intrinsic and extrinsic factors.
• 7.7. The concentrations of histidine in the FAA pools of muscle and in food proteins are strongly correlated.

     

Parasite fauna of bream Abramis brama and roach Rutilus rutilus from a man-made waterway and a freshwater habitat in northern Germany

Fifty specimens each of bream Abramis brama and roach Rutilus rutilus were examined for metazoan parasite fauna and trichodinid ciliates; 25 specimens of each species were collected from the Kiel Canal, a man-made waterway, and a nearby freshwater lake, the Dieksee. This is the first detailed parasitological examination of A. brama and R. rutilus at these locations: 30 parasite species were found, comprising 4 protozoans, 4 myxozoans, 5 digeneans, 3 monogeneans, 2 cestodes, 6 nematodes, 2 acanthocephalans, 3 crustaceans and 1 hirudinean. The crustacean Caligus lacustris occurred in both habitats while 2 other crustacean species, 2 acanthocephalans and 1 hirudinean were recorded exclusively for the lake habitat. Larval as well as adult stages of the different parasite species were found, indicating that both fish species act as intermediate and final hosts in both habitats. The Kiel Canal (total of 17 parasite species) showed a lower parasite species richness for A. brama and R. rutilus (14 and 10 parasite species, respectively) than the lake (25 parasite species). A. brama had a higher parasite richness (22 species) than R. rutilus (16 species) in the lake habitat. Most parasites collected were of freshwater origin. Consequently, the observed infection pattern of both fish species in the waterway is mainly influenced by the limited salinity tolerance of freshwater parasites, which are negatively affected even by a salinity of 2.3 to 4.5. In the central Kiel Canal, neither fish species was infected with marine parasites of low host specifity. These parasites are either limited by the low salinity at this sampling site (<4.5 to 6.0) or they cannot enter the canal due to the environmental conditions prevailing in this artificial brackish water habitat. Thus, the canal may comprise a natural barrier preventing the distribution of North Sea parasites into the Baltic Sea. However, the brackish water Baltic Sea nematodes Paracuaria adunca and Cosmocephalus obvelatus were found in R. rutilus from the canal, demonstrating the ability of some parasite species to invade and extend their range of distribution through this man-made shipping route from the Baltic to the North Sea.     

Hybrids of Abramis brama with Scardinius erythrophthalmus and Rutilus rutilus from Lake Volvi, Macedonia, Greece

Two specimens of the hybrid Abramis brama × Scardinius erythrophthalmus and a single specimen of the hybrid A. brama × Rutilus rutilus are reported and described from Lake Volvi, Macedonia, Greece. This is the first occurrence of either hybrid in Greek fresh waters.     

Success of embryonic development of reciprocal hybrids of bream Abramis brama (L.) and white bream Blicca bjoerkna (L.)

Success of embryonic development of reciprocal hybrids of bream Abramis brama and white bream Blicca bjoerkna was tested under laboratory conditions. Fertilization and embryonic development success of hybrids until hatching was high and comparable to that of pure species.     

Reproductive behaviour and sexual production in the first‐generation hybrids of roach Rutilus rutilus L. × common bream Abramis brama L

The aim of this study was to further test the viability of the roach Rutilus rutilus × common bream Abramis brama hybrid in terms of reproductive behaviour and sexual production. Egg release, mating and aggressive acts in reproductive behaviour, as well as absolute fecundity and sperm density in milt for sexual production were examined in the first generation of these hybrids at their first sexual maturity. The F2 and backcrosses of hybrids were also studied. The results revealed that these hybrids expressed a normal and typical mating behaviour, producing viable gametes. Under experimental reproduction between hybrids (hybrid reproduction), the number of egg‐release acts (range, 21–66) was nearer (χ² test, P > 0.05) the number of mating acts (11–65). Moreover, hybrid males exhibited territorial and aggressive behaviours. However, in experimental reproduction of female and male hybrids mixed with parental males (mixed reproduction), the egg‐release act and the mating act were inhibited by the intense territorial and aggressive activities of the common bream male. Absolute fecundity values (median, <2.2 × 10³ eggs) and sperm density (<7 × 10⁹ spermatozoa ml^?1) of hybrids showed a greater decrease (U test, P < 0.05) than in parental species (median, >6.0 × 10³ eggs and >14 × 10⁹ spermatozoa ml^?1, respectively). Nevertheless, these hybrids were fertile. F2 and backcross generations were produced, although with a significantly lower viable hatching rate (FEP test, P < 0.05) in F2 individuals from the female and its corresponding hybrid male (<6%), indicating a very low chance of survival in rivers.     

Factors affecting prey selection by young bream Abramis brama and roach Rutilus rutilus: insights provided by parallel studies in laboratory and field

Synopsis Prey selection by underyearling bream and roach was studied in both the laboratory and field. When presented with cladoceran and a more elusive copepod prey both fish species select against copepods, regardless of the relative prey sizes. However, the field diet of bream, but not roach, consistently includes a large proportion of copepods. The explanation for this discrepancy lies in the timing and location of foraging in the field. Bream foraging, unlike that of roach, is largely restricted to the hours of darkness and to the lowest stratum of the lake. The Microcrustacea of this stratum is depleted of cladocerans at night, because of vertical migration, and is relatively rich in copepods.     

Vertebral abnormalities in common bream Abramis brama (L.)

Vertebral abnormalities in bream Abrama bramis (L.) and lesions of the caudal peduncle are described.     

The adaptation of digestive enzymes to temperature, season and diet in roach Rutilus rutilus L. and rudd Scardinius erythrophthalmus L. Cellulase

The cellulolytic activity of the contents of the intestinal tract of populations of roach and rudd in four Tyrolean lakes was studied. Much of the activity was taken up with the diet. In fish feeding on plants and detritus a lower cellulolytic activity was found than in fish feeding on zooplankton or on arthropods. A seasonal pattern of cellulolytic activity was demonstrated with a peak in the autumn. It is assumed that the cellulolytic activity found in the intestinal contents of cyprinids is insufficient for the digestion of fibre, but that is suffices—particularly in omnivorous species—to support the breakdown of cell walls.     

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.     

Diet composition and prey preference of tench, Tinca tinca (L.), common bream, Abramis brama (L.), perch, Perca fluviatilis L. and roach, Rutilus rutilus (L.), in two contrasting gravel pit lakes: potential trophic overlap with wildfowl

The abundance of benthic macroinvertebrate taxa and the relative abundance of zooplankton taxa were compared with the diet of bream, tench. perch and roach from two gravel pit lakes during May-July 1986 and 1987. Significant food preferences were demonstrated between species and between lakes. Chironomid pupae dominated the macroinvertebrate diet of perch, roach, ate predominantly either Spirogyra sp. (St Peters Lake) or Daphniu hyalina (Main Lake).
The Main Lake, bream fed largely upon chironomid larvae and the bivalve Sphuerium but in St Peters Lake they positively selected a variety of less abundant benthic invertebrate taxa. Bream switched from benthos to zooplankton in the Main Lake in 1986. Tench ate large numbers of Aselhs and showed positive selection of various macroinvertebrate prey in St Peters but ate D. hjulim in Main Lake. Tropic overlap for chironomids and other macroinvertebrate prey was demonstrated between perch, bream and tench, and potentially with wildfowl which used the gravel pits for breeding and wintering.