INTERACTIVE EFFECTS OF AGE AND ENVIRONMENTAL 



MODIFIERS ON THE PRODUCTION OF DAILY GROWTH 



INCREMENTS IN OTOLITHS OF 



PLAINFIN MIDSHIPMAN, PORICHTHYS NOTATUS 



Steven E. Campana' 

 ABSTRACT 



Plainfin midshipman, Porichthys notatus, were reared in the laboratory under three environmental regimes to 

 determine the influence of certain variables upon otolith growth increment formation. Both larval and 

 juvenile midshipman were used to test diel cycles and constant conditions of light and temperature. Daily 

 growth increments were formed upon hatch unless a diel photoperiod was absent. However, under constant 

 light, an endogenous circadian rhythm became evident aftera 2-3 week acclimation period, resulting in daily 

 increment production. With increasing age, the influence of light as a zeitgeber decreased, while daily 

 increments became more prominent in all environments. Temperature fluctuation affected increment 

 appearance, but did not entrain increment deposition. 



Daily growth increments in the otoliths of fishes have 

 been observed in a large number of species (Pannella 

 1971; Brothers et al. 1976; Taubert and Coble 1977; 

 Wilson and Larkin 1980). These concentrically 

 formed increments may be counted or measured to 

 provide a chronological record of past fish growth. 

 Information on hatching date/age (Ralston 1976; 

 Struhsaker and Uchiyama 1976), daily growth rates 

 (Methot 1981), and timing of life history transitions 

 (Pannella 1980; Brothers and McFarland 1981) has 

 been derived from the examination of otolith micro- 

 structure. Such data are difficult to obtain from larval 

 and juvenile fishes by other means. 



Daily increments are produced through a diel 

 periodicity in the deposition of calcium carbonate on 

 the otolith (Mugiya et al. 1981). However, there is 

 some controversy as to the zeitgeber behind the daily 

 cycle of deposition, if indeed one exists. In a series of 

 experiments upon larval Lepomis, Taubert and 

 Coble (1977) determined that a 24-h light-dark cycle 

 was necessary to entrain an endogenous rhythm of 

 increment production. Reversal of the light-dark 

 cycle reversed the daily sequence of increment for- 

 mation in larval Tilapia (Tanaka et al. 1981). 

 However, 36-h "days" and constant light conditions 

 had no effect on daily increment production in 

 juvenile starry flounders, Platichthys stellatus (Cam- 

 pana and Neilson 1982). Similarly, constant light or 



institute of Animal Resource Ecology, University of British 

 < Columbia, Vancouver, British Columbia, Canada V6T 1W5; pre- 

 sent address: Marine Fish Division, Bedford Institute of Ocean- 

 ography, P.O. Box 1006, Dartmouth, Nova Scotia, Canada B2Y 



4A2. 



Manuscript accepted .July 198.'!. 



FISHERY BULLETIN: VOL. 82. NO. 1. 1984. 



dark conditions did not inhibit the formation of daily 

 increments in young chinook salmon, Oncorhynchus 

 tshawytscha (Neilson and Geen 1982). The con- 

 tradictory results of the above studies suggest that 

 photoperiod effects on increment production may 

 vary with age or species of fish. 



Other environmental variables may influence the 

 daily rhythm of otolith deposition. Diel temperature 

 fluctuation has been implicated as a factor in daily 

 increment production of temperate stream fishes 

 (Brothers 1981), although this suggestion has not 

 been supported by other studies (Campana and 

 Neilson 1982; Neilson and Geen 1982). Feeding fre- 

 quency may also influence otolith increment produc- 

 tion; fish given multiple daily feedings have been 

 reported to produce nondaily increments (Pannella 

 1980; Neilson and Geen 1982), although recent 

 studies suggest that feeding effects are limited 

 (Tanaka etal. 1981 ; Marshall and Parker 1982; Cam- 

 pana 1983). 



Confidence in the reliability of otolith microstruc- 

 ture examination requires knowledge of those factors 

 that may influence otolith increment production. 

 Conflicting results in the literature suggest that age 

 influences the response of daily increment produc- 

 tion to environmental variables such as photoperiod 

 and temperature. This study was undertaken to test 

 that hypothesis. Plainfin midshipman, Porichthys 

 notatus, were reared from the egg stage under various 

 light and temperature regimes; constant conditions 

 and diel cycles of each variable were tested. The 

 effect of the regimes on otolith microstructure was 

 noted for both newly hatched and juvenile fish. 



165 



