FISHERY BULLETIN: VOL. 74, NO. 1 



were fed with frozen and live brine shrimp, 

 Artemia sp., under variable regimes as described 

 below. Each experimental population of nehu was 

 sampled during placement in holding tanks, and 

 then subsampled at various time intervals as 

 described for each experiment. Otoliths were ex- 

 tracted from most specimens within a few hours of 

 sampling. The remaining samples were frozen in 

 seawater or preserved in 75% solution of iso- 

 propanol until extraction of otoliths (removal of 

 tissue from otoliths of alcohol preserved speci- 

 mens is difficult). 



The first holding experiment was begun 5 

 April 1972. A 16-day sample (21 April) and a 

 34-day sample (9 May) were obtained from 

 this population. The animals were fed once a 

 day With frozen and/or live brine shrimp. The 

 second holding experiment was begun 15 Decem- 

 ber 1972. This population was initially fed once a 

 day. A high mortality was observed during the 

 first 2 wk, after which food was provided twice 

 daily. Samples were collected weekly after 1 mo of 

 captivity. We examined sagittae from animals 

 collected on 19 January and 26 January 1973. The 

 third holding experiment was begun 4 May 1973. 

 This population was fed two or three times daily 

 with frozen brine shrimp. Samples were obtained 

 weekly between 4 May and 6 July. We examined 

 sagittae from animals collected 25 May and 8 

 June 1973. 



Wild populations of larval, juvenile, and adult 

 nehu were sampled 13 times in Kaneohe Bay be- 

 tween 19 March 1972 and 13 July 1973 to obtain 

 estimates of growth rates at various seasons. Al- 

 though a second species of Stolephorus (S. buc- 

 caneeri Strasburg) occurs in Hawaii, larvae of this 

 species have not yet been collected in the south- 

 eastern end of Kaneohe Bay (Watson and Leis 

 1974; W. Watson pers. commun.). 



After extraction, the sagittae were cleaned and 

 etched for up to 3 min in a 1% solution of HCl, then 

 washed and mounted whole on glass slides with 

 the mounting medium EuparaP and covered with 

 glass cover slips. Short lengths of monofilament 

 line were used to prevent the contact of the 

 specimen by the cover slide. Although the small- 

 est growth increments are microscopically dis- 

 cernible immediately after extraction their detec- 

 tion was enhanced after about 30 days of clearing 

 in the mounting medium. Sagittae used in the 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



first holding experiment and those collected from 

 Kaneohe Bay and Pearl Harbor during spring 

 1972 were placed in glycerine on slides and 

 covered. Some erosion of the sagittae edges was 

 noted after about 5 mo, and this practice was 

 discontinued after the first experiment. Slides 

 were either labeled with date of collection and 

 length of fish or assigned a five digit random 

 number for identification. 



Our initial counts were taken from thin sections 

 of sagittae taken on the frontal plane. After 

 mounting the sagittae in epoxy resin, the initial 

 plane of polishing was made with rough sand- 

 paper. As the surface approached the desired 

 section, fine wet silicon carbide sandpaper (400 

 grit) was used. Final polishing of the surface was 

 done with suspensions of aluminum oxide parti- 

 cles having diameters of 15, 5, and 0.3 /^m. The 

 section was thinned on the opposite side to a 

 practical thickness and etched in a 1% solution of 

 HCl for variable periods up to 3 min. A few 

 attempts to make acetate peels of the small nehu 

 sagittae sections as described by Pannella (1971) 

 and Pannella and MacClintock (1968) were un- 

 successful. We eventually abandoned the section- 

 ing of sagittae because of the time required and 

 the difficulty in obtaining a precise section from 

 the nucleus to the posterior edge of the sagitta. 



Sagittae were obtained from larvae less than 

 about 20 mm SL by placing the specimen on a slide 

 and gently teasing the otoliths from the head re- 

 gion. The sagittae were then mounted in Euparal 

 and read immediately. These otoliths tended to 

 clear completely within a few hours, and photo- 

 graphs are the only permanent record of these 

 specimens. 



The smallest growth increments of the mounted 

 sagittae were counted with a compound micro- 

 scope at magnifications of 400-800 x . The smallest 

 growth increment in all fish otoliths consists of 

 both an organic and an inorganic layer (Degens et 

 al. 1969). These two layers in the nehu otolith to- 

 gether measure about 1-4 ^im thick. A zoom fea- 

 ture of the microscope was found to be extremely 

 useful. Counts were maintained on a hand tally. 



Enumeration of the smallest growth increment 

 layers in whole sagittae is tedious, and reliable 

 counts can be obtained only after a moderate 

 amount of experience has been acquired. Enu- 

 meration is, obviously, much easier in sagittae 

 from smaller fishes (Figure 1). Usually, readings 

 cannot be made in a direct line from the nucleus to 

 the selected point on the edge of the sagitta; 



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