Günther’s Lanternfish

Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.

Dorsal spines (total): 0; Dorsal soft rays (total): 13 - 15; Analspines: 0; Analsoft rays: 13 - 16

High-oceanic (Ref. 4066). Found between 425-750 m during the day and between 40-125 m at night (maximum abundance in the upper 50 m) (Ref. 4479). Feeding is acyclic in northwest Africa (Ref. 9198).

High-oceanic (Ref. 4066). Found between 425-750 m during the day and between 40-125 m at night (maximum abundance in the upper 50 m) (Ref. 4479). Feeding is acyclic in northwest Africa (Ref. 9198). Reach sexual maturity at 4.7 cm (Ref. 47377).

Lepidophanes guentheri

This moderately large species, which attains 78 mm elsewhere (Hulley, 1981), grows to 63 mm in the study area, but very few specimens were larger than 57 mm. Like its congener, L. gaussi, this species is restricted to the Atlantic Ocean, where it is an abundant tropical species (Nafpaktitis et al., 1977). According to Backus et al. (1977) L. guentheri is not common in the North Atlantic subtropical region; the Ocean Acre collections substantiate this. The species is uncommon in the study area and never was included among the 15 most abundant lanternfishes. The Ocean Acre collections contain 365 specimens; 109 were collected during the paired seasonal cruises, 74 of these in discrete-depth samples, of which 56 were caught in noncrepuscular tows (Table 23).

DEVELOPMENTAL STAGES.—Juveniles were 16–40 mm, subadults 38–60 mm, and adults 53–58 mm. Only two adults were caught; the smaller was a male and the larger a female. Most juveniles smaller than 25 mm could not be sexed; the few that could be were all females. All juveniles larger than 25 mm could be sexed. The adult female had some eggs as large as 0.4 mm but most were 0.2–0.3 mm in diameter. None of the other females examined contained eggs larger than 0.1 mm. No sexual dimorphism in size or in the distribution or amount of luminous tissue was apparent.

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—Lepidophanes guentheri apparently has little reproductive success near Bermuda, with only a very small portion of the population reaching sexual maturity. Recruitment of fish smaller than 20 mm occurred from June to January and was greatest in January, when they accounted for about half of the abundance. The life span cannot be determined, but judging from the moderately large size attained, it could be more than one year.

Although females of adult size, 47 mm or larger (Hulley, 1981, who observed one as small as 41 mm), were taken throughout the year, only one female with eggs larger than 0.1 mm in diameter was observed. The presence of this individual indicates that some spawning may occur in the study area, but the prolonged period of recruitment of fish smaller than 20 mm cannot be accounted for by a resident spawning population.

In winter juveniles accounted for most of the abundance, those 16–18 mm comprising more than 50 percent of the total abundance (Table 108). Otherwise, only subadults 43–52 mm were taken. All specimens caught in winter were either smaller than 30 mm or larger than 40 mm, with the smaller group being caught mostly at night in January and the larger mostly by day in February. This bimodal size frequency distribution was not evident at any other season.

In late spring, except for a 16 mm juvenile, all specimens were 34 mm or larger. Abundance was low, and no peaks were evident in the size frequency distribution.

Most sizes contributed to the increase in abundance from late spring to late summer, suggesting that recruitment may involve fish of all ages and not only recently spawned ones.

SEX RATIOS.—The sexes probably were equally abundant at all seasons. Females and males were caught in approximately equal numbers at each season, with female-to-male ratios of 1.2:1 in winter, 1.5:1 in late spring, and 1:1 in late summer. Neither these ratios or those for individual stages differed significantly from equality (Table 109).

VERTICAL DISTRIBUTION.—Daytime catches were very poor; at each of the three seasons only 2–4 specimens were caught. Depth ranges obtained from these catch data were 701–850 m in winter, 751–800 m in late spring, and 751–950 m in late summer (Table 110).

Except in late spring, when only two specimens were caught, night catches were much better. Depth range at night in winter was 50 m and 151–200 m with nearly the entire catch made at the latter depth, in late spring 50–100 m, and in late summer 51–150 m, 301–350 m, and 751–800 m with maximum abundance at 51–100 m (Table 110).

At night in late summer juveniles were most abundant at 51–100 m and subadults at 101–150 m. Juveniles were not caught at the latter depth. In terms of size, the catch at 51–100 m was 20–56 mm with a mean size of 36.0 mm, and that 101–150 m was 51–57 mm with a mean of 54.8 mm (Table 110).

An even finer stratification existed at 51–100 m. Only juveniles were caught above 90 m. At 90 m both juveniles and subadults were caught, the second being the more abundant stage. All specimens captured above 90 m were smaller than 30 mm, and the size range at 90 m was 26–56 mm.

Diel vertical migrations occurred at each of the three seasons. Only one specimen, a 56 mm subadult taken at 751–800 m in late summer, was caught at daytime depths at night (Table 110).

Little information concerning the chronology of daily vertical migrations is available. In late summer, depths intermediate between those of day and night were occupied by about 1.5 hours before sunset, and nighttime depths were reached no later than 1.5 hours after sunset. In both winter and late summer nocturnal depths were still occupied at about 1.0–1.5 hours before sunrise.

PATCHINESS.—Patchiness was indicated at night at 151–200 m in winter and 51–100 m in late summer. At night in winter L. guentheri apparently concentrates at or near 175 m. Within the 151–200 m interval only two of six samples were positive for the species; both were made at 175 m and each contained eight specimens, all juveniles. A third sample taken at 175 m immediately after the two positive ones failed to catch the species. However, this sample was taken near the morning crepuscular period, and migrations may have started by that time.

In late summer most of the variation in catch rates was from samples taken at 90 m. Samples from other depths within the 51–100 m interval caught one or two specimens. Most of the variation in catch size at 90 m was due to subadults; juveniles were distributed uniformly and apparently did not have a patchy distribution.

NIGHT:DAY CATCH RATIOS.—Night-to-day catch ratios, including interpolated values, were 1.2:1 in winter, 1.4:1 in late spring, and 3.4:1 in late summer (Table 111). Diel differences in the size composition of the catches suggest that most of the differences between day and night catches probably were the result of sampling deficiencies. The daytime catch in winter was 43–46 mm and in late summer 35–39 mm; at night the catches were 16–20 mm and 17–57 mm, respectively. These differences show that specimens taken in daytime samples from both seasons and night samples in winter do not adequately represent the population present at those times. The lack of specimens smaller than 30 mm in day samples indicates that incomplete depth coverage may have been at least partially responsbile for the observed inequities, as smaller fish were not likely to be more capable of avoiding the nets than larger fish. The patchiness noted at night at both seasons also may have contributed to the diel differences in abundances.

Lepidophanes gaussi, known as Günther's lanternfish, is a species of lanternfish distributed in the Atlantic Ocean between about 45°N and 50°S.

Feeding is acyclic in northwest Africa

Atlantic Ocean: between about 45°N and 50°S, but apparently absent from Benguela Upwelling Region and seasonally absent from off northeast Brazil.

high-oceanic; found between 425-750 m during the day and between 40-125 m at night (maximum abundance in the upper 50 m)

nektonic

Known from seamounts and knolls