THEILACKER: FEEDING AND GROWTH OF NORTHERN ANCHOVY 



Table 2.— Estimates ot the asymptotic gut contents (C^^) and in- 

 stantaneous rate of gut filling (k) for northern anchovy (n) fed 

 several diets'. 



'Includes zero gut contents; observed gut contents c at time t = C^^ x 

 (1 - e-"). 



^Prey width not measured. 



387% rotifers <150 ^m width. 



*Flsh eating Gymnodinium exclusively were removed to estimate C^^ and 

 k. 



sCopepod concentration <0.1/mL. 



the curves and dividing by the 12-h feeding period. 



Equations were derived for each diet from the 

 relation of C^ax and k with fish size and duration of 

 feeding; these equations allow the calculation of gut 

 contents c at time t for all fish lengths between 4 

 and 8 mm. The parameters (Table 3) were found 

 using the derivative-free nonlinear regression pro- 

 gram (BMDPAR) by Biomedical Computer Pro- 

 grams (BMDP, 1981). 



Daily consumption F^, was estimated using a 

 modification of an equation for consumption devel- 

 oped by Stauffer (1973) and discussed by Elliott and 

 Persson (1978) and Jobling (1981), F^ = rt + Cjg, 

 where r is the /ug evacuated per hour calculated as 

 mean gut contents c divided by the empirically 

 determined rate of gastric evacuation (see Evacua- 

 tion Rates), t is the duration of feeding, and C12 is 

 the dry weight of the food remaining in the stomach 

 at the end of the 12-h feeding period. 



Growth 



Length data for all feeding treatments were fit 

 to exponential growth curves, SL = Iqb''^ where ^0 

 is length at hatching, k is the instantaneous growth 

 rate and t is the age. Length-weight data were fit 

 to a power equation where weight W = a(SL)''; 

 parameters for the growth equations are given in 

 Table 4. 



Table 3. — Parameters for equation' relating observed gut contents c in ^^ g dry weight 

 at time t to standard length (SL) of northern anchovy fed three diets. 



Diet 



Age n 



(SD) 



(SD) 



(SD) 



"=0.69 



0.33 



0.326 



, PjSLd-e 



-(p, +P2-SL)(/) 



(SD) 



Rotifers 

 25/mL 5-14 280 -1.90 (0.70) 0.51 (0.18) 0.57 (0.16) 0.29 (0.03) 



2/mL 5-14 103 — — 



Copepods 



2/mL 5-9 171 2.84 (0.88) -0.39 (0.12) ^1.26 ^(0.75) 1.18 (0.10) 



'c = p^e' 



2(P, + Pj) fixed at 0.69, the mean k from Table 2; asymptotic standard deviations could not be 

 computed because k was held constant. 

 3x 10'^ 



Table 4.— Parameters for northern anchovy growth equations where SL is standard 

 length in mm, W is weight in /jg, and t is age in days. 



Diet 



Age 

 (d) 



Age length 

 SL = /o©*' 



Length-weight 

 W = a(SL)'' 



In 



(SD) 



(SD) 



(SD) 



(SD) 



Rotifers 

 25/mL 5-14 280 3.06 0.05 0.06 0.001 253 0.197 0.040 3.16 0.11 



2/mL 5-14 103 3.14 0.07 0.05 0.002 84 0.379 0.030 2.80 0.04 

 Copepods 



2/mL 5-9 138 3.06 0.15 0.07 0.010 109 0.297 0.097 2.88 0.20 



215 



