JONES: DETERMINING AGE OF LARVAL FISH 



through the larval stages, two parameters fun- 

 damental to application of the increment technique 

 to field populations can be determined: 1) age at first 

 increment deposition and 2) testing of daily incre- 

 ment deposition under artificial conditions. Age at 

 initial increment deposition for 18 species of fish is 

 listed in Table 1. Radtke (1978) speculated that in 

 species having slowly developing embryos, initial 

 deposition occurs at, or before, hatch; in species 

 having rapidly developing embryos, initial increment 

 deposition does not occur until yolk-sac absorption 

 or first feeding. This hypothesis is not substantiated 

 in the currently published literature. Information for 

 nine species of laboratory-reared fish larvae (Table 

 2) shows no such trend for data currently reported 

 in the literature Even for the same suborder, Clu- 

 peoidei, opposite development and initial increment 

 deposition patterns exist for herring (Clupea haren- 

 gus) and the northern anchovy. 



The Case for Daily Increment Deposition 



Seventeen species have shown consistent daily 

 deposition of increments under what are presumed 

 to be good conditions for growth. The species that 

 have shown daily increment deposition come from 

 both freshwater and marine habitats and encompass 

 a wide variety of lifestyles. In addition, six species 

 held in the laboratory and sampled over known 

 periods of time demonstrated daily increment 

 deposition (Table 3). Four investigation groups 

 (Struhsaker and Uchiyama 1976 for Stolephorus pur- 

 pureas, Taubert and Coble 1977 for Lepomis macro- 

 chirus, Campana and Neilson 1982, Wilson and 

 Larkin 1980 for Oncorhynchus nerka) brought lar- 

 vae and juveniles into the laboratory, reared them 

 for a period of time, then correlated increment 

 counts to days of captivity. Schmidt and Fabrizio 

 (1980) took consecutive samples from a field popula- 

 tion of Micropterus salmoides, which had a short 

 spawning period and correlated the time between 

 samples to the change in mean increment count. 



Lack of Daily Deposition Rates 



The most controversial results obtained so far 

 come from studies of increment deposition in larval 

 Clupea harengus (Table 1). Agreement for daily in- 

 crement deposition has not been obtained. Studies 

 that observed daily deposition by Gjosaeter 2 and 

 and Gj«isaeter and 0iestad (1981) indicate that 



2 Harold Gjdsaeter, Institute of Marine Research, P.O. Box 1870 

 5011 Bergen, Norway, pers. commun. February 1983. 



increments are deposited with roughly daily 

 periodicity and that initial increment deposition 

 begins at first feeding (4-5 d). Gjosaeter and 

 0iestad (1981) found that 99 increments were 

 formed in 97-d-old larvae. Gjosaeter, however, cau- 

 tioned that these results were based on small sam- 

 ple sizes. Lough et al. (1982) reported on larval her- 

 ring reared in the laboratory that lived until age 18 

 d. They did confirm that increment deposition began 

 at yolk-sac absorption, but did not find that the in- 

 crements were daily. In fact, only three increments 

 were laid down within 18 d. Lack of confirmation 

 of daily deposition is easy to dismiss, since the lar- 

 vae did not survive past 18 d. 



However, Geffen (1982) has demonstrated an inter- 

 action between growth rate and increment deposi- 

 tion rate. Only under circumstances of very fast 

 growth, 0.42 mm/d (a rate which is faster than 

 growth rates postulated for field animals) did incre- 

 ment deposition approach daily periodicity (0.92 in- 

 crements/d). It is noteworthy that the growth rates 

 in her study were related to container size; faster 

 growth occurs in bigger containers. The variance of 

 increment count at age is small and homogeneous 

 only under the fastest growth condition (Norway 

 Pond). The increasing variance with age in the other 

 conditions leads to the speculation that some of these 

 larvae were unknowingly starving. However, since 

 the slope of the regression line for the Norway Pond 

 condition is significantly different than 1 incre- 

 ment/d, this result cannot be dismissed. There would 

 be obvious value in repeating these experiments. Gef- 

 fen also found that increment formation did not 

 begin before yolk-sac absorption and was in agree- 

 ment with the other investigators on this point. The 

 literature (Table 1) shows only one case (Oncorhyn- 

 chus nerka) where independent investigators have 

 confirmed daily increment deposition (Wilson and 

 Larkin 1980; Marshall and Parker 1982). 



Geffen (1982) found that increment deposition was 

 also a function of growth in Scophthalmus maximus 

 (Table 4) under various conditions of temperature 

 and photoperiod. Under two conditions— 1) 20°C, 

 constant light, and 2) 24°C, 12L:12D— increments 

 were deposited daily For all other conditions in- 

 crements were not daily. Under all conditions, 

 deposition rate was a function of length. Although 

 Geffen did not point this out, comparisons of growth 

 at different temperatures can also be drawn from 

 the data. Larvae were grown under 20°C and 24°C, 

 both under a 12L:12D cycle. Larvae grew faster and 

 deposited more increments at 24°C. Such differences 

 in temperature might be used to explain differences 

 in increment deposition except that the other case 



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