Normal table of postembryonic zebrafish development: staging by externally visible anatomy of the living fish.

The zebrafish is a premier model organism yet lacks a system for assigning postembryonic fish to developmental stages. To provide such a staging series, we describe postembryonic changes in several traits that are visible under brightfield illumination or through vital staining and epiflourescent illumination. These include the swim bladder, median and pelvic fins, pigment pattern, scale formation, larval fin fold, and skeleton. We further identify milestones for placing postembryonic fish into discrete stages. We relate these milestones to changes in size and age and show that size is a better indicator of developmental progress than is age. We also examine how relationships between size and developmental progress vary with temperature and density, and we document the effects of histological processing on size. To facilitate postembryonic staging, we provide images of reference individuals that have attained specific developmental milestones and are of defined sizes. Finally, we provide guidelines for reporting stages that provide information on both discrete and continuous changes in growth and development.

Sex-specific perceptual spaces for a vertebrate basal social aggregative behavior.

Loose aggregations of fishes, or shoals, are a basal social organization of vertebrates and offer a valuable opportunity to determine how individual perceptions influence group formation. We used zebrafish, Danio rerio, to comprehensively investigate the preference space for shoaling related to adult pigment pattern variation, presented in the form of 17 zebrafish pigment pattern mutants or closely related species. We examined all combinations of these phenotypes in 2,920 initial and replicated preference tests, and used as subjects both domesticated laboratory stocks and wild-caught fish. By using multidimensional scaling and other approaches, we show that laboratory and wild zebrafish exhibit similar preferences, yet, unexpectedly, these preferences differ markedly between sexes, and also from how human observers perceive the same pigment patterns. Whereas zebrafish males respond to two traits (species and stripe patterning) in deciding whether to join a shoal, zebrafish female preferences do not correlate with a priori identifiable traits, and neither perceptual world is correlated with that of human observers. The observed zebrafish sex differences run counter to the most commonly accepted explanations for the individual selective advantages gained by shoaling. More generally, these data describe very different perceptual worlds between sexes and reveal the importance of sex differences in social group formation, as well as the critical importance of defining species specificity in visual signaling.

Zebrafish in the wild: a review of natural history and new notes from the field.

The zebrafish, Danio rerio, has emerged as a major model organism for biomedical research, yet little is known about its natural history. We review the literature pertaining to the geographic range, biotic and abiotic habitats, and life cycle of the zebrafish. We also report our own field study to document several aspects of zebrafish natural history across sites in northeast India. We found zebrafish particularly abundant in silt-bottomed, well-vegetated pools and rice paddies adjacent to slow moving streams at a range of elevations. We further identified co-occurring fishes likely to be zebrafish competitors and predators. Finally, we present observations that indicate substantial habitat degradation and loss, and suggest guidelines for documenting and preserving natural zebrafish populations.

Timing and plasticity of shoaling behaviour in the zebrafish, Danio rerio.

The zebrafish has become a major model system for biomedical research and is an emerging model for the study of behaviour. While adult zebrafish express a visually mediated shoaling preference, the onset of shoaling behaviour and of this preference is unknown. To assess the onset of these behaviours, we first manipulated the early social environment of larval zebrafish subjects, giving them three model shoaling partners of the same pigment phenotype. We then assayed the subjects' preferences using binary preference tests in which we presented subjects with two shoals, one shoal of fish exhibiting the same pigment pattern phenotype as their models and another shoal with a radically different pigment pattern. To determine whether or not the visually mediated preference could be altered once it was established, we further manipulated the social environment of a number of subjects, rearing them with one model shoal and testing them, then changing their social consorts and retesting them. Our results demonstrate that larval zebrafish shoal early in their development, but do not exhibit a shoaling preference until they are juveniles. Moreover, we find that the shoaling preference is stable, as changing the social environment of fish after they had acquired a preference did not change their preference. These data will facilitate investigations into the mechanisms underlying social behaviour in this vertebrate model system.

Learned social preference in zebrafish.

How social aggregations arise and persist is central to our understanding of evolution, behavior, and psychology. When social groups arise within a species, evolutionary divergence and speciation can result. To understand this diversifying role of social behavior, we must examine the internal and external influences that lead to nonrandom assortment of phenotypes. Many fishes form aggregations called shoals that reduce predation risk while enhancing foraging and reproductive success. Thus, shoaling is adaptive, and signals that maintain shoals are likely to evolve under selection. Given the diversity of pigment patterns among Danio fishes, visual signals might be especially important in mediating social behaviors in this group. Our understanding of pigment pattern development in the zebrafish D. rerio allows integrative analyses of how molecular variation leads to morphological variation among individuals and how morphological variation influences social interactions. Here, we use the zebrafish pigment mutant nacre/mitfa to test roles for genetic and environmental determinants in the development of shoaling preference. We demonstrate that individuals discriminate between shoals having different pigment pattern phenotypes and that early experience determines shoaling preference. These results suggest a role for social learning in pigment pattern diversification in danios.