FISHERY BULLETIN: VOL. 72. NO. 2 



ascending arm of the preoperculum increased 

 from two (2.9-3.5 mm larvae) to as many as 

 six (7.0-9.0 mm larvae) and from two to seven 

 along the anteriorly projecting descending arm. 

 The apical spine of the preoperculum remained 

 slightly larger and broader-based than the others 

 as in the jack mackerel (Ahlstrom and Ball, 

 1954), but was still smaller and less prominent 

 than in our other common carangid larva, 

 Gnathanodon speciosus (unpublished data), and 

 provides one characteristic for separating the two 

 species. 



The omaka larvae showed no serrated dorsal 

 crest at the back of the head which was evident 

 in the jack mackerel (Ahlstrom and Ball, 1954). 

 It is considered to be a rather common feature 

 of carangid larvae (Berry 1959, McKenney, 

 Alexander, and Voss 1958, Okiyama 1970, Sho- 

 jima 1962) and is present in several of our 

 unidentified species of carangid larvae. 



GROWTH 



The growth rate and description of changes in 

 body form are based mainly on specimens reared 

 from eggs taken in surface tows from Kaneohe 

 Bay on 22 February 1971 (Table 1). At that time 

 the bay surface temperature was 24.4°C. Rearing 

 tank temperatures ranged from 22.1° to 25.9°C, 

 with a mean of 24.5°C, so the thermal environ- 

 ments were similar. As stated in the methods 

 section, the salinity and oxygen level in the tank 

 remained similar to those in the bay throughout 

 the experiment. Without data on the quantity 

 and quality of food for any given time of the 

 rearing period, however, it is impossible to assess 

 the reality of the growth rate. The general shape 

 of the curve (a nearly straight line) and the 

 absence of any mass mortality suggests that the 

 rearing environment was at least adequate 

 throughout the experiment. The absence of 

 prolonged lags in growth suggest the absence of 

 periods of major stress. 



The growth curve (Figure 4) is composed of at 

 least three segments of differing slope: from 

 hatching through day 2; day 3 through day 5; and 

 from day 6 onward. The inflection in the curve 

 at day 2-3 coincides with the near final absorp- 

 tion of yolk, and perhaps more important, the 

 development of a functional mouth. No major 

 structural change occurs at day 6 which might be 

 linked to that inflection. Among four rearing 





o 



z 



z 



Y^-0 3016 ♦0.4362 X 



r. 0.9929 



n.16 



16 20 



TIME (DAYS) 



28 



32 



Figure 4. — Growth rate oiCaranx mate in culture. Regression 

 based on mean length after day 6. n = 16. 



trials, the change in length from hatching to day 6 

 (ca. 2.5 mm) was extremely variable. In two of 

 the trials, larvae increased in length through 

 day 3, then shrank. It appears that the vari- 

 ability in early omaka growth rate might be 

 linked to the success of larvae in obtaining their 

 first exogenous energy (Thomas Cooney, pers. 

 comm. — M.A. thesis research). Owing to this 

 variability, the statistical description of the 

 growth rate of larvae through day 5 is of little 

 value. Interpolation between mean (preserved) 

 size at hatching (1.03 mm) and mean size of day 6 

 (3.05 mm) yields an estimate growth of 0.35 

 mm/day. 



The relationship chosen to express larval 

 growth beyond day 6 was the linear regression: 

 SL (in mm) = -0.3016 + 0.4362 (age in days) 

 (Figure 4), as determined from 153 preserved 

 specimens. A slightly better fit would have been 

 obtained with a more complex function, but the 

 improvement in the curve would be slight. 



The greatest departures from linear growth 

 occurred at day 14 and day 28 (SL = 5.2 mm and 

 11.4 mm, respectively). No major morphological 

 developments occurred at these sizes, so the 

 causes (if the departures are real) are not known. 

 The generally poorer fit of the data to the curve 

 at the largest sizes is probably attributable to 

 sampling. As the vagility of larvae increases with 

 size, the probability increases that the smaller 



510 



