THEILACKER: FEEDING AND GROWTH OF NORTHERN ANCHOVY 



(/) 



5.25 



•" 1.50 2" 3.00 3" ,50 5.25^^0 6.75 ^ ^^ 



TIME (hours) 



Figure 2.— Observed stomach contents of 4.0-4.5 mm northern 

 anchovy fed 25 rotifers/mL, predicted rate of gut filling k and 

 predicted maximum gut content C^^. Each point is one larva. 



Table 8. — Mean dry weight of food (^g) observed in stomachs' of 

 northern anchovy (n) related to their age. 



■> Average stomach contents (excludes empty stomachs) calculated for f = 

 >3 hours; 3 hours is a reasonable time for northern anchovy to fill guts eating 

 at lowest prey densities tested (see text). 



2Day 13. 



tion for northern anchovy was curviUnear on a log- 

 log plot, and he used a Laird Gompertz model to 

 describe both growth in length and in weight over 

 75 days. Because I am describing only the first 2 

 weeks of growth, I used a simpler exponential model 

 (Table 4) which probably should not be used for lar- 

 vae beyond 2 weeks of age. 



Larvae grew at 0.35 mm/day on the copepod diet 

 {k = 0.07) and at 0.33 and 0.25 mm/day on the high- 

 {k = 0.06) and low-density (A; = 0.05) rotifer diets 

 (Table 4). On the average, the dry weight of larval 

 northern anchovy was proportional to length to the 

 third power. Depending on diet, the length exponent 

 ranged from 2.80 to 3.16 (Table 4). 



Daily percent increases in dry weight for northern 

 anchovy fed the rotifer diets were 15% for larvae 

 fed 2/mL and 21% for larvae fed 25/mL. However, 

 northern anchovy grew the most, 23% per day, on 

 the 2/mL copepod diet. For the three diets tested, 

 daily growth in dry weight as a percent was con- 

 stant over the size range. 



An analysis of covariance was used to test for diet- 

 induced differences in the relation between natural 

 logarithms of length and weight for larval northern 

 anchovy between days 5 and 9 when prey concen- 

 trations were controlled. Larvae which fed on cope- 

 pods were significantly longer and heavier at age 

 than larvae eating rotifers. There were no length 

 or weight differences at age 7 days between the two 

 rotifer treatments (Table 9), but there were differ- 

 ences in growth thereafter. Larvae raised on the two 

 rotifer diets were the same weight at 4.9 mm (30.75 

 and 33.25 yig; P = 0.3), but larvae raised on cope- 

 pods weighed less at 4.9 mm (28.54 ^g) than larvae 

 fed on the rotifer diets (P = 0.11 and <0.01). 



I compared the distribution of my northern an- 

 chovy dry weights at length for the rotifer and 



Table 9. — Effect of diet on northern anchovy standard length (SL) and dry weight {W). 



Age = 



7 days 



Probabilities 



= SL and = W 



'Case numbers contain 2-12 larvae depending on number in group that were weighed. 



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