NOTE Olson and Scholey Growth of late-larval and early-juvenile Eu:hynnus hneatus 



825 



8 10 12 14 16 18 



ESTIMATED STANDARD LENGTH AT CAPTURE (K*i) 



0.024 0-040 0.056 0.072 0.088 



ESTIMATED WEIGHT AT CAPTURE (G) 



Figure 4 



Standard lengths estimated in tlie lalxiratory and weiglits calculated 

 fr(ini a weight-length regression (Fig. 6) for 39 black skipjack tuna 

 held for growth experiments. 



tions. Water temperature and salinity in the laboratory 

 aquaria ranged from 23.7 to 29. TC and 29 to 34"A.o, 

 respectively, over all the experiments. 



Growth in length 



Captive black skipjack fed ml libitum grew in a curvi- 

 linear relationship of SL with time (Fig. 5a). The data 

 were not fitted to derive a predictive growth equation 

 because they are inadequate for that purpose. The fish 

 were fed to satiation, but the rations were not 

 measured. 



The highest rates of growth in length were attained 

 during the first month in captivity (Fig. 5b). After 

 about 4 weeks, the fish had progressively lower aver- 

 age growth rates. Black skipjack from experiments 

 that terminated during the first 15 days of captivity 

 grew at extremely variable rates, from 1.0 to 4.8 

 mm/day. After 15 days, there was a significant nega- 

 tive correlation between growth rate and days in cap- 

 tivity (r = -0.877, n = 23, P«0.001). All the fish that 

 survived between 15 and 50 days grew rapidly, 3.2-4.8 

 mm/day. After about 50 days in captivity average 

 growth rates declined drastically. 



Errors in estimating lengths of newly-captured fish 

 that had recently died or were near death in the tanks 

 soon after capture ranged up to ± 4 mm, although most 



Figure 5 



Standard lengths (a), growth rates in standard length averaged over 

 the duration of captivity (b), weights (c), and growth rates in weight 

 averaged over the duration of captivity (d) of juvenile black skip- 

 jack tuna at the end of laboratory growth experiments versus days 

 in captivity. Two fish held 1 1 days were not weighed. 



were less. Maximum potential errors in growth rates 

 were calculated based on the assumption that ± 4-mm 

 errors were made when estimating capture lengths of 

 all the experimental fish. In general, the importance 

 of measurement error diminished with increasing time 

 in captivity. Potential errors ranged from only ±0.8 

 to a high of ±53.3% for one fish held the least time 

 of all experimental fish (7.5 days). The next greatest 

 error estimates were -26.1 and -i-23.8%, and the 

 means were ±8.8%. Potential errors for the majority 

 (85%) of the samples were ± 13.5% or less, and less 

 than 10% for all fish held in captivity more than 15 days 

 (n = 2b). 



Growth in weight 



Growth in weight appeared to follow a sigmoidal rela- 

 tionship with time in captivity (Fig. 5c). The rate of 

 weight gain during the first 30 days was low, increas- 

 ing dramatically between about 30 and 70 days, and 

 then tapering off after 70 days. 



While the greatest and most variable growth rates 

 in length took place during the first 30 days, average 

 rates of weight gain during that period were less than 



