208 



Fishery Bulletin 102(1) 



Egg volume was calculated considering the anchovy egg 

 as an ellipsoid ( V=4jt x a x b x c/3, where a, b and c are the 

 ellipse radii). 



Statistical analyses included one-way ANOVA tests for 

 volume differences among eggs spawned in three subpe- 

 riods during the spawning season (initial, middle, and 

 final) in Valparaiso and Talcahuano (1996-97). We did 

 not have samples from the start of the spawning season 

 in 1996 for Valparaiso; thus, we used samples collected in 

 late June 1995 for this subperiod (Table 1). Variations in 

 the egg-size frequency distributions between contiguous 

 subperiods were also tested with nonparametric tests 

 (Kolmogorov-Smirnov test). Changes in egg volume with 

 latitude were tested by using egg sizes measured at four 

 localities (20°, 23°, 33°, and 36°S) during the peak spawn- 

 ing months (initial subperiod). The same statistical tests 

 were used as in the previous objective (ANOVA, Kolmogo- 

 rov-Smirnov test). 



To evaluate the relationship between egg size and lar- 

 val length at hatching, live eggs from ichthyoplankton 

 samples from the field in August 2000 were transported to 

 the laboratory and reared at the normal mixed-layer tem- 

 perature off Antofagasta and Talcahuano (15°C and 12°C, 

 respectively) (Escribano et al., 1995; Castro et al., 2000). 

 A subsample of the incubated egg batch was preserved in 

 5% formalin and measured at the beginning of the experi- 

 ments. The rest of the eggs were placed in 1-L flasks and 

 incubated until hatching under 12h/12h photoperiod. This 

 procedure was repeated twice (4 days apart) in each zone. 

 From each rearing experiment, 30 just-hatched larvae 

 (max. 30 min from hatch) were anesthetized and measured 

 (notochord length) under a dissecting microscope with the 

 aid of an ocular micrometer. Additionally, yolksac sizes of 

 recently hatched larvae were measured and volume esti- 

 mated as one half of an ellipsoid by using the algorithms 

 given above. 



Results 



A total of 7196 anchovy eggs were measured. The egg size 

 tended to decrease as the spawning season progressed 

 (Fig. 2). From late June through January the mean 

 volume decreased by about 20% in Valparaiso and by 

 about 10"% in Talcahuano (ANOVA, P<0.05)( Table 1). The 

 size-frequency distribution between consecutive subperi- 

 ods (initial, middle, and final) also differed in both areas 

 (Kolmogorov-Smirnov test, P<0.05). The mean size of the 

 eggs in Valparaiso was smaller than in Talcahuano during 

 all subperiods (Table 1 ), and the largest difference between 

 areas was at the end of the spawning season ( 15% ). 



During the spawning peak (spawning commencement ). 

 when the eggs were larger, the mean anchoveta egg size in- 

 creased with latitude (ANOVA, P<0.01; Fig. 3). At Iquique 

 (20"S), the mean egg volume was 21% smaller than at An- 

 tofagasta (23°S), 49% smaller than at Valparaiso (33°S), 

 and 5695 smaller than the eggs from Talcahuano (36°S), 

 the southernmost location (Table 2). The egg-size fre- 

 quency distribution differed between adjacent areas (Kol- 

 mogorov-Smirnov test. P<0.05). Interestingly, the smallest 



Pacific Ocean 



> 



73 

 Longitude West 



Figure 1 



Areas where anchoveta eggs were collected to 

 determine egg-size variations along the Chil- 

 ean coast. Arrows show the locations depicted 

 in Table 2. 



egg sizes measured in Iquique (<0.19 mm 3 ) did not occur 

 in Talcahuano. Similarly, the largest sizes determined in 

 Talcahuano (>0.30 mm 3 ) did not occur in Iquique. at the 

 lowest latitude. 



Larval length at hatching determined in the rearing 

 experiments at normal field temperatures was greater for 

 the southernmost population (Talcahuano) (Table 3). The 

 mean larval size for the southern location (2.70 mm noto- 

 chord length) was 8.2% greater than the larvae hatched 

 from eggs collected at the northern experimental location 

 (Antofagasta, 2.50 mm). Furthermore, the yolksac volume 

 in the recently hatched larvae in Talcahuano (0.130 mm 3 ) 



