Pattern formation of the ‘Tilapia mark’ in the tilapia fish, Oreochromis mossambicus

Abstract

The dorsal fin of the larval and juvenile Oreochromis mossambicus exhibits a unique black spot known as the ‘Tilapia mark’. We traced its development and found that it occupied a specific position in the dorsal fin bounded by rays 15 and 20. Ablation experiments carried out on the larval dorsal fin showed that this spot region constituted a developmental positional field. This positional field in the fin could regenerate and re‐establish the spot pattern despite repeated perturbation. The re‐establishment of spot was not simply due to fin injury since ablation of the non‐spotted region of the dorsal and the tail fin did not result in aggregation of melanophores. We propose that that‘Tilapia mark’ is a result of positional information in operation.