EFFECTS OF FEEDING REGIMES AND DIEL TEMPERATURE CYCLES ON 



OTOLITH INCREMENT FORMATION IN 

 JUVENILE CHINOOK SALMON, ONCORHYNCHUS TSHAWYTSCHA 



John D. Neilson' and Glen H. Geen'^ 



ABSTRACT 



The effects of constant and diel cyclic water temperature regimes, feeding frequency, fish activity, and 

 ration level on growth increment formation in juvenile chinook salmon, Oncorhynchus tshawytscha, 

 are described. Of the variables examined, any event which recurred more than once every 24 hours 

 increased the rate of increment production above 1 increment per 24 hours. The results were consistent 

 with the hypothesis that environmental variables modify the rate of increment formation by altering 

 the periodicity of fish activity. Both water temperature and ration level interacting with water 

 temperature affected otolith increment width, a measure offish growth, although ration level did not. 



To realize the potential of otolith microstructure 

 in detailed age and growth studies of fishes, 

 knowledge of factors influencing otolith growth is 

 required. The principle features of otoliths likely 

 to be used in such studies are the growth incre- 

 ments which are deposited in a concentric fashion 

 around the otolith nucleus. The frequency of depo- 

 sition (often 1 increment/24 h) and the width of the 

 increments are both affected by environmental 

 conditions (Neilson and Geen 1982). 



The growth increments result from accretion of 

 CaCO^ and to a lesser extent, protein (Simkiss 

 1974). The daily nature of their deposition ob- 

 served by many workers (Pannella 1971; Brothers 

 et al. 1976; Wilson and Larkin 1982; and others) 

 appears related to a daily rhythm in the relative 

 rates of calcium carbonate and protein deposition 

 (Mugiya et al. 1981). The cyclic deposition of cal- 

 cium and protein over a 24-h period results in the 

 formation of the bipartite features now referred to 

 as daily growth increments. 



The effects of environmental variables on 

 otolith increment formation have been the subject 

 of some controversy. Taubert and Coble (1977) con- 

 cluded that a 12:12 LD photoperiod was responsi- 

 ble for entraining diel rhythms in the growth of 

 juvenile Lepomis and Tilapia sp. otoliths. How- 

 ever, juvenile starry flounder, Platichthys stel- 



^ Department of Biological Sciences, Simon Fraser University, 

 Bumaby, B.C., Canada V5A 1S6; present address: Marine Fish 

 Division, Canada Department of Fisheries and Oceans, Biologi- 

 cal Station, St. Andrews, N.B., Canada EOG 2X0. 



^Department of Biological Sciences, Simon Fraser University, 

 Bumaby B.C., Canada V5A 1S6. 



Manuscript accepted February 1984. 

 FISHERY BULLETIN: VOL. 83. NO. 1, 1985. 



latus, and chinook salmon, Oncorhynchus 

 tshawytscha , continued to produce daily growth 

 increments when exposed to constant light (Cam- 

 pana and Neilson 1982; Neilson and Geen 1982). 

 The latter authors presented evidence that feed- 

 ing frequency affected both increment number 

 and width in O. tshawytscha . They also suggested 

 that feeding frequency (or any other environmen- 

 tal variable) was probably not the ultimate factor 

 determining the frequency of otolith increment 

 production. Environmental modulation of endo- 

 crine rhythms (Menaker and Binkley 1981) may 

 ultimately control otolith increment periodicity. 



Diel cycles in water temperature have received 

 little consideration as an environmental variable 

 potentially affecting increment formation. 

 Brothers (1978) suggested that diel temperature 

 variations were responsible for otolith increment 

 formation in temperate stream-dwelling fish al- 

 though no data were presented. This gap in our 

 understanding of factors influencing otolith in- 

 crement production is significant since diel 

 changes in water temperature are a common fea- 

 ture of aquatic environments. In this study we 

 examined the effects of diel water-temperature 

 regimes on formation of otolith growth increments 

 in O. tshawytscha alevins and fry. We also present 

 data on the effects of interactions of water- 

 temperature regimes, feeding frequency, and ra- 

 tion level on otolith increment formation in O. 

 tshawytscha fry. Finally, we tested the suggestion 

 made earlier (Neilson and Geen 1982) that feeding 

 periodicity (or any other periodic event affecting 

 fish activity) modifies the rate of otolith increment 

 production through changes in fish activity. 



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