AGE AND GROWTH OF A PLEURONECTID, PAROPHRYS VETULUS, 



DURING THE PELAGIC LARVAL PERIOD IN 



OREGON COASTAL WATERS 



Joanne Lyczkowski Laroche, Sally L. Richardson, 1 and Andrew A. Rosenberg- 



ABSTRACT 



The age of 331 field-collected English sole, Parophrys vetulus, larvae, 3.1-20.0 mm SL, was deter- 

 mined using daily otolith growth increments. Age in days from hatching was estimated by adding 5, 

 the number of days prior to first increment formation in the laboratory, to the number of increments 

 counted on sagittae. Number of otolith growth increments among larvae of known age in the labo- 

 ratory ranged widely. Yet daily periodicity of increment formation in P. vetulus was inferred from 

 the observations that even under poor growing conditions some larvae added one increment each day 

 since first formation and that, unlike the remaining laboratory-reared larvae in which no pattern 

 was evident, increment addition among larvae in the sea appeared to follow a stable and uniform 

 pattern. 



Gompertz and von Bertalanffy growth models fitted the resultant size-at-age data equally well; 

 therefore, only the Gompertz model is presented. Larval growth rate decreased from 0.3 mm per day 

 at 8-9 days of age to <0.1 mm per day between 73 and 74 days. The oldest specimen was 74 days old. 

 but most of the larval and transforming specimens collected in plankton samples were <70 days old . 



Previous estimates of age at length of larval P. vetulus, based on length-frequency modal progres- 

 sion analysis, overestimated the age of larvae >5.5 mm SL by 2-3 times and, correspondingly, the 

 duration of pelagic life was overestimated, 18-20 weeks compared to 8-10 weeks based on otolith- 

 estimated age. 



Saccular otoliths grow by addition of layers of 

 material differing in the relative amount of the 

 protein, otolin, and calcium carbonate in the 

 aragonite form (Degens et al. 1969; Pannella 

 1971). This results in growth units or increments 

 composed of an inner light band and an outer 

 dark band. Once the cycle of formation has been 

 established for a species, otolith growth incre- 

 ments can be used to estimate a fish's age and as a 

 record of its past growth. Daily periodicity of 

 increment formation has been confirmed in 

 numerous species by the number of first-order 

 growth increments within annuli in fish over 1 yr 

 of age (Pannella 1971, 1974), by inspection of 

 otoliths from reared fish of known age (Brothers 

 et al. 1976; Taubert and Coble 1977), or from fish 

 maintained in the laboratory for a known period 

 of time (Struhsaker and Uchiyama 1976). Bands 

 of daily increments are often grouped into fort- 

 nightly and monthly growth patterns (Pannella 



'Gulf Coast Research Laboratory, East Beach Drive, Ocean 

 Springs, MS 39564. 



department of Oceanography, Dalhousie University, 

 Halifax, N.S., Canada. 



Manuscript accepted August 1981. 

 FISHERY BULLETIN: VOL. 80, NO. 1. 1982. 



1974; Rosenberg 1980). Subdaily increments, 

 which appear faint and indistinct, when com- 

 pared to daily increments, have been found in 

 some species (Taubert and Coble 1977; Brothers 

 and McFarland in press). 



The daily increment method of aging larval 

 and juvenile fishes can be used in fishery re- 

 search to document the timing and duration of 

 spawning, development, and major life history 

 stages and events. The singlemost important 

 application is the accurate determination of 

 growth rates during early life in the sea. This 

 technique has been applied to relatively few 

 species, however, and much remains to be 

 learned about how growth may change during 

 development and under varying environmental 

 conditions. Once specific growth rates are avail- 

 able, age-dependent larval mortality rates can 

 be estimated and used to improve estimates of 

 spawning stock biomass and also, perhaps, pro- 

 vide insight into recruitment success. 



This paper documents the existence of daily 

 growth increments in laboratory-reared and 

 field-caught larvae of an eastern North Pacific 

 pleuronectid, the English sole, Parophrys 

 vetulus. It provides the first accurate estimates of 



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