HUNTER and ROE: THE SPAWNING ENERGETICS OF NORTHERN ANCHOVY 



at 7-10 d intervals occurs in the laboratory and 

 could occur in the sea. In addition, the forms of 

 the theoretical and the laboratory maturation 

 curves were similar, with maturation of small 

 unyolked eggs being much slower than that of 

 larger yolked eggs. 



Cessation of Spawning 



An assumption of some fecundity studies of 

 multiple spawning fishes is that all eggs to be 

 spawned in a season are yolked at the beginning of 

 the season and spawning ends when these yolked 

 eggs are depleted. The preceding analysis indi- 

 cated that yolking of eggs from the reservoir of 

 small unyolked eggs is a continuous process in 

 northern anchovy. In this section we determined 

 whether spawning ceases because of a lack of eggs 

 of an appropriate size for maturation. We com- 

 pared egg size-frequency distributions from six 

 females with highly atretic ovaries with those 

 of reproductively active females. Although the 

 ovaries of the six females contained yolked eggs, 

 they were highly atretic and judged to be in post- 

 spawning condition, using histological criteria 

 presented by Hunter and Macewicz (1980). 



The form of the line relating the mean major 

 axis of eggs to successive spawning batches 

 (dashed line, Figure 4, upper) was similar in form 

 to those of the other groups. The eggs in the most 

 advanced spawning batch were smaller (0.45 mm) 

 in atretic ovaries than in those of females that had 

 spawned 24 h before capture (0.55 mm). Hunter 

 and Goldberg (1980) showed that the mean major 

 axis of the most advanced eggs (excluding 

 hydrated eggs) was 0.46 mm in females captured 

 on the night of spawning. This value is very close 

 to the mean for highly atretic ovaries. Thus, 

 oocyte maturation, at least in these six females, 

 probably continued up to the time of the last 

 spawTiing, whereupon maturation ceased and the 



remaining oocytes became atretic. Spawning did 

 not cease because of lack of yolked eggs; the atretic 

 ovaries of these six females had the same dis- 

 tribution of egg sizes as any female ovary imme- 

 diately after spawning. 



ENERGY COST OF SPAWNING 



We consider here three variables affecting the 

 cost of reproduction: Number of eggs in a spawning 

 batch, size of eggs, and the energy existing in a 

 mature ovary. Factors not considered include the 

 metabolic costs of egg maturation and reproduc- 

 tive behavior and variation in the caloric content 

 of eggs. 



Number of Eggs 



The spawning batch fecundity (number of hy- 

 drated eggs) of northern anchovy varies exponen- 

 tially with female weight (Equation (4) ). Similar 

 to many other fishes (Bagenal 1973), fecundity 

 among females of the same size or weight is highly 

 variable. Variability may be caused by variations 

 in egg size, food availability, and number of 

 previous spawnings within the season. 



Feeding conditions may not greatly affect batch 

 fecundity in northern anchovy. Females matured 

 in the laboratory (groups 2 and 3) were fed a high 

 ration and grew about four times faster than 

 those in the sea, yet the batch fecundity was about 

 the same as field-caught specimens, which con- 

 sume a lower ration (Table 3). Although the 

 laboratory females had not begun spawning, their 

 batch fecundity was similar to that offish taken in 

 the sea between January and April. This indicates 

 that the average batch fecundity may not change 

 over the first months of spawning. The fact that 

 fecundity of females captured in March- April 1979 

 was about the same as that for January-February 

 1979 (Hunter and Macewicz 1980) also supports 



Table 3. — Comparison of the batch fecundity of northern anchovy females matured in laboratory and in the 



sea within two weight classes. 



'From Equation (4) (Hunter and Macewicz 1980); intercept increased by 0.0647 ('/js^) to adjust for bias in taking antilog (Beau- 

 champ and Olson 1973). 



^Batch fecundity = number eggs in most advanced mode in ovary where mean egg size 5=0.65 mm (major axis; eggs not hydrated). 



^Batch fecundity = number of hydrated eggs In females without new postovulatory follicles (Hunter and Goldberg 1980; Hunter 

 and Macewicz 1980). 



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