Headlight Fish

Diaphus effulgens

This bipolar subtropical species (Backus et al., 1977) is known to exceed 150 mm in length (Nafpaktitis et al., 1977). The largest specimen caught during Ocean Acre was 96 mm. Diaphus effulgens was uncommon in the study area at all seasons. The Ocean Acre collections contain 120 specimens; 51 were caught during the paired seasonal cruises, 36 of these in discrete-depth samples, of which 30 of the latter were in discrete-depth noncrepuscular tows (Table 23).

DEVELOPMENTAL STAGES.—Juveniles were 12–58 mm, subadults 53–63 mm, and adult males 77–90 mm. Adult females were not taken. Juveniles smaller than 50 mm could not be sexed. The eight largest fish (69–96 mm) were males, and the largest female was 63 mm. This apparently is not a reflection of a sexual dimorphism in size, as Nafpaktitis et al. (1977) examined females up to 139 mm.

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—The reproductive cycle and life span of D. effulgens in the study area is uncertain. Based upon the relatively large size attained, this species probably lives at least two years. The parent population probably breeds in spring and summer, with a peak in late spring. Abundance, although quite low at all times, is at a maximum in late summer (Table 45).

Recruitment of small fish (less than 20 mm) occurred only in August and September, at which time they made up more than 80 percent of the total number taken in both nondiscrete and discrete-depth samples. Adult males were caught only from June to September. The seasonal distributions of small juveniles and adult males suggest that spawning occurs in spring and summer.

In winter and late spring fish larger than 40 mm predominate, and abundance is about half that in late summer (Table 45). In late summer fish smaller than 20 mm dominated the discrete-depth collections. At that season the combined IKMT and Engel trawl catches apparently consisted of at least three year classes: young-of-the-year fish, 12–23 mm (taken only in the IKMT); fish about one-year old, 35–59 mm; and fish two or more years old, 80–92 mm. Fish of the latter two groups, with one exception, were taken with the Engel trawl.

VERTICAL DISTRIBUTION.—Vertical distribution for all seasons combined was by day, 501–700 m; and by night, 90–200 m. By day, fish taken at 501–600 m were 14–33 mm and those at 601–700 m depths were 40–86 mm; at night all but one fish 40 mm and smaller were taken at 90–100 m, with larger fish near or below 150 m. During both day and night juveniles were found throughout the vertical range; the more advanced stages were only at or near the lower depth limit (Table 46).