Dusky Lanternfish

7.5-10 tooth patches on the lower limb of the second gill arch; 12-15 AO photophores; 36-39 lateral line organs (Ref. 36121). Pectoral fins with extremely weak and flexible rays (Ref. 36121).

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 - 16; Analspines: 0; Analsoft rays: 17 - 21; Vertebrae: 36 - 39

Oceanic and mesopelagic (Ref. 4066), found between 550-850 m during the day; between 60-850 m at night with maximum abundance between 100-150 m (Ref. 4479). Size stratification with depth during the day (Ref. 4066).

Oceanic and mesopelagic (Ref. 4066), found between 550-850 m during the day; between 60-850 m at night with maximum abundance between 100-150 m (Ref. 4479). Size stratification with depth during the day (Ref. 4066).

Lampanyctus ater

This is a large myctophid attaining a length of 140 mm (Nafpaktitis et al., 1977); maximum standard length in the Ocean Acre collections is 110 mm. In the Atlantic it is a bipolar species with a questionably subtropical distribution (Backus et al., 1977). Although L. ater does not occur in the southern Sargasso Sea, it is common near Bermuda, where it is among the eleven most abundant lanternfish in winter and late spring. The Ocean Acre collections contain 414 specimens; 211 were caught during the paired seasonal cruises, 151 of these in discrete-depth samples, of which 143 were caught in noncrepuscular tows (Table 23).

DEVELOPMENTAL STAGES.—Postlarvae were 9–22 mm, juveniles 19–64 mm, subadults 55–106 mm, and adults 82–104 mm. Most juveniles smaller than 30 mm could not be sexed, and most larger ones had recognizable ovaries or testes. All adults were male. The most sexually developed female had ovaries of moderate size with a few eggs as large as 0.25 mm in diameter. There appears to be a sexual dimorphism in size, with males developing faster and females growing to a larger size. Nearly all of the juveniles smaller than 30 mm that could be sexed were males. Juvenile females averaged nearly 5 mm larger than juvenile males (42.6 vs 38.0 mm). This difference probably is due mostly to males being recognized at a smaller size than females. Subadult females were, on the average, nearly 11 mm larger than subadult and adult males (79.6 vs 68.9 mm). A further indication of sexual dimorphism in size is that 12 of the 13 specimens 100 mm and larger were females.

REPRODUCTIVE CYCLE AND ABUNDANCE.—Lampanyctus ater has a life span of at least two years and probably does not spawn until two years of age. Recruitment of fish smaller than 30 mm occurred mostly in winter but extended into late spring, indicating that spawning occurred primarily in fall.

Abundance was greatest in winter, when the catch consisted of at least three size groups: fish 12–36 mm representing the most recent recruit class and accounting for about 65 percent of the catch, fish 42–62 mm, presumably about one year old, and fish 70 mm and larger that were probably two years old. All but two individuals 12–20 mm were taken in January, an additional indication that most spawning occurred in fall.

By late spring most recruitment was past and few fish were smaller than 30 mm. Winter recruits had grown to about 30–50 mm. The two older groups were not well represented in the samples and may be 63–73 mm and 86 mm, respectively. Abundance at this season was only slightly lower than in winter (Table 82), which is puzzling in view of the lack of recruitment.

In late summer only the most recent recruit class was adequately sampled by the discrete-depth gear. Those fish had grown to about 38–58 mm. However, specimens caught by the Engel trawl fell into three size groups: 37–58 mm. 64–85 mm, and 87 mm and larger. Presumably these groups represented those in the winter collections at a more advanced age. Abundance was about 33 percent of that at the other two seasons (Table 82).

SEX RATIOS.—Males may be more numerous than females in winter and late spring. Male-to-female ratios were 1.6:1 in winter, 2.0:1 in late spring, and 0.9:1 in late summer; only the difference in late spring was significantly different from equality (Table 83). In both winter and late spring the differences were due mostly to juveniles, and could be influenced by the size dimorphism described above. There was no consistent pattern of numerical dominance by either sex for the older stages.

VERTICAL DISTRIBUTION.—Day depth range in winter was 701–850 m, possibly extending to 1550 m, with maximum abundance at 701–750 m; in late spring 751–1200 m with a maximum at 1051–1100 m (a single specimen caught at 301–350 m probably was a contaminant); and in late summer 751–1550 m with slight concentrations at 751–850 m and 1451–1500 m. Most of the suspected day depth range of L. ater was not sampled in winter (Table 84) and little can be said concerning the vertical distribution at that season.

At night in winter and late spring two distinct depth zones were occupied: a shallow one at 51–250 m at both seasons and a deeper one at 751–900 m in winter and 751–850 m in late spring (a few specimens were taken at 551–600 m in winter). The depth of maximum abundance in winter was 801–900 m, and in late spring 51–100 m. At night in late summer L. ater was absent from the upper 600 m and was taken at 651–1000 m with maximum abundance at 851–900 m (Table 84).

Stage and size stratification were evident both day and night at each season. By day in winter and late summer juveniles had a shallower upper depth limit than subadults, and in late spring subadults had a deeper lower depth limit than juveniles. In winter and late spring juveniles were most abundant at a shallower depth than subadults were. There was an increase in size with depth at each season. Size stratification was best developed in late spring, when the minimum, maximum, and mean sizes all increased with depth. In winter and late summer the mean size of fish caught at the shallowest 50–m interval occupied was noticeably smaller than at greater depths, and in late spring the mean SL of the catch at 1051–1200 m was about twice that at 751–900 m (Table 84). At all three seasons most fish 22–50 mm were caught at 701–800 m, and all fish 90 mm and larger were below 1000 m.

At night in winter and late spring only juveniles migrated into the upper 200 m. Nonmigrants included both juveniles and subadults. Migrants were 19–46 mm and nonmigrants 18–82 mm. Fish larger than 82 mm were not taken at night.

There was a slight indication that postlarvae were stratified by size. The few 9–12 mm specimens were caught at night near 100 m, and those 15–18 mm were caught below 850 m both day and night.

Diel vertical migrations occurred only in winter and late spring. Little can be learned about the chronology of vertical migrations from the sample data, other than that some migrators arrived in the upper layer between two and three hours after sunset and some remained there until two or three hours before sunset.

PATCHINESS.—Patchiness was not indicated. The only significant CD value was for 51–100 m at night in late spring. This resulted from testing three positive samples from 100 m, showing little variation, with negative samples from 54–56 m and 92–94 m. This probably indicates a stratified abundance within this depth rather than horizontal patchiness.

NIGHT:DAY CATCH RATIOS.—Night-to-day catch ratios, including interpolated values, were 0.6:1 in winter and late spring, and 1.0:1 in late summer (Table 85). Most of the difference between day and night catches in winter was due to juveniles, and most of the difference in late spring to subadults. In winter juveniles were concentrated below 700 m both day and night, but also were found at 51–250 m at night. The greater night vertical range may account for part of the difference between winter day and night catches. In late spring most of the difference in day and night catches was due to subadults.

Nannobrachium atrum (Tåning, 1928)

Lampanyctus ater Tåning, 1928:68 [original description, North Atlantic]; 1932, pl. 128 [description, figure].—Parr, 1928:88, 104–106 [key, western Atlantic, figured, description].—Nybelin, 1948:40 [eastern Atlantic].—Bolin, 1959:33 [discussion, distribution].—Bullis and Thompson, 1965:28 [northern Gulf of Mexico].—Bekker, 1967a: 116 [equatorial Atlantic and Sargasso Sea].—Nafpaktitis and Nafpaktitis, 1969:44–45, fig. 53 [description, South Indian, lectotype figured, listed as holotype].—Quero, 1969:4 [northeastern Atlantic].—Badcock, 1970:1026 [discussion, depth distribution, Canary Islands].—Gibbs and Roper, 1971:129 [diurnal vertical migration].—Gibbs et al., 1971:43, 105–106 [key, vertical distribution near Bermuda, figure].—Hulley, 1972:225 [description]; 1981:188–190 [description, Atlantic distribution]; 1984a:62, 79–82, figs. 12, 13 [in part] [description]; 1984b:461 [description, northeast Atlantic distribution]; 1986b:243 [zoogeography]; 1986c:307, fig. 86.75 [description, South Africa, figure]; 1990:163, 164 [figured, Southern Ocean].—Krefft and Bekker, 1973:187 [biology, synonymy].—Nafpaktitis, 1973:38–40 [redescription, designation of lectotype, figure].—Nielsen, 1974:38 [listing of lectotype].—Parin et al., 1974:106 [southwest Atlantic].—Bekker et al., 1975:314 [distribution, Caribbean Sea].—Badcock and Merrett, 1976:42 [30°N, 23°W].—Brooks, 1976:569, 575, 581 [swimbladder size].—Parin and Golovan, 1976:263 [off West Africa].—Wisner, 1976:175 [figure, discussion].—Nafpaktitis et al., 1977: 203–206, fig. 139 [description, distribution, figure].—Backus et al., 1977:267, 275, 277 [zoogeography].—Parin et al., 1978:175 [?in part?] [eastern tropical Atlantic].—Paxton, 1979:14 [lectotype].—Gushchin and Kukuev, 1981:37 [in part?] [53°N, 30°W].—Brandt, 1983:235, 240 [?in part?] [in warm core eddy east of Australia].—Moser et al., 1984:239 [relationships, larval description].—Hulley and Krefft, 1985:35, 40–46 [North Atlantic zoogeography].—Rubies, 1985:578, 584 [Valdivia Bank off Namibia, gill raker numbers].—Gartner et al., 1987:86, 88, 91, 95 [eastern Gulf of Mexico].—Kailola, 1987:103 [?in part] [Solomon Sea].—Kamella, 1987:52, 102–105, 149–159, 164 [ecology and biology near Bermuda].—Scott and Scott, 1988:221 [description, Nova Scotian shelf].—Paxton and Hanley, 1989:264 [Australian distribution].

Lampanyctus niger.—Norman, 1930:331 [in part] [Discovery Expeditions].—[Not Günther, 1887.]

Macrostoma atrum.—Fowler, 1939:1231 [repeats original description].

Lampanyctus (Lampanyctus) ater.—Fraser-Brunner, 1949:1086 [illustrated key].—Bekker, 1983:87, 88, 199, 200 [key, description, distribution].

?Lampanyctus niger.—Smith, 1949:123 [description, South Africa, figure] [determination fide Hulley, 1986c:307].—[Not Günther, 1887.]

Paralampanyctus ater.—Kotthaus, 1972b:29 [western tropical Indian].—Kotthaus, 1972a: 14 [in part?] [eastern North Atlantic].

Lampanyctus niger-ater complex.—McGinnis, 1982:41–43, 66 [distribution south of 30°S, relationships, zoogeography].

COMPARATIVE DIAGNOSIS.—Nannobrachium atrum (Figure 6) can be distinguished from the other species of the Nigrum group and from N. crypticum in the Achirus group primarily by its gill raker count (total 16–18) and number of lower limb tooth patches on the second gill arch (7.5–10) (both higher than in N. gibbsi, N. indicum, and N. crypticum) and by the number of its AO photophores (12–15), lateral line organs (36–39), and vertebrae (36–39) (all higher than in N. nigrum, N. indicum, and N. crypticum) (Table A1). In addition, the SAO series is farther forward in N. atrum than it is in N. nigrum. It can be distinguished from all other species of Nannobrachium by the combination of characters in Table 1.

DESCRIPTION.—Counts are based on up to 56 specimens from the North and South Atlantic, Indian, and South Pacific oceans and are given in Tables A1–A8.

Proportions: Given in Table 4.

Fins: Origin of anal fin behind vertical from middle of base of dorsal fin. Pectoral fin barely reaching vertical from PO3, its rays weak, flexible. Base of adipose fin above end of anal-fin base, its origin well before end of anal-fin base.

Luminous Organs: PLO 1–3 times its diameter below lateral line. PO4 slightly higher than level of PVO2 and above PO3 or slightly anterior to vertical from PO3. VLO less than one photophore diameter below, frequently nearly touching, lateral line. SAO2 always behind vertical from VO4 but usually closer to VO4 than to AOa1. SAO3 before vertical from AOa1. AOa1 slightly depressed and AOa1–2 interspace enlarged. AOp1 at or behind end of anal-fin base. Prc well separated from AOp; Prc1–2 on horizontal line; Prc3–4 on or nearly on vertical line, well behind Prc2. Supracaudal and infracaudal luminous scales well developed, often with single separated scale preceding infracaudal gland. No secondary photophores found.

Size: The largest specimen examined was 133 mm from off New Zealand, whereas the largest specimen examined from the Atlantic was 119 mm, taken by the Walther Herwig in the North Atlantic. Nafpaktitis et al. (1977) suggested that this species may attain a maximum size of 140 mm. Hulley (pers. comm., 1980) reports a size of 129 mm and suggests sexual maturity at about 90–100 mm. The largest specimen that he examined from South Atlantic Walther Herwig material was 120.2 mm (Hulley, 1981).

Material: 741 (20–133 mm) specimens were examined, including the lectotype, 89 mm, ZMUC P2330209, Dana sta 1152 1, 30° 17′N, 20°44′W, 22 October 1921.

VARIATION.—Nannobrachium atrum, the most widely distributed species of Nannobrachium, is found in the South Pacific and Indian oceans and in the Atlantic Ocean, where it is bipolar and absent from the central area (Figure 5). Nafpaktitis et al. (1977) reported N. atrum to have a daytime maximum abundance in the North Atlantic at 700–800 m and to be as shallow as 100 m at night. Karnella (1987) reported greater depth ranges for Ocean Acre material, with a late spring maximum at 1051–1100 m.

Despite the broad distribution, no differences were found in absolute numbers or frequencies of gill rakers on the first arch, lower limb tooth patches of the second arch, or body shape that would show up as proportional differences. Only slight differences were found in the frequencies of AOp and total AO photophore counts, dorsal- and anal-fin ray counts, and numbers of infracaudal luminous gland scales (Table 5). Southwest Pacific specimens tended to have the VLO rather far posteriad, which was the only photophore positional difference. No differences were noted in specimens from the eastern and western North Atlantic and the Gulf of Mexico.

Two specimens, one from the Indian Ocean and one from the Pacific, with exceptionally high numbers of anal-fin rays (21), deserve special comment. The Indian Ocean specimen (LACM 31332-4, 69 mm) was collected by the Anton Bruun and, thus, was part of the material described by Nafpaktitis and Nafpaktitis (1969:44). In addition to the high number of anal-fin rays, it is atypical both in the lower-limb tooth patch count on the second gill arch (10 on both sides versus the common number of 9 or rarely 10 on one side in typical N. atrum) and in its count of 8 AOa plus 6 AOp (both sides). A further mystery is the origin of this specimen. The bottle label lists only one specimen (86 mm) instead of the two it actually contains. Nafpaktitis and Nafpaktitis (1969:44) listed the material of N. atrum that they examined from the Indian Ocean and included the 86 mm specimen as the only one from that collection (label number 7133). They recorded neither the 69 mm specimen nor the atypical AO count of 8+6 in their table 9, so it appears that they did not see it.

The Pacific Ocean specimen with 21 anal-fin rays (ZMUC, Dana 3631 III, 96.5 mm) is from 35°40′S, 176°40′E, which is north of New Zealand. Besides the anal-ray count, it has two abnormalities: a gill raker count of 5 + 11 on the right side (the left side is the typical N. atrum count of 5 + 12) and the SAO2 slightly far back in position so that it is closer to the AOa1 than to the VO4 (as is typical in N. nigrum). Determination of the status of these specimens requires study of more material.

One other atypical and damaged specimen is in the collections of the South African Museum (SAM 23712), and it came from the South Atlantic. It appears to be a typical specimen of N. atrum, except that the intact left VLO is far below the lateral line (about 4 photophore diameters). The pectoral-fin base is narrow, but the fins are badly broken, so it is impossible to estimate their original length, but the rays appear to be stiff enough that they resemble some specimens of the Regale group. In all other characters, considering the damaged condition, it is a fairly typical specimen of N. atrum, except for a gill raker count on the right side of 5 + 13 (but with a more typical 5+12 on the left side). Again, determination of status awaits further study.

Western Atlantic: Grand Bank and from Brazil to Argentina

oceanic and mesopelagic, found between 550-850 m during the day; between 60-850 m at night with maximum abundance between 100-150 m

nektonic