Effect of chronic ammonia
exposure on growth in juvenile Atlantic cod
A. Foss, S.I. Siikavuopio, B.-S. Sæther, T.H.
Evensen-2004
Aquaculture, 237(1-4): 179-189
Abstract:
The effects of chronic un-ionised ammonia (UIA-N)
exposure on growth and food conversion efficiency in juvenile Atlantic cod, Gadus
morhua, were examined. Fish with a mean (SD) initial weight 16.7 (3.4) g
were exposed to four concentrations of UIA-N, ranging from 0.0005 mg l−1
(control) to 0.17 mg l−1, for 96 days at 13 °C. Compared
to the control, growth was significantly reduced at UIA-N concentrations
above 0.06 mg l−1, but the fish experiencing the most
severe UIA-N concentrations still maintained high growth rates (>1% day−1).
The growth reduction is attributed to a decrease in food intake. Fish from
the exposed groups displayed an acclimatory response to UIA-N, as growth
rate reduction in these groups, compared to the control, diminished as the
experiment progressed, and in the last period, growth rates in the UIA-N
exposed groups were not significantly different from that of the control.
Concurrently, a reduction in plasma urea-N content was seen in these groups
at the end of the experiment, indicating an increased efflux of urea in
response to high ambient UIA-N.
(Akvaplan-niva,
Bergen Office, Nordnesboder 5, N-5005, Bergen, Norway, e-mail: af@akvaplan.niva.no)