Lordosis induction in juvenile red sea bream, Pagrus major, by high swimming activity
M. Kihara, S. Ogata, N. Kawano, I. Kubota, R.
Yamaguchi-2002
Aquaculture, 212(1-4): 149-158
Abstract:
Lordosis is correlated with absence or malfunction of
the swimbladder. However, swimbladder abnormalities do not completely
explain the occurrence of lordosis. We examined whether muscle activities
from vigorous tail beat induced by removal of the caudal fin could induce
lordotic malformation in juvenile red sea bream. We also attempted to
determine the minimal current velocity for inducing lordosis in relation to
total length (TL). For this purpose, we employed relative current velocity
in terms of "move of water in times of total body length per second (TL
s-1)". We compared effects of different water current (2 vs.
4 TL s-1) for 10 days on bone malformation using juvenile of
25-mm TL. Exposure to 4 TL s-1 current velocity, but not 2 TL s-1,
induced lordosis. Lordotic juvenile red sea bream had a cuneiform centrum
mainly at the 15th vertebra. Lordosis was observed in fish with normal
swimbladders as well. Thus, swimbladder abnormalities alone cannot
completely explain the occurrence of lordosis. We removed part or all of the
caudal fins of fish of 40-mm TL and exposed these fish to 2 TL s-1
current for 10 days. Control fish did not show deformations in the
vertebrae. Fish with complete removal of the caudal fin swam with vigorous
tail beats. However, fish with complete, upper or lower caudal fin removal
(36%, 29% or 7%, respectively) displayed lordosis even at the current
velocity of 2 TL s-1. These findings suggested that the muscle
activities from excess beat of the tail against excessive current, but not
the mechanical action of the caudal fin, induced lordosis.