Organogenesis and Behavioral Changes during Development of Laboratory-reared Tiger Puffer, Takifugu rubripes

Abstract

Correlation between organogenesis and behavioral changes during development of laboratoryreared Tiger puffer, Takifugu rubripes is reported. In the head and trunk of newly hatched larvae, underdeveloped free neuromasts were already recognizable. From newly hatched to 3 days old, the number of sensory cells in a free neuromast remained constant, the cones and rod cells appeared in the retinae, and the larvae exhibited intense rheotaxis. Phototaxis changed from positive to negative at 3 days old. During larval growth, the number of free neuromasts increased. Neuromasts finally appeared over the whole body until 35 days old. In the trunk, two types of free neuromasts, one with maximum sensitivity in the antero-posterior direction, and the other with maximum sensitivity in the dorso-ventral direction, were observed. The former type predominated. In the head, free neuromasts were located around the eyes and nostrils. Maximum sensitivity of these neuromasts were tangential to their line-up in concentric circles around the eyes and nostrils. The free neuromasts on the trunk were embedded in the epidermis, and the first canal neuromasts appeared in the head region at 50 days old, when the juveniles became completely benthic dwelling.
Cannibalism began at 6 days old, when the digestive system became functional, and the larvae started independent swimming in the aquarium. Mortality from injuries caused by cannibalism increased with the formation of beaked jaw teeth at 35 days old, but decreased at 50 days old. At this age scales were formed on the dorsal and ventral sides of the body. Based on this study, morphological characters such as pigmentation on the caudal peduncle, and formation of minute tubercles on the ventral and dorsal skin surfaces, may be useful for estimation of age in wild caught larvae and juveniles.