HUNTER and ROE: THE SPAWNING ENERGETICS OF NORTHERN ANCHOVY 



Macewicz 1980), resulting in a rapid increase in 

 ovary wet weight (Figure 7, lower) but no change 

 in dry weight (Le Clus 1979). The mean size of eggs 

 in a spawning batch, just before hydration, ranges 

 from 0.6 to 0.8 mm; eggs >0.8 mm nearly always 

 show histological signs of hydration. The average 

 size of eggs that are hydrated would be expected to 

 vary since the size of spawned eggs is variable. 



The wet weight of the ovary (G) increases 

 during maturation and is a function of the mean 

 major axis of the eggs in the most mature spawn- 

 ing batch (M) and female wet weight without 

 ovary (W); in northern anchovy this function is 

 expressed as 



\ogc G = -4.213 + 1.069 logc W 



+ 0.555 M log, W (6) 



1980). The spawning batch of a 16.4 g female 

 contains 6,500 eggs or 1,066 cal (from Equation 

 (4)1. Thus, just before spawning the ovary con- 

 tains about 2,059 cal and the most advanced 

 spawning batch constitutes about 52% of the 

 calories in the ovary (documentation given in 

 Table 4). Similar calculations can be made using 

 the volume of eggs in the ovary and egg dimen- 

 sions given in Figure 7 (upper) or by calculating 

 the wet weight of the ovary at 0.46 mm egg major 

 axis (after spawning) and at 0.81 mm egg major 

 axis (at onset of hydration) using Equation (6). All 

 calculations yield similar results when converted 

 to dry weight or calories, i.e., about one-half of the 

 calories in the ovary are lost in one spawning. We 

 conclude that the calories invested in a mature 

 ovary are small relative to the total reproductive 

 cost of 20 spawnings. 



(Hunter and Goldberg 1980) (Figure 7, lower). The 

 water content of the ovary of laboratory females 

 (group 1) declined during maturation from 80 to 

 659c just before hydration (Figure 7, center). 

 The fat content did not change significantly over 

 the maturation period; mean ovarian fat content 

 of laboratory-matured northern anchovy was 

 18.6 ±1.2% (±2 SE of mean, n = 41) of ovary dry 

 weight. As the fat content did not change, the 

 caloric value of ovarian tissue can be considered to 

 be constant at 5,710 cal/g dry weight (Table 2). 



Using Equation (6), caloric values (Table 2), and 

 water content of ovary (Figure 7), we estimate the 

 ovary of a 16.4 g female contains 933 cal just after 

 spawning when the mean major axis of most 

 advanced eggs = 0.46 mm (Hunter and Goldberg 



ANNUAL FAT CYCLE AND SPAWNING 



As the caloric equivalent of only two spawnings 

 exists in the ovary at one time, northern anchovy 

 must use energy stored in other tissues and food 

 income to support reproduction. Lasker and Smith 

 (1977) showed that the fat content of northern 

 anchovy, like many other clupeoids (Blaxter and 

 HoUiday 1963; Shul'man 1974) varies seasonally. 

 The fat accumulates in the body rapidly between 

 April and July, matching the annual spring bloom 

 of zooplankton (Lasker and Smith 1977). It usually 

 remains high through December and then de- 

 clines to a minimum between February and May 

 (Figure 8). The decline in fat occurs during the 

 months of maximum spawning. Thus, fat stored 



Table 4. — Reproductive characteristics for the average female northern anchovy. 



Item 



Value 



Explanation and data source 



Weight and fecundity: 



For 1978 and 1979 (Hunter and Macewicz 1980) 

 Equation (6) where M = 0.46 mm 

 Percentage water in ovary from Figure 7 (center) 

 Equation (4) 



Assume 20 spawnings (Figure 2) 



Mean of monthly dry weight: (Figure 6) weighted by relative 

 monthly larval abundance (Lasker and Smith 1977) 



Caloric value of eggs = 5,450 cal/g (Table 2) 

 Caloric value of ovary = 5,710 cal/g (Table 2) 



Assume spawning interval = 7 d 



Equation (1) where 41% of dry weight = fat 

 Equation (1) where 15°o of dry weight = fat 

 Caloric value of fat = 9,227 cal/g (Table 2) 



' Females with postovulatory follicles < 24 h old. 



223 



