HUNTER and ROE; THE SPAWNING ENERGETICS OF NORTHERN ANCHOVY 



Table 6. — Calories gained per day and daily ration of two groups of northern anchovy fed 



Oregon Moist Trout Pellets. 



Group 



Standard length 

 (mm) 



Fat-free dry weight 

 (without ovary) (g) 



Fat in body 

 (without ovary) (g) 



Ovary dry 

 (Including 



weight 

 fat) (g) 



Duration of 

 experiment (d) 



Daily ration 2 

 (cal) 



Body (less ovary) 

 (fat free) 



Fat 



Ovary 

 (including fat) 



2 69 



3 78 

 Mean 73.5 

 Percentage of ration 



2,238 

 2,245 

 2.241 



53 

 60 

 56 

 2.5 



199 

 218 

 208 

 9.2 



19.8 



24.9 



22.4 



1.0 



' Caloric values in Table 2. 



^Method of calculation of ration outlined in methods. 



Total 



271 

 303 

 287 

 12.8 



Fat stores (F) are included in calculation of C in 

 the laboratory work (Equation (8)) but not in the 

 ration for natural populations (Equation (9)) be- 

 cause on an annual basis it is assumed to be 

 subsumed in the annual cost of reproduction. The 

 caloric value used for growth was set at the 

 minimum fat content of the year (15.4% of the dry 

 weight) using values in Table 2 and Equation (1). 



Laboratory Growth Efficiency 



most advanced batch in the ovary increased from 

 0.55 to 0.63 mm in group 2 and from < 0.25 to 0.63 

 mm for group 3. Most of the caloric gain was in fat; 

 the percentage of the dry weight that contained fat 

 increased from 32.6 to 44.2% in group 2 and from 

 24.5 to 43.2% in group 3 and accounted for about 

 9.2% of the daily ration. The caloric conversion 

 efficiency for the total gain of calories in the body 

 (including ovary and fat) was 12.8%. We calcu- 

 lated from data of Takahashi and Hatanaka ( 1960) 



Northern anchovy (groups 2 and 3) maintained 

 in the laboratory grew much faster than those in 

 the sea. The growth in length was about four times 

 that estimated for wild northern anchovy by 

 Spratt (1975) but was seven times faster when 

 Spratt's data were converted to wet weight using 

 the length-weight conversion for females of 

 Collins (1969) (solid line, Figure 9). Thus, the 

 average ration consumed by northern anchovy in 

 the laboratory, 2,241 cal/d (about 124 cal/g fish wet 

 weight per d) is probably much larger than the one 

 consumed in the sea. On a wet weight basis, the 

 laboratory ration (4.5% of fish wet weight/d) is 

 deceptively low because the pelleted food had a 

 much lower water content (35%) than natural 

 foods (85%). A caloric equivalent ration of natural 

 foods (copepods) would be about 16% of the wet 

 weight/d. 



Spawning did not begin during the experiment, 

 hence the proportion of the daily ration incor- 

 porated into the ovaries (0.8%) was a function of 

 only maturation of the ovary (Table 6). The 

 median of the mean major axis of the eggs in the 



24 r 



22 



CT 



K 20 



I 

 o 



UJ 



3 18 



t- 



LJ 



> 



o 



X 



o 14 - 

 < 



12 - 



10- 



1.5 



DAYS IN LAB 



O GROUP 2 



• GROUP 3 



— Years in sea 

 (Sprott 1975) 



O 



ELAPSED TIME IN LABORATORY (days) 



J I I I I 1 1 1 



20 



30 



40 



50 



60 



70 



80 



J I I I I I I I L 



2.0 



2.5 

 YEARS IN SEA 



3.0 



J I 



3.5 



Figure 9. — Growth in days of two groups of northern anchovy 

 in the laboratory (dots and circles) compared with the growth 

 over years of northern anchovy in the sea (solid line). Growth in 

 the laboratory is plotted using upper scale (elapsed time days), 

 and growth in sea (solid line, from Spratt 1975; Collins 1969) is 

 plotted on lower scale (years); and ratio between scales is about 

 1:7. Each point is mean weight for 8-12 fish. Laboratory fish were 

 fed a pelleted trout ration which was the caloric equivalent in 

 natural foods of about 16% of the fish wet weight per day. 



225 



