Sudekum et a\ : Life history and ecology of Caranx ignobilis and Caranx melampygus 



495 



sagittae were clearly evident in this dissection. Otoliths 

 were removed from each side of the cranial cavity, 

 cleaned, washed, stored in glycerol, then dried at 60 °C 

 for 24 hours, and weighed. Right and left otoliths were 

 segregated. 



Whole sagittae were embedded in epoxy casting resin 

 and serially sectioned with a low-speed jewelers' saw. 

 Sections 300 ^m thick were attached to scanning elec- 

 tron microscope (SEM) viewing stubs with 5-min epoxy 

 and polished with 0.3/^m alumina paste. The polished 

 sections were etched for 1-20 minutes with 6% 

 ethylene diamine tetraacetate (EDTA) with pH ad- 

 justed to 8 with sodium hydroxide. The otolith sections 

 were washed in water, dried, coated with gold, and 

 viewed in an SEM at various magnifications. 



A sample of five right sagittae were sectioned in dif- 

 ferent planes as described by Radtke (1987) to deter- 

 mine that the optimum plane for enumerating incre- 

 ments was the transverse frontal plane. With this 

 technique, we believe that no increments were lost in 

 the chosen plane. Smallest increments were counted 

 with the SEM on sections in this plane of the left sagit- 

 tae of all specimens used for age determination. In- 

 crements were counted from sequential SEM images 

 of the otolith surface, starting at the origin (center) and 

 moving to the otolith margin at the rostrum (anterior). 

 With this methodology, the area read for ageing was 

 consistent for all individuals analyzed. On the assump- 

 tion that one increment equals one day's growth (Pan- 

 nella 1971 and 1974), the data were fitted to the von 

 Bertalanffy growth equation (Fabens 1965). 



A marking study using tetracycline was undertaken 

 to validate the assumption of daily periodicity of otolith 

 increments. Live carangids were collected from Kane- 

 ohe Bay, Hawaii by commercial fishermen using bait 

 nets. Six juvenile C. melampygus (197-338 mm SL) and 

 four juvenile C. ignobilis (113-225mm SL) were ac- 

 climated for 1 month in a tank of flowing seawater 



5.5m in diameter by 0.6m deep, exposed to natural 

 sunlight. After 1 month, the fish were measured and 

 given an intraperitoneal injection of 27.5mg/kg wet 

 body weight of oxytetracycline. To reduce trauma to 

 the fish, they were not weighed at the time of the in- 

 jections, but their weights were estimated from length- 

 weight relationships derived from wild-caught fish 

 (Table 1). The fish were fed ad libitum on a diet of raw 

 herring until recapture, when they were sacrificed. 

 Five C. melampygus were sampled after 55 days, the 

 sixth C. melampygus and the four C. ignobilis after 137 

 days. Upon recapture, all fish were weighed and stan- 

 dard, fork, and total lengths were measured. 



Sagittae from all experimental fish were removed, 

 cleaned, dried, and mounted in clear casting resin. Sec- 

 tions were made both perpendicular and parallel to the 

 rostral axis of the otolith. The sections counted were 

 in a transverse frontal plane, much the same as those 

 prepared for the SEM and as described by Radtke 

 (1987). Sections were polished with 400-grit Carborun- 

 dum wet-dry sandpaper, mounted on glass slides, and 

 viewed at 300 x under a binocular microscope with an 

 ultraviolet light source. The number of increments be- 

 tween the fluorescent mark and the outside edge of the 

 otolith was counted and compared with the number of 

 days that the fish was alive after injection. 



Reproduction 



Sex ratio, spawning season, and size at first reproduc- 

 tion (SFR) were estimated for both species. Gonads 

 were visually examined and classified as male, female, 

 immature, or unknown. These classifications were 

 based on the size, color, morphology, and texture of 

 the gonadal tissue. Gonads from 70 C. melampygus and 

 10 C. ignobilis were removed, wet weighed to the 

 nearest gram, and kept frozen for later, more detailed 

 analysis. 



