The effects of fluctuating
seasonal and constant water temperatures on the photoperiodic advancement of
reproduction in female rainbow trout, Oncorhynchus mykiss
B.
Davies, N. Bromage-2002
Aquaculture, 205(1-2): 183-200
Abstract:
A series of experiments were performed in order to
determine the effects of varying water temperature on the maturation of
female rainbow trout subjected to photoperiodic manipulation. Long-short
photoperiod regimes, i.e. long days of LD18:6 followed by an abrupt change
to short days of LD6:18, were used to advance or delay maturation to summer
months, producing commercially desirable out-of-season eggs. At the same
time, these fish were exposed to two different seasonal water temperatures
supplied by river (range 0-20.5 °C) or borehole (range 7.0-10.5 °C)
sources.
The photoperiod regime was seen to have the primary
effect on altering the timing of maturation and appeared similar,
irrespective of the prevailing water temperature. However, water temperature
had a modulating effect on time of maturation and ovulation; fish showing an
ability to delay the timing of final maturation and ovulation, when
temperatures were at extremes, high or low. Extreme temperatures, also, had
a major effect on the later stages of ovary development and subsequent egg
quality. When the major time of spawning was advanced to July-August, when
river water temperatures regularly approach 20 °C, a dysfunction in ovarian
development occurred, and no viable eggs were obtainable in these
conditions. When the maximum water temperature was reduced to 16 °C, fish
stripped in a normal fashion, but egg quality was significantly reduced.
Possible alterations in farming practice in order to improve egg survival in
such situations are discussed.
(Institute of Aquaculture, University of Stirling,
Stirling, FK9 4LA, UK, e-mail: briony.campbell@noaa.gov)