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): 12 - 14; Analspines: 0; Analsoft rays: 12 - 14

Oceanic (Ref. 4066), found between 300-600 m during the day and between 50-300 m at night, exhibiting size stratification with depth (Ref. 4479).

Mesopelagic (Ref. 58302). Oceanic (Ref. 4066), found between 300-600 m during the day and between 50-300 m at night, exhibiting size stratification with depth (Ref. 4479). Reach sexual maturity at a length of 3 cm (Ref. 47377).

Diaphus mollis

This moderate-sized lanternfish is known to attain 66 mm (Hulley, 1981); it grows to 50 mm in the study area. A tropical-subtropical species, D. mollis is a ranking myctophid in the North Atlantic subtropical region (Backus et al., 1977). It is a “common” lanternfish in the study area ranking 11th to 14th in abundance at all seasons (Table 131). It is represented in the Ocean Acre collections by 1559 specimens; 650 were caught during the paired seasonal cruises 461 of these in discrete-depth samples, of which 342 were caught in noncrepuscular tows (Table 23).

DEVELOPMENTAL STAGES.—Postlarvae were 5–11 mm, juveniles 9–26 mm, subadults 25–49 mm, and adults 30–48 mm. Most juveniles less than 17 mm had thread-like gonads and could not be sexed. Adult females had eggs as large as 0.5 mm in diameter. Subadult males had a greatly enlarged luminous patch beneath the eye (Nafpaktitis, 1968), and tended to be larger than subadult and adult females (mean SL 38.4 mm vs 35.8 mm). Size ranges of both sexes were similar: males 13–48 mm and females 14–49 mm.

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—Diaphus mollis has a one-year life cycle, with only a few individuals surviving much beyond a year. Spawning occurs from early spring to fall, perhaps with a peak in intensity in late spring. Abundance is greatest in late summer, when D. mollis was the eleventh most abundant lanternfish. Juveniles were most abundant in late summer, subadults in winter, and adults in late spring (Table 48).

Adult-size females were taken throughout the year, but enlarged ovaries with eggs larger than 0.1 mm in diameter were observed only from April through November. Small juveniles (less than 20 mm) and postlarvae were most numerous in late summer. These seasonal distributions indicate that spawning occurs from spring to fall with a peak in intensity in late spring to early summer. At each season, subadult females within the adult size range (larger than 39 mm) were taken, suggesting that some individuals may live longer than one year and may spawn more than once. Unlike that near Bermuda, some populations of D. mollis apparently breed in winter (Nafpaktitis, 1968).

In late spring more than 80 percent of the population consisted of subadults and adults, with subadults half-again as abundant as adults (Table 48). Seasonal abundance of adults and their proportion of the population were greatest at that time. Juveniles were mostly larger than 20 mm and probably were from the previous year's spawn. Recruits from the spawn underway at that time apparently were too small to be adequately sampled by the nets, as only one postlarva was taken. Subadult and adult females were equally abundant (Table 49), but less than half of the subadults were as large as the smallest adult. This suggests that by late spring less than 25 percent of the female population had spawned and that the peak in spawning had just been reached or was yet to be reached.

In late summer recruits 9–25 mm accounted for more than 80 percent of the catch, subadults for about 12 percent, and adults about 8 percent (Table 48). Abundance of postlarvae almost certainly was underestimated at this season; about 80 percent of the total number were caught in late summer, but very few were included in samples used to estimate abundance. Juveniles 11–16 mm were most abundant and probably represented offspring of the spawning peak.

Juveniles accounted for about 16 percent of the population sampled in winter, subadults more than 82 percent, and adults 1.5 percent (Table 48). The reduced abundance of juveniles from late summer to winter, and the fact that all juveniles less than 19 mm were taken in January and all larger ones were taken in February to March, indicates that little or no recruitment into the population occurred after fall. Continued growth of the spring and early summer spawn resulted in the observed dominance of subadults in winter. A few subadults were greater than 40 mm and may have been in their second year of life. The lack of adult females further indicates a winter hiatus in spawning activity.

SEX RATIOS.—Males were more numerous than females at each of the three seasons (Table 49), with male-to-female ratios of 1.1:1 in winter, 1.9:1 in late spring, and 1.2:1 in late summer. Only the late spring ratio differs significantly from equality (Table 49). The difference in late spring was due mostly to subadults, for which the male-to-female ratio was 2.5:1, but adults also contributed to the difference. Except for subadults in late spring, none of the individual stage sex ratios was significantly different from equality (Table 49). The difference in late spring may be related to postspawning mortality, which presumably is greater for females.

VERTICAL DISTRIBUTION.—Diurnal depth range in winter was 451–500 m; in late spring the upper 50 m and 301–700 m with no concentration at any particular depth; and in late summer 101–150 m and 301–850 m with maximum abundance at 551–600 m. At night most specimens were taken in the upper 250 m with maxima at 51–100 m in winter and late spring, and 33–100 m in late summer (Table 50).

The shallow captures made by day in late spring (301–350 m) and late summer (101–150 m and 301–350 m) may represent valid records. It is unlikely that the specimens were contaminants, because several samples immediately preceding each positive shallow sample contained few or no specimens. However, if these depths are part of its diurnal vertical range, the species has a most unusual dispersal within the water column, with alternating positive and negative depth intervals.

Stage and size stratification were evident only at night. The lack of stratification by day may be an artifact of sampling, especially in winter and late spring, when the day catches were small (Table 50). In late summer almost 90 percent of the diurnal catch was juveniles, with most of the remainder subadults. Juveniles were captured both shallower and deeper than subadults, but both developmental stages had similar depths of maximum abundance. At 601–650 m all specimens captured were 9 mm (Table 50), which is thought to be the size at transformation (Nafpaktitis, 1968).

At night juveniles were most abundant in the upper 50 m at all seasons, subadults at 51–100 m at all seasons, and adults at 51–100 m in late spring and 151–200 m in late summer and winter. Subadults and adults occurred at greater depths than juveniles in winter and late spring, but juveniles were taken both shallower and deeper than subadults and adults in late summer. A 7 mm postlarva was taken in the upper 50 m during the day in late spring, suggesting that smaller postlarvae may inhabit the upper 50 m.

As would be expected from the observed stage stratification, size stratification also was quite prominent at night. Only the smallest individuals migrated into the upper 50 m at night in each season; all but two specimens (one, 27 mm, in winter and one, 21 mm, in late spring) captured at that depth were smaller than 20 mm SL (Table 50). Except for three juveniles taken between 201 m and 700 m in late summer, all individuals less than 35 mm SL were taken in the upper 100 m, and all those greater than 34 mm SL were below 100 m in each season. The mean size of specimens captured in the upper 100 m was noticably smaller than that of those taken below 100 m (Table 50).

Regular diel vertical migrations occurred at all seasons; only a single individual (a 17 mm juvenile in late summer) was taken at day depths during the night.

Migration times could be determined only for late summer due to the poor day catches in winter and late spring. An upward migration time of about 5.0 hours and a downward migration time of about 3.5 hours are suggested by capture data for D. mollis. Day depths were still occupied between 3.0 and 4.0 hours before sunset, and the species was taken in the upper 50 m by 1.5 hours after sunset. Day depths were occupied between 2.5 and 3.5 hours after sunrise, and some depths within the nocturnal range were still occupied at or near sunrise; specimens were captured at about 90 m and 200 m, but not at 45 m or 110 m. Assuming an upward migration time of 5.0 hours and a downward migration time of 3.5 hours, migration rates of 92 m/hr and 131 m/hr, respectively, were obtained for diel migrations between depths of maximum abundance.

PATCHINESS.—Apparently the species is well dispersed by day at all seasons. The only significant CD value (for samples from 101–150 m in late summer) was the result of a single positive collection taken near the beginning of the evening crepuscular period; specimens captured in that sample may have been early migrants. At night, clumped distributions were indicated at 50–100 m in winter, and 51–100 m in late spring and late summer. At each season the two most abundant developmental stages apparently were responsible for all or most of the clumping (Table 50). Significant clumping was indicated at the depth of maximum abundance of juveniles (50 m) and subadults (51–100 m) in winter, and subadults and adults in late spring. In late summer significant clumping was not indicated at the depth of maximum abundance (33 m) of juveniles, but only two samples were made in the upper 50 m. Clumping was indicated in late summer at 51–100 m where juveniles also dominated the catch. Subadults were most abundant at that depth.

NIGHT:DAY CATCH RATIOS.—Night-to-day catch ratios for discrete-depth samples were 3.3:1 in winter, 2.2:1 in late spring, and 1.4:1 in late summer (Table 51). Catch rates for each of the three older stages were greater at night than by day for each season sampled, but subadults and adults were relatively much more abundant at night than juveniles. In late summer, when juveniles accounted for almost 85 percent of the combined day and night catches, the night-to-day catch ratio was least deviant from 1 to 1. As would be expected from these observations, the mean size of specimens taken at night was greater than that of specimens taken by day at each season (35.6 vs 34.5 mm in winter, 38.2 vs 37.2 mm in late spring, and 18.2 vs 15.6 mm in late summer). In winter and late summer, specimens larger than 40 mm were taken only at night. The fact that the ratios appear related to size suggests that increased net avoidance by day was mainly responsible for low day catches.

體側扁，尾柄略長。吻短而鈍，兩眼間稍平。口裂大，上頜骨後部不擴大，末端伸達眼眶緣後下方；眼大，眼徑大於吻長的2倍，瞳孔水平方向伸長，水晶體前方出現空隙。　鰓蓋後緣鈍尖，鰓孔大，鰓膜分離不與峽部相連。鰓耙短而寬，葉狀。體被圓鱗，易脫落。側線完全。背鰭1個，起於腹鰭起點上方。臀鰭起於背鰭末端的後下方，背、臀鰭基長幾相等。脂鰭於臀鰭末端上方。胸鰭位低，鰭條不達腹鰭基，腹鰭基離胸鰭基較臀鰭基近，鰭條達臀鰭基。尾鰭分叉。甲醛液浸標本體顯褐色。發光器：鼻部背位發光器(Dn)較大，圓形，位於嗅囊背後方的黑色杯形凹陷中；鼻部腹位發光器(Vn)呈長條形， 從眼眶前緣下方沿腹緣向後延伸，達水晶體前緣稍後下方，眶下位發光器(SO) 小而圓，So和Vn的間距較短，約為Vn長度的'1/2；鰓蓋位發光器(Op)2個，Op1較小，於口角後方；鰓被架位發光器 (Br)3個；胸鰭上方發光器(PLO)離胸鰭基較側線稍近，其下方發光鱗小，稍大於PLO；胸鰭下方發光器(PVO)2個，成斜線排列；胸部發光器(PO)5個，PO4位置升高；腹鰭上位發光器(VLO)於側線和腹鰭基的中間；腹部發光器(VO)5個，VO2和 VO3位置逐漸升高成斜直線；臀鰭上方發光器(SAO)3個，成鈍角排列，SAO1於 VO5的後上方，SAO2靠近SAO1，SAO3於側線下方2倍SAO直徑處，且在VO5， SAO1和SAO2連線的延長線前方；臀鰭前部發光器(AOa )5個，成弧線排列，AOa1位置升高，但低於SAO2，最後1個AOa 位置亦升高；體後側位發光器(Pol)1個，離側線距離和SAO3同；臀鰭後部發光器(AOp)5個，均在臀鰭末端之後上方；尾鰭前位發光器(Prc)4個，前面3個Prc幾呈一條水平線，Prc4位置升高至側線下方1.5倍Prc直徑處。

Diaphus mollis, the soft lanternfish, is a species of lanternfish found in the Atlantic and Indian Oceans.

Canada to Argentina

Occasionally found in Canadian Atlantic waters. Found at depths of 50- 600 m.

nektonic

Known from seamounts and knolls