Les stratégies de reproduction chez les poissons labridés méditerranéens

In contrast to tropical environments, Mediterranean fish assemblages have been exposed to greater seasonal fluctuations of climatic factors (water temperature, photoperiod), which have impacted more or less significantly on the biology of fish. The labrid fishes (wrasses) are good examples of how climatic changes influence behavioural strategies. The European wrasses differ mainly from the tropical ones by their particular reproductive behavioural patterns. In these wrasses, the variety of the reproductive strategies (hermaphroditism or gonochorism, spawning seasonality in open water or on substrates, degrees of parental care, etc.) make it possible to study the evolution of these srrategies.

If in tropics, most of wrasses exhibit planktonic spawning, the Mediterranean ones adapted their behaviour, developing modes of reproduction unusual in the tropics : short periods of reproduction, spawning eggs on substrates or in elaborated nests, parental care. This evolution is dictated, in particular, by the pressure of climatic factors, such as water temperature, on the presence or the absence of parental care.

Of the 21 Mediterranean species, almost all the species studied lay their eggs on substrates or in a nest built by the large territorial male. Only Coris julis, Thalassoma pavo and Xyrichthys novacula (protogynous hermaphroditism fish species) spawn in open water (planktonic spawning) as tropical species do. Moreover, the majority of Symphodus males have complex social structures where nesting territorial males, satellite and sneaker males can be recognized. These sneakers adopt reproductive behavioural patterns known as alternative reproductive behaviour. They can either steal the spawn (streaking) or steal the female (sneaking). Finally, the majority of these Symphodus give parental care throughout each nesting cycle (2 to 5 nests are elaborated during the reproductive season in spring), which always comprises three phases : nest building phase (construction with alive algae of a substrate for spawning or a true nest in form of cup), sexual activity phase (the very moment the females come to spawn in the nest), and fanning phase (oxygenation of eggs, by the beat of the pectoral fins, until hatching).

The diversity of the biological and behavioural adaptations developed by numerous tropical and temperate species of labrid fishes allow us to consider the family as an ideal group to investigate various problems in behavioural ecology.