This study describes the reproductive behaviour of silver bream, Blicca bjoerkna, in an aquarium environment with hormonal injection, constant temperature and natural photoperiod conditions. The results revealed that the reproductive behaviour of silver bream was polyandrous with courting tactics including a high level of tactile stimulation and following behaviour developed by the males, but without territorial or aggressive acts. The individual participation of males in mating acts showed a significant positive correlation with the individual participation of males in following a female. A successful spawning act included trembling movements and violent splashing while eggs and sperm were released on plants. The female mated with one to five males without an active inter- and intra-sexual selection.
Biometric relationships between bone dimensions and body size are presented for topmouth gudgeon Pseudorasbora parva and sunbleak Leucaspius delineatus, two invasive fish species in the UK. This study also provides a tool for identification of these species using key bones. Such information facilitates the assessment of the potential role of these invaders in the diet of piscivorous fauna.
e determined regression relat ionships between head bone lengths and body size (standard length and weight) in chub Leuciscus cephalus and Eurasian perch Perca fluviatilis, two species taken frequently by the otter in the River Lee catchment. All relationships yielded significant linear equations, whereas those for bone vs. body weight were logarithmic. Regression slopes for head bones do not differ greatly within species but do across species of the same family.
The effect of water temperature and flow on the migration of fish was observed using weekly inspections of a fishpass on the lowland section of the River Elbe (Střekov, Czech Republic) from spring to fall 2003 and 2004. The effect was examined separately for immature (up to 2 years old) and adult fish and also the most abundant species (roach Rutilus rutilus, bleak Alburnus alburnus, chub Squalius cephalus, gudgeon Gobio gobio). More than 13 thousand fish from 23 species were recorded in the fishpass during both years. The highest levels of fish occurrence in the fishpass were observed during the spring spawning migrations of adults (April-May) as well as during the late summer and fall migrations of adult and immature fish (September-November). While the total number of both fish age categories was significantly related to the interaction of water temperature and flow, however, responses of individual species and age categories differed from each other. The numbers of adult bleak, chub and gudgeon increased with higher temperature. The maximum numbers of adult bleak migrated at medium values of temperature (15-20 °C) and flow (140-270 m3 s–1). The abundances of adult chub and adult plus immature gudgeon were higher with higher flow. The numbers of immature bleak and chub decreased with increasing flow. The numbers of adult and immature roach were influenced only by water flow with maximal numbers migrating under medium values of flow. Generally, we observed that immature fish and small- and middle-sized species required lower values of water flow than adult fish or large species to facilitate their movement. The exception was gudgeon, which required higher values of flow for its migration, a feature that could be related to its bottom dwelling nature or rheophily.
Diel feeding patterns of subadult and adult cyprinids of three species (roach Rutilus rutilus, bream Abramis brama, bleak Alburnus alburnus), which foraged almost exclusively on microcrustacean plankton, were studied in the meso-eutrophic Římov Reservoir (Czech Republic). All cyprinids showed a daytime feeding periodicity, with a marked night-time decline in gut fullness. Diel variations in gut fullness were observed in roach 200–270 mm standard length (SL) and bream 220–330 mm SL during May and in bleak, roach and bream of 110–170 mm SL, respectively, during August. Our results corroborate other studies in which light intensity has been found to be an important factor affecting cyprinid foraging on zooplankton. Daily zooplankton consumption rates ranged from 1.5 % of wet body weight in bream (220–330 mm SL) to 9.9 % of wet body weight in bleak (110–170 mm SL).
Significant numbers of juvenile (age 0+) and subadult (age 1+ and 2+) fish were observed migrating through a lowland pool fish pass (Elbe River, Czech Republic) from August to October in 2003 and 2004. Records of weekly catches totalled 2 148 (2003) and 6 469 (2004), mainly bleak Alburnus alburnus , barbel Barbus barbus, roach Rutilus rutilus and dace Leuciscus leuciscus. Fish migrated in the upstream direction probably to search the feeding grounds and refuges and their numbers corresponded to spring spawning migrations in the same fishpass and the year.
To estimate the size of fish taken as prey by piscivorous predators, linear or non-linear relationships between bone measures (pharyngeal, opercula, cleithra, anal and dorsal spine bones, otoliths) and body length were elaborated for eleven Eurasian cyprinid fish species captured in three lakes of Turkey: rudd Scardinius erythrophthalmus, Baltic vimba Vimba vimba, Danube bleak Chalcalburnus chalcoides, gibel carp Carassius gibelio, roach Rutilus rutilus, silver bream Blicca bjoerkna, common carp Cyprinus carpio, chub Leuciscus cephalus, Dnieper chub Petroleuciscus borysthenicus, tench Tinca tinca and tarek Alburnus tarichi (endemic species for Lake Van). All calculated regressions were highly significant, with coefficients of determination >81% in most of cases. The results suggest that the biometric relationships between fish length and some bones (pharyngeal, opercula, cleithra) are well suited for use in prey-predator studies of all the studied species, but otoliths and the dorsal and anal spines can be used for some fish species only (rudd, Baltic vimba, roach, silver bream, gibel carp).