Myctophum nitidulum Garman 1899

Branchiostegal rays: 9-10 (Ref. 31442). Anal organs 14; male supracaudal gland has 5-8, female infracaudal gland with 2-6 small, round to oblong spots, respectively; may be distinguished from all other Myctophum possessing cycloid scales by its angulate, non-serrate, posterodorsal margin of the operculum (Ref. 39633).

Oviparous (Ref. 31442).

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: 18 - 21; Vertebrae: 36 - 39

High-oceanic, nyctoepipelagic at the surface and to 950 m and generally found between 475-850 m during the day (Ref. 4479). Neustonic to mesopelagic (Ref. 58302). Oviparous, with planktonic eggs and larvae (Ref. 31442). Lipid content is 3.8 % in fresh body weight and wax ester is 10.6 % in total lipids (Ref. 9193). Females reach sexual maturity at 4.8 cm, males at 3.5 cm (Ref. 47377).

Myctophum nitidulum

This large myctophid grows to about 100 mm (Nafpaktitis et al., 1977); the largest specimen caught during the program was 80 mm. Myctophum nitidulum, a tropical-subtropical species (Backus et al., 1977) is common but not abundant in the study area, never being among the 10 most abundant lanternfishes (Table 131). It is represented in the Ocean Acre collections by 543 specimens; 229 were taken during the paired seasonal cruises, 180 of these in discrete-depth samples of which 163 were caught in noncrepuscular tows (Table 23). Myctophum nitidulum was not well sampled by the IKMT; approximately 95 percent of all specimens were caught at night in neuston nets.

DEVELOPMENTAL STAGES.—Postlarvae were 9–16 mm, juveniles 14–42 mm, subadults 44–69 mm, and adults 55–80 mm. Fish less than 27 mm could not be sexed; most of those 27–31 mm and all larger ones were sexed. Males larger than about 35 mm have luminous tissue dorsally on the caudal peduncle, and females larger than about 45 mm have luminous tissue ventrally on the caudal peduncle (Gibbs, 1957). There is no apparent sexual dimorphism in size among the relatively few large specimens (over 40 mm) in the Ocean Acre collections. Males and females were about equally represented among the 67 specimens examined for sex (34 vs 33, respectively).

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—Spawning occurs from spring to fall, with a peak in intensity in late spring–early summer. The life span may be two or three years, but too few large specimens were caught to be sure. Abundance was greatest in late summer, when most specimens were smaller than 20 mm, and progressively decreased in winter and late spring (Table 120).

Although juveniles predominated in each season, those 14–16 mm were taken only in late spring and late summer. Those smaller than 20 mm were most abundant in late summer. The seasonal distributions of postlarvae (June-October, most in late summer) and adult females (April-September), combined with that of small juveniles, shows that most reproduction takes place in spring and summer.

By late spring spawning had begun, and the catch consisted of recently spawned postlarvae 8–14 mm and juveniles 14–19 mm, fish 28–44 mm presumed to be about one year old, and fish larger than 54 mm about two or more years old. Abundance was dominated by specimens 17–18 mm, which accounted for about 65 percent of the nighttime catch. Adults, although not taken in abundance at any season, were most abundant in late spring.

In late summer recruits 15–19 mm were predominant, accounting for more than 95 percent of the abundance at that season. All specimens caught in discrete-depth samples were 15–28 mm. However, several specimens larger than 60 mm were caught with the Engel trawl at that season, showing that at least two year classes were present. Abundance was greatest at this season (Table 120) as a result of the spawning peak in late spring–early summer.

About 90 percent of the catch in winter was due to juveniles 21–30 mm. Presumably these specimens represented late summer recruits but at an older age. Larger fish were either 34–47 mm or 60–77 mm. These larger specimens probably belonged to different year classes, but their abundance was too low to be certain. The 60–77 mm specimens were at least a year older than the 21–30 mm fish. The age of the 34–47 mm group was uncertain; they may have represented the earliest fish spawned the previous spring.

Additional evidence for a late spring–early summer spawning peak is seen in the catch in September when more than 200 individuals, mostly less than 30 mm, were taken in neuston samples.

VERTICAL DISTRIBUTION.—Little is known about the daytime depth range of M. nitidulum. The five specimens caught in discrete-depth trawls were from 601–950 m, with only postlarvae taken below 850 m (Table 120). Clarke (1973) reported a similar diurnal depth range for M. nitidulum near Hawaii. Gibbs et al. (1971) reported that two 11-mm juveniles were caught at 301–350 m, during the day. This is in error; the fish in question were M. selenops and not M. nitidulum. Fully transformed juveniles of M. nitidulum are not likely to be as small as 11 mm, as transformation occurs at about 14 mm (Moser and Ahlstrom, 1970; H.S. Zadoretzky, personal communication), the size of the smallest juveniles in the Ocean Acre collections.

At night most specimens were caught in neuston nets, and a few were taken at scattered depths down to 950 m (Table 120).

PATCHINESS.—A patchy or clumped distribution was noted at the surface by night in each season. Table 121 gives the number of specimens per hour taken in neuston samples between sunset and sunrise and, despite averaging samples made within one-hour intervals, shows a clumped distribution.

NIGHT:DAY CATCH RATIOS.—Night-to-day catch ratios are 18.0:1 in winter, 20.7:1 in late spring, and 16.4:1 in late summer. The small day catches may have been related to vertical distribution rather than enhanced net avoidance, because most of the night catch (made in neuston nets) in each season consists of fish smaller than 30 mm (Table 120). Presumably fish of this size cannot avoid the IKMT. However, the daytime distribution of this and other species taken in large numbers at night in neuston nets remains a mystery.

分布於世界三大洋溫暖海域。臺灣則發現於東沙群島周邊水域。

一般以底拖網捕獲，不具食用經濟價值，通常做為下雜魚用。

體延長，側扁，後部略細。頭中等大。吻短，前端鈍。眼大。口大，上頜骨狹長而延伸至前鰓蓋後緣，末端略擴大；上下頜呈絨毛狀齒帶。鰓蓋後上緣呈角狀，無鋸齒狀突起。體被大而薄圓鱗，易脫落；側線平直。背鰭單一，位於體中部，具軟條13-15(通常為14)，後部另具一脂鰭；臀鰭基底略等於背鰭基底，具軟條22-26(通常為24)；尾鰭叉形，尾鰭副鰭條柔軟。各部位之發光器位置於下：鼻部背位發光器(Dn)及鼻部腹位發光器(Vn)皆小而圓形；鰓蓋位發光器(Op)2個，位於前鰓蓋後緣下方，Op1較Op2小，均在眼眶下緣縱線之下；鰓被架位發光器(Br)3個；胸鰭上方發光器(PLO)，距側線比距胸鰭基部遠；胸鰭下方發光器(PVO)2個，兩者互為斜線排列；胸部發光器(PO)5個，PO5位置略昇高；腹部發光器(VO)4個，水平排列；腹鰭上位發光器(VLO)位於腹鰭和側線之中間；臀鰭上方發光器(SAO)3個，三者排列呈斜線，SAO1在VO4的上方或稍後上方，SAO3緊臨在側線下緣約1/2直徑處；體後側位發光器(Pol)1個，在脂鰭下方，緊臨側線下緣；臀鰭前部發光器(AOa)9-10個，水平排列；臀鰭後部發光器(AOp)5-6個；尾鰭前位發光器(Prc)2個。尾部發光腺，雄魚的SUGL具5-8個，雌魚的INGL具2-6個發光鱗。

大洋性中層巡游魚類，具日夜垂直分布習性，白天一般棲息深度可達475-850公尺左右，晚上則上游至水深0-30公尺附近處覓食，以浮游生物為食。

Myctophum nitidulum, common name pearly lanternfish, is a species of deep sea fish in the family Myctophidae, the "lanternfish".

Western Atlantic: between about 42°N and 31°S

High-oceanic, nyctoepipelagic at the surface and to 950 m and generally found between 475-850 m during the day.

nektonic

Known from seamounts and knolls