Effects of low-salinity on
the growth and development of spotted halibut Verasper variegatus in
the larva-juvenile transformation period with reference to pituitary
prolactin and gill chloride cells responses
T. Wada, M. Aritaki, M. Tanaka-2004
Journal of Experimental Marine Biology and Ecology, 308(1): 113-126
Abstract:
Low-salinity adaptability was investigated in a
flatfish spotted halibut Verasper variegatus during the period from
late metamorphic larvae to early juveniles by a 20-day rearing experiment
under different salinity regimes (1, 4, 8, 16 and 32 ppt). Effects of
low-salinity on growth and development were examined and the changes in the
prolactin (PRL) production level in the pituitary and the gill chloride cell
morphology were examined as physiological backgrounds for low salinity
adaptation. PRL cells and chloride cells were identified by
immunocytochemistry with a specific antiserum for PRL188 and Na+,K+-ATPase.
Most of the fish exposed to over 4 ppt survived for 20 days, but all the
fish exposed to 1 ppt died within 5 days. Fish kept in intermediate
salinities (8, 16 ppt) grew significantly better than those in the control
group (32 ppt). Fish exposed to 4 ppt attained almost the same body length
as the control group at 20 days after transfer, although these fish showed
an abnormally dark body color as well as delayed development. These results
suggested that spotted halibut has a high-adaptability to low-salinity
environments and prefers an intermediate salinity near iso-osmolality (about
12 ppt) from the late metamorphic larval stage, but does not completely
adapt to a hypoosmotic of 4 ppt salinity or less than half of the
osmolality. The percentage of PRL-cell volume to pituitary volume was
significantly higher at 4 ppt than in the control group. The chloride cells
in gill filaments were significantly larger at 4 ppt than in the control
group. These results suggest that juveniles could adapt to a low-salinity
environment due to the activation of PRL production and enlargement of
chloride cells. These laboratory findings suggest that late metamorphic
larvae and early juveniles of spotted halibut may utilize a low salinity
environment such as estuarine tidal flats or very shallow coastal areas as
their nursery grounds in the sea.
(Division of Applied Bioscience, Graduate School of
Agriculture, Kyoto University, Kitashirakawa, Kyoto 606-8502, Japan, e-mail:
twada@kais.kyoto-u.ac.jp)