Acoustic telemetry reveals strong spatial preferences and mixing during successive spawning periods in a partially migratory common bream population

Partial migration, whereby a population comprises multiple behavioural phenotypes that each have varying tendencies to migrate, is common among many animals. Determining the mechanisms by which these phenotypes are maintained is important for understanding their roles in population structure and stability. The aim here was to test for the temporal and spatial consistency of migratory phenotypes in a common bream Abramis brama (‘bream’) population, and then determine their social preferences and extent of mixing across three successive annual spawning periods. The study applied passive acoustic telemetry to track the movements of bream in the River Bure system of the Norfolk Broads, a lowland wetland comprising highly connected riverine and lacustrine habitats. Analyses revealed that individual migratory phenotype was highly consistent across the 3 years, but this was not predicted by fish sex or length at tagging. During the annual spawning periods, network analyses identified off-channel areas visited by both resident and migrant fish that, in non-spawning periods, were relatively independent in their space use. Within these sites, the co-occurrence of bream was non-random, with individuals forming more preferred associations than expected by chance. These associations were not strongly predicted by similarity in fish length, sex or behavioural phenotype, indicating that the resident and migrant phenotypes mixed during their annual spawning periods. The results suggested these different phenotypes, with spatially distinct resource use in non-spawning periods, comprised a single population, with this having important implications for the management of this wetland resource.

FORMING OF SOME ORGANS OF HEMATOPOIESIS IN PRE-LARVAE, LARVAE AND FRY OF COMMON BREAM (ABRAMIS BRAMA L.)

Ability for hematopoiesis of spleen, intestinal mucosa, and liver is investigated for early ontogenesis of common bream Abramis brama L., a species of bony fish widespread in the Russian waters, including Astrakhan region. The samples (24 ind.) were collected in the fish farm in Kamyzyaksky district of the region in middle May 2018, after hatching. Histological analysis was made by conventional methods. Both spleen, liver, and intestinal mucosa were formed in the first days after hatching. In the spleen, such signs of hematopoiesis as dispersed new developing blood particles were found just in the first day. In the intestinal mucosa, the first foci of hematopoiesis appeared in the nineteenth day. These organs were formed completely by the end of larval development, and the most intense level of hematopoiesis was observed in that time, with forming of blood cells of all rows of hematopoiesis. On the contrary, no signs of hematopoiesis were found in the liver throughout the larval and juvenile periods.

Age and growth of common bream, Abramis brama (L.), caught at Hammam Debagh Reservoir (Guelma, northeast Algeria)

This study was conducted in Hammam Debagh Reservoir located in northeastern Algeria, which was first the subject of fish farming tests in 2001. The species tested included Chinese carp, royal carp, common carp, pikeperch, and common bream. The present work aimed to determine the age and growth of one of the most frequently caught species in the reservoir, common bream, Abramis brama. This information is essential to the knowledge of fish biology, and thereby to solving many of the problems of fish research and development. A sample of 100 common bream, A. brama, was caught with gillnets over a period of six months from December 2017 to May 2018. The results obtained fit well with the growth model and were similar to those published regarding other environments. Scales from a sample of 50 fish were read under an optical microscope, which permitted identifying five age groups. The value of the overall sex ratio (4.88) revealed a strong imbalance in favor of males throughout the study period. The relationship linking length-weight is of the minor allometry type with b < 3.

Numerical Model of Fish Exploitation – structure and application

Fisheries simulation models are tools used for forecasting the effects of exploitation and determining the directions of managing fisheries resources. The Numerical Model of Fish Exploitation (NMFE) and its capabilities were tested on a population of common bream, Abramis brama (L.) in a dam reservoir that is exploited by commercial and recreational fisheries. Based on the designated population parameters of N0, Fij, Mi, and ei and the size and structure of the common bream population in the reservoir, the model was used to examine hypothetical simulation variants of changes in fishing intensity E1 with nets and rods, changes in fishing intensity based on actual fishing effort with nets, changes in natural mortality, changes in the size of fish caught, and the impact of this on the size of the resources. Initial catches with nets and rods were calculated. Increasing fishing effort did not translate proportionally to increased catches, and the function was curvilinear. The results of simulations that reduced the intensity of fishing with nets and decreased catch sizes concurred with data from actual catches. Simulations of changes in natural mortality had various effects on the size of catches. Reducing parameter M did not impact the level of catches, while increasing parameter M reduced the size of catches significantly.