Although zebrafish (Danio rerio) is a highly studied organism on many fields of research, many aspects of its basic biology still elude the scientific community. Its response to temperatureespecially developmental one -has been very scarcely studied and this is an important lack of knowledge since the species is considered quite eurythermal in nature. In the present study, zebrafish was subjected to four different developmental temperatures (22, 25, 28 and 31°C) from the half-epiboly stage until after metamorphosis in order to examine whether the temperature can influence the juvenile's phenotype. Morphometric and meristic characters were explored. Body shape and almost all of the meristic characters studied were significantly affected by the temperature applied during the first stages of development. Most meristic characters of the study, presented a significant differentiation in the extreme temperatures used (22 and/or 31°C), whereas lower temperatures seemed to produce higher meristic counts in the majority of the characters. Zebrafish juveniles, as shown in this study, exhibit highly variable phenotypes (phenotypic plasticity) induced by diverse thermal conditions during their early ontogenetic stages possibly in order to successfully adjust to different environments.

BackgroundThe noble crayfish (Astacus astacus) displays a complex historical and contemporary genetic status in Europe. The species divergence has been shaped by geological events (i.e. Pleistocene glaciations) and humanly induced impacts (i.e. translocations, pollution, etc.) on its populations due to species commercial value and its niche degradation. Until now, limited genetic information has been procured for the Balkan area and especially for the southernmost distribution of this species (i.e. Greece). It is well known that the rich habitat diversity of the Balkan Peninsula offers suitable conditions for genetically diversified populations. Thus, the present manuscript revisits the phylogenetic relationships of the noble crayfish in Europe and identifies the genetic make-up and the biogeographical patterns of the species in its southern range limit.ResultsMitochondrial markers (i.e. COI and 16S) were used in order to elucidate the genetic structure and diversity of the noble crayfish in Europe. Two of the six European haplotypic lineages, were found exclusively in Greece. These two lineages exhibited greater haplotypic richness when compared with the rest four (of “Central European” origin) while they showed high genetic diversity. Divergence time analysis identified that the majority of this divergence was captured through Pleistocene, suggesting a southern glacial refugium (Greece, southern Balkans). Furthermore, six microsatellite markers were used in order to define the factors affecting the genetic structure and demographic history of the species in Greece. The population structure analysis revealed six to nine genetic clusters and eight putative genetic barriers. Evidence of bottleneck effects in the last ~5000 years (due to climatic and geological events and human activities) is also afforded. Findings from several other research fields (e.g. life sciences, geology or even archaeology) have been utilized to perceive the genetic make-up of the noble crayfish.ConclusionsThe southernmost part of Balkans has played a major role as a glacial refugium for A. astacus. Such refugia have served as centres of expansion to northern regions. Recent history of the noble crayfish in southern Balkans reveals the influence of environmental (climate, geology and/or topology) and anthropogenic factors.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0971-6) contains supplementary material, which is available to authorized users.

Osteological development of Seriola dumerili is described and illustrated based on 141 specimens (3.9-27.0 mm TL) reared under semi-intensive culture conditions (Greece). The ontogeny of the vertebral column started with the formation of the neural arches (4.6 mm TL) and continued with the haemal arches and the centrum (4.8 mm TL). Until the end of the study, the centrum (12.5 mm TL) and neural arches (23.8 mm TL) were fully formed, while the haemal arches were not. The first skeletal elements of the fins started developing in the pectoral (3.9 mm TL), anal (4.8 mm TL), caudal (4.8 mm TL), dorsal (6.0 mm TL) and pelvic fins (6.3 mm TL), while the fin rays followed a slightly different pattern pectoral (5.6 mm TL), caudal (5.3 mm TL), anal (6.2 mm TL), dorsal (6.3 mm TL) and pelvic fin rays (7.0 mm TL). The ontogeny of the skeletal parts are compared with those of other Carangidae and Teleosts.