Morphological development in relation to phototaxis and rheotaxis in the striped jack,Pseudocaranx dentex

Abstract

The development of sensory and swimming organs in striped jack Pseudocaranx dentex was morphologically and histologically analysed and compared with the development of phototaxis and rheotaxis. A major inflection of allometric growth occurred at 9 mm TL and a minor inflection occurred at 20 mm. At about 10 mm, fin ray formation was complete. Red muscle layers first appeared at 4.3 mm and increased to more than 10 layers at 12 mm. These morphological changes were considered to be essential for cruise swimming, which might help higher behaviours such as predator evasion, schooling and migration. Strong phototaxis showing a preference for a light intensity of 105 lux appeared at 3.5 mm (3 days old), corresponding with the development of pigment in the retina. The light intensity preference changed from 10 to 10 lux at 10–12 mm (23–25 days), when the rod formation was suggested. Rheotactic behaviour was apparent in 4.5 mm larvae. Canals of buccal lateral lines were formed from 8–18 mm, while those of trunk lateral lines were formed at 23–30 mm, suggesting that the canal formation is unnecessary for the rheotaxis.