Marking zebrafish, Danio rerio (Cyprinidae), using scale regeneration

Tagging or marking small laboratory-bred fish species is not an easy task. This also holds for the zebrafish, Danio rerio, which is widely used throug hout the world as a model organism for genetics, developmental biology, etc . We present a simple marking technique based on scale regeneration. A comp arative morphological study of various types of zebrafish scales indeed sho ws that regenerated scales are easily distinguishable from nonregenerated o nes. We propose to take advantage of this typical morphology to mark a sing le or several individuals. This technique, based on a natural biological pr ocess, is easy to perform and does not enhance fish mortality in laboratory breeding conditions. It permits assembly of several specimens in a single tank with the possibility of identifying each of them by regenerated-scale coding. Nevertheless, a prerequisite is that the species does not lose and regenerate scales in large numbers in laboratory breeding conditions. To ch eck this, 5,200 scales were removed from a large region of the left flank i n 100 zebrafish and the number and position of regenerated scales were stat istically analysed. Our results indicate that (1) laboratory-bred zebrafish have only a few regenerated scales (7.48%), (2) the probability of finding a regenerated scale is similar whatever its position in a row (antero-post erior axis), but (3) it differs from one row to another (scales from the ba ck are more frequently lost than those from the pectoral region). This pape r presents a procedure to mark small breeding colonies of zebrafish using s cale regeneration with the number and position of the scales to be removed with high probability of marking success. (C) 2000 Wiley-Liss, Inc.