Growth Priorities of the Four Riverine Cyprinids during Early Ontogeny

SIMPLE SUMMARY: The present study analyzed growth priorities during early development in four riverine cyprinid species. The allometric growth of the species studied is in line with the growth pattern typical of many fish species, where high allometric (rapid) growth of head and tail sections is observed at the beginning of the larval period and a clear tendency towards isometric (more balanced) growth at the end of the larval period. It was also observed that a lower level of ontogenetic development of fish after hatching was associated with higher growth rates during the first days after hatching. Specific to the species studied was the absence of abrupt changes in body proportions and the persistence of positive allometric growth in body size throughout the larval and juvenile periods, most likely related to a gradual change in behavior and habitat. ABSTRACT: Growth patterns during early development of four species of riverine cyprinids, common dace (Leuciscus leuciscus L.), ide (Leuciscus idus L.), chub (Squalius cephalus L.) and common barbel (Barbus barbus L.), over 30 days of rearing, were analyzed. The study period covered three successive phases of larval development (preflexion, flexion, postflexion) and part of the juvenile development. The growth analysis carried out in the present study shows that significant allometric growth occurred mainly in preferentially localized body parts (head and tail) and was also associated with an increase in body height. The replacement of temporary structures (e.g., fin fold absorption) and the appearance of definitive structures around 21 mm TL (beginning of the juvenile period) corresponds to a stabilization of the relative growth of most parts of the body. This is probably due to the fact that the studied species had completed the most important part of the remodeling process (metamorphosis) and had achieved a body shape that allows juveniles to colonize faster water habitats. The results also indicate that individuals of species that are less developmentally advanced at the time of hatching (common barbel, chub) show greater initial dynamics of change in growth rate than individuals of species whose individuals are more advanced in ontogeny (common dace, ide). In addition, the small differences observed in growth parameters between successive periods analyzed, supported by the results of previous studies on these species, probably reflect the lack of abrupt changes in the behavior and habitat of the species studied.