BOLZ and LOUGH: GROWTH OF LARVAL COD AND HADDOCK 



As with the cod, larval haddock growth was 

 exponential from the predicted hatch length of 3.54 

 mm through the size range analyzed (12.7 mm). For 

 the first month of life, haddock grew at an average 

 rate of 0.21 mm/d. Hatching dates for the haddock 

 larvae occurred from 21 April to 21 May (Fig. 7). 



In both cod and haddock larvae, it was not always 

 possible to determine accurately the number of 

 increments deposited prior to the yolk-sac check; 

 consequently, size at hatch could be slightly less than 

 predicted. However, since an average of only 3 

 increments were noted between the nuclear and yolk- 

 sac checks in the clear otoliths, any error incurred 

 would have little effect on the calculated growth 

 curves. 



DISCUSSION 



The present work on cod and haddock concurs with 

 the day- increment relationship found in many recent 

 studies offish otoliths (Mugiya et al. 1981; Tanaka et 

 al. 1981; Uchiyama and Struhsaker 1981; Watabe et 

 al. 1982; Lough et al. 1982). The exponential growth 

 rates generated by the regression of standard length 

 on otolith age (increments) agree with the findings of 

 most previous field (Anderson 1982) and laboratory 

 analyses of cod and haddock larvae. Length-at-age 

 data for Southern New England cod from laboratory 

 rearing experiments (Laurence et al. 1981) were 

 highly correlated (r = 0.98) with the growth model 

 derived for cod larvae in the present study. A 35-d- 



old cod larva raised at the maximum feeding ration of 

 3 prey/ml had an uncorrected length of 10.75 mm 

 which closely agrees with the estimated length from 

 the growth curve of 10.52 mm. Gjosaeter and Tilseth 

 (1982) depict an otolith from a preserved 5.1 mm 

 North Sea cod larva with the same number of 

 increments (9) as predicted by the growth model. 

 However, Steffensen's (1980) work on daily growth 

 increments of juvenile East Baltic cod does not agree 

 with these studies. The number of increments re- 

 corded by him are much lower for a given length than 

 were found in the present analysis, e.g., a 60 mm fish 

 with only 46 increments. His results should be 

 viewed with caution, as he states that the central por- 

 tion of his otoliths was blurred and "that an unknown 

 number of growth zones in the central part of the 

 otolith have escaped detection." 



It is necessary to examine the central portion of the 

 otolith carefully in order to establish when daily 

 increment formation is initiated, as there is consider- 

 able variation between species (Brothers et al. 1976). 

 The intercept values of 4.82 mm for cod and 3.54 mm 

 for haddock derived from the growth model fall 

 within the range of reported hatching lengths for the 

 two species collected previously in the Gulf of Maine 

 (Colton and Marak 1969). An intercept of 4.75 mm 

 calculated from length-at-age data for larval and 

 juvenile cod collected in Woods Hole, Mass., and 

 tabulated by Bigelow and Schroeder (1953) also 

 compared closely with the estimate for cod larvae. 

 Brothers and McFarland (1981) noted 3 diffuse 



UJ 



a: 

 cr 



LI- 

 ES 



COD - SHADED BHRS 

 HR0D0CK - UNSHADED BRRS 



"l 



10 20 



BPRIL 



10 

 MAT 



ESTIMATED HATCH DATE 



FIGURE 7. — Estimated hatch dates for Atlantic cod and haddock larvae collected during spring 1981 on 

 southeastern Georges Bank based on otolith age (no. of daily increments). 



833 



