Eco-ethological characteristics of two natural hybrids of Abramis brama (L.) from the River Meuse basin

Eco-ethology as expressed in migration patterns, abundance
level, growth rates in river conditions, and reproductive
behaviour in a controlled environment were investigated in
natural common bream x roach and common bream x silver
bream hybrids. From 2001 to 2003, hybrids and parental
species were captured in a fish pass trap at the Lixhe dam on
the Belgian Meuse river during their reproductive migration.
The fish pass was checked 3 days a week and the water
temperature was recorded hourly. The results showed that
hybrids were less frequent but they had migrated during the
same period and in the same environmental conditions as the
parental species. Scale readings showed that the growth of
hybrids was intermediate to the two parent species growth. In
reproductive experiments between hybrids under controlled
conditions, the female hybrid mated with one to two hybrid
males. In reproductive experiments with hybrids mixed with
parental species males, the female hybrid mated with male
hybrid and male roach or male silver bream, but not with the
male common bream. The succession of spawning episodes
in hybrids were those recognised in parental species.
Aggressive and territorial acts were observed among the
males of these hybrids in a territory including a spawning
substrate. This study has proven that the natural hybrids are
eco-ethologically viable.