Diaphanous Hatchet Fish

View data on Catalog of Fishes here.

Dorsal-fin rays 9–11; anal-fin rays 14–16; pectoral-fin rays10–11; total gill rakers 7–8 (rarely 9); vertebrae 29 (rarely 30). Medium size species, seldom exceeds 55 mm SL; trunk very broad; its depth usually greater than its length; dorsal spine long, its length greater or equal to dorsal fin length; posterior anal pterygiophores short, little extension behind and on same level with anal photophores; supra-anal photophore low, not reaching more than one-half the distance from ventral body margin to midline, no body margin extension in front of anal photophores; jaws medium to small; teeth short and low; gill raker tooth plates with low spinate ridges; anterior dorsal surface of tongue with small nodules; postabdominal and anal pterygiophore spines usually shorter than others in genus; in preservative pigment dark dorsally, often light and dispersed in trunk region, usually little pigment present at base of caudal rays.

Differs from S. pseudobscura by its smaller mouth, shorter teeth and no gill-raker tooth plate spines; markedly lower supra-anal photophore; relatively short anal pterygiophores not extending to level with anal photophores. Differs from S. obscura short dorsal spine and relatively short body depth.

Broadly distributed in the Atlantic, caught in moderate numbers in the South Atlantic off Brazil and from 20˚N to the African coast at about 35˚S; abundantly present in the Gulf of Guinea and the tropical Atlantic; taken abundantly in the southern Caribbean, the Gulf of Mexico, and Straits of Florida; taken in the western North Atlantic; a large population occurs in the north eastern Atlantic from 25°N to 45°N latitude. In the western Indian Ocean small to moderate catches extend from 5 °S to 35°S latitude, a single catch has been observed from the eastern Indian Ocean; numerous catches indicate this species present south of Java, near Borneo, and in the Banda Sea; known also between New Guinea and the Solomon Islands, it occurs in the western Pacific near the Philippines and along the coast of Japan, with a small sample taken in the North Pacific; this species occurs in small numbers off lower California; has been reported abundantly southeast of Hawaii; a large population extends across the South Pacific from Chile to about 160° W longitude.

Distributed between 400 m and 1200 m; major concentrations occur between 700 m and 900 m; no diurnal movement or marked geographical depth variation could be detected by Baird (1971).

Baird RC. 1971. The Systematics, Distribution, and Zoogeography of the Marine Hatchetfishes (family Sternoptychidae). Bulletin of the Museum of Comparative Zooology 142(1):1–128.

Baird RC. 1971. The Systematics, Distribution, and Zoogeography of the Marine Hatchetfishes (family Sternoptychidae). Bulletin of the Museum of Comparative Zooology 142(1):1–128.

To about 55 mm SL.

Off Panama [Caribbean Sea, Western Atlantic, 11°6'N, 78°21'W] [original locality Jamaica].

Neotype: MCZ 46402.

Oceanic and non-vertical migrant (Ref. 4739). Commonly found in 500-800 m both day and night (Ref. 4054). Possibly a cyclic feeder of copepods, ostracods, euphausiids, amphipods, fishes and other taxa (Ref. 4739). Feed on fewer but larger prey items from regions of cooler overlying water massess and diet was less diverse than that of fish from warmer waters (Ref. 54153). Larger specimens feed on larger food items. Feeding strategy appears to involve capture of the nearest "available" prey within its immediate vicinity (Ref. 54153).Adult photophore complement acquired at 11-13 mm SL (Ref. 4739). Lipid content 1.4 % in fresh body weight and wax ester is 4.2 % in total lipids (Ref. 9193).

Dorsal spines (total): 0; Dorsal soft rays (total): 9 - 11; Analspines: 0; Analsoft rays: 12 - 16

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.

Triangular transparent membrane present above anal fin base (Ref. 13608).

Oceanic and non-vertical migrant (Ref. 4739). Mesopelagic at 275-1200 m (Ref. 58302). Commonly found in 500-800 m both day and night (Ref. 4054). Possibly a cyclic feeder of copepods, ostracods, euphausiids, amphipods, fishes and other taxa (Ref. 4739). Adult photophore complement acquired at 11-13 mm SL (Ref. 4739). Lipid content 1.4 % in fresh body weight and wax ester is 4.2 % in total lipids (Ref. 9193).

fisheries: of no interest

Sternoptyx diaphana

Sternoptyx diaphana is broadly distributed in the Atlantic, Pacific, and Indian oceans. In terms of the Atlantic faunal regions proposed by Backus et al. (1977), the species is most abundant in the Gulf of Mexico, the North Atlantic subtropical, and the Atlantic tropical regions, but scattered catches have also been made in the North Atlantic temperate, the Mauritanian Upwelling, and the South Atlantic subtropical regions (Baird, 1971).

This is a medium-size sternoptychid, ranging from 5–36 mm SL in the Ocean Acre area, although specimens as large as 46 mm have been reported from the Gulf of Mexico (Schultz, 1961), and as large as 54 mm from the Pacific (Haig, 1955). S. diaphana was the most abundant sternopitychid in the Ocean Acre area in winter and late spring and second in abundance in late summer (Table 5). A total of 2728 specimens was captured in the 14 cruises; 1237 were taken during the seasonally paired cruises, including 613 in discrete-depth samples, with 541 of these from noncrepuscular tows (Table 4).

DEVELOPMENTAL STAGES.—Sex and/or developmental stage were determined for 2702 specimens of S. diaphana. Postlarvae were 5–9 mm (mean = 6.4 mm), and juveniles 7–15 mm (mean = 9.6 mm). It was not possible to determine sex in these two stages. Subadult females were 10–32 mm (mean = 16.6 mm); adults 20–36 mm (mean = 26.5 mm). Males were difficult to stage due to the gradual and subtle changes in the testes with maturation. On the basis of microscopic examination and sizes of subadult and adult females, an arbitrary demarcation between subadult and adult males was drawn between 18 and 19 mm SL. On this basis, subadult males ranged from 11–18 mm (mean = 16.0 mm), and adults from 19–32 mm (mean = 23.8 mm). The largest females were 1–3 mm longer than the largest males. However, when length-frequencies of subadults and adults from all cruises are combined for each sex, the mean size is the same for both sexes (21.4 mm), and the median size of males (22.0 mm) is greater than that of females (20.0 mm). Probably there is little or no sexual dimorphism in size.

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—Sternoptyx diaphana breeds throughout the year, with an extended peak in spawning from June through November or December. Both sexes appear to have a one-year life cycle, and most die after spawning. The June to December spawning peak is indicated by the increase in both absolute and relative abundance of adults from winter to late summer and by the relative abundance of postlarvae in late summer and winter (Table 6). The presence of some postlarvae and gravid adults in late spring confirms that some spawning also occurs at this time.

A one-year life cycle is suggested by the seasonal abundance of the various life history stages. The combined abundance of postlarvae, juveniles, subadults, and adults was highest in winter, intermediate in late summer, and lowest in late spring (Table 6). In late summer the catch per unit effort of ripe adults was at its highest level, and postlarvae were also relatively abundant. Both are indications of heavy spawning activity. Juveniles also were relatively abundant. These were only slightly longer (about 3 mm) than the postlarvae and represent growth of postlarvae that were spawned during the summer months. The percentage of subadults was at its lowest level in late summer, suggesting a maturation of most subadults into the adult stage.

By winter, the catch per unit effort of postlarvae had increased slightly, indicating that spawning had continued throughout the fall. Juveniles were very abundant, accounting for over half the catch. Since metamorphosis in the genus Sternoptyx is protracted (Ahlstrom, 1974), these probably represent continued growth of postlarvae that were produced in the late summer and early fall months. Subadults were also at their peak yearly abundance. They were about 7 mm longer than the juveniles and probably represent continued growth of juveniles that were present during late summer and early fall. Adults, on the other hand, were relatively scarce from November through February (cruises 1, 5, 11, 13), and their decline from late summer is an indication of postspawning mortality. Two females (26 and 32 mm) taken in winter were staged as subadults on the basis of ovary appearance. These were well into the size range associated with adults and may have spawned previously and survived to approach a second spawning.

In late spring, total abundance was at its lowest level. Postlarvae were at their lowest yearly abundance. This was due to several factors, including a decrease in spawning activity, continued loss through natural mortality, and growth of these individuals into the juvenile stage. Relative to winter catches, the percentage of juveniles had decreased, while the percentage of subadults had increased. This trend is also apparent in data from March (cruise 2) and April/ May (cruise 6). This indicates that individuals were moving from the juvenile to the subadult stage through continued growth. The percentage of adults increased from winter to late spring, presumably due to the maturation of winter subadults.

The one-year life span of this species can be illustrated and summarized by following the development of a particular cohort. For example, postlarvae produced in late summer would develop into juveniles by the late fall or winter, and these in turn would grow into subadults by the winter or early spring. Development would then continue through the spring and summer months until maturity was reached the following late summer or early fall. At this time they would spawn and subsequently die. Different cohorts of fish would follow a similar developmental schedule except that their year of life would begin and end in different seasons.

SEX RATIOS.—No significant difference between total numbers of males and females was indicated in any of the three seasons (Table 7). In actual numbers, more females than males were taken in winter (56:39) and more males than females in late spring (141:119) and late summer (88:70). Subadult females were significantly more numerous than subadult males in both winter and late summer, and adult males significantly outnumbered adult females in all seasons. Although this reversal in sex ratios may be partly due to the somewhat arbitrary delineation between subadult and adult males, the data suggest that adult males outnumber adult females.

VERTICAL DISTRIBUTION.—The major concentration of S. diaphana is from 700–1000 m. Of the 541 discrete-depth noncrepuscular specimens captured during the paired cruises, 417 were caught between these depths, accounting for 77% of the specimens. Day and night distributions were similar during all three seasons, indicating that this species is a permanent, nonmigrating resident of these depths (Table 8).

In our sampling, S. diaphana has been captured in nets fished from the surface to 3500 m. The two specimens captured at the surface, both in late spring, were adults in poor condition, indicating that they may have been dead or dying. Beebe (1926) reported taking an S. diaphana at the surface off Bermuda, but commented that it was in very poor condition, being partially eaten by crabs. Günther (1887) also reported the capture of two specimens of S. diaphana at the surface near St. Thomas, Virgin Islands, but did not indicate their condition. It is unlikely that S. diaphana normally occurs in surface waters. Below 1000 m there were 10 discrete-depth captures. These probably were not the result of contamination from previous trawls, since in some cases the preceeding trawl was at a shallow depth where S. diaphana would not be expected. These captures probably represent some scattering of the species toward depths greater than 1000 m. Specimens were captured in open nets fished below 1550 m, but these probably were taken during the oblique portion of the tow as the net passed through their area of major concentration.

The 30 specimens taken in discrete-depth samples shallower than 400 m are considered contaminants from previous deeper tows, since in each case the tow capturing the specimens was immediately preceded by a tow to the depths where S. diaphana was normally taken in abundance. These shallow specimens include 1 postlarva, 6 juveniles, 8 subadults, and 14 adults. All were in samples from the upper 300 m, mostly at night (27 specimens), which is 100–500 m shallower than the next shallowest occurrence, and 300–400 m shallower than the major concentrations. Most (26 specimens) were taken in late spring (12) or late summer (14). If S. diaphana does occur in shallow water, it seems highly probable that such occurrences involve strays or unsound individuals.

Depth-size stratification exists in this species, with smaller individuals generally found shallower than large ones (Table 8). From 400–700 m 83 specimens were taken, the majority postlarvae and juveniles. Postlarvae were found primarily between 551 m and 750 m both day and night (Table 8). In winter, when postlarvae were most abundant, they formed the major portion of the catch from 601 m to 650 m, with a few captures as deep as 800 m. In late spring and late summer, most postlarvae were captured from 601–750 m. Juveniles were found primarily between 701 m and 850 m, slightly deeper than the postlarvae (Table 8). In winter, juveniles were very abundant, and the great majority were caught at the 801–850 m interval. At other seasons of the year juveniles were caught at similar depths. Subadults and adults of both sexes were found in greatest numbers at all seasons between 801 m and 950 m (Table 8), where they constituted the largest portion of the catch. There was no apparent stratification of these two stages.

The vertical distribution of S. diaphana, based solely on nondiscrete data, was described by Baird (1971) as being primarily between 401 and 1200 m, with the major concentration occurring from 701–900 m. Discrete-depth data from two areas of the eastern Atlantic indicate a depth range of 551–1000 m day and night (Badcock, 1970), and 501–900 m by day, 601–900 m at night (Badcock and Merrett, 1976). Thus our data are in close agreement with the previous literature.

PATCHINESS.—Patchiness of distribution does not appear to characterize S. diaphana. Three significant CD's were found. In winter, clumping was indicated at 650 m during the day and at 600 m at night, at which depths postlarvae were taken in greatest abundance. In late spring, there was clumping at 800 m during the day, involving juveniles, subadults, and adults in descending order of abundance; no clumping at night was indicated. In late summer, there was no indication of clumping. These data suggest that occasional aggregations may occur, but that distributions generally are random. Indications of clumping at the surface and at 150 m at night in late spring were disregarded, because they were believed to be based on either contaminants or dying specimens.

Beebe (1934) stated that sternoptychids (not necessarily Sternoptyx) observed from the bathysphere usually swam close together in groups of four or five, with occasional schools comprising up to 20 individuals. If such schooling characterizes Sternoptyx, then the schools may be presumed to be randomly distributed.

Barham (1970) observed that other sternoptychids were sometimes motionless and oriented horizontally, but that they went into a rapid, usually downward flight as the submersible approached. This suggests that larger sternoptychids may avoid the approaching net, so that, if aggregations occur, they are not adequately sampled.

NIGHT:DAY CATCH RATIOS.—The ratios of total night to day discrete-depth catch rates were slightly different from 1:1 in each season (Table 9). In winter and late spring, slightly more fish per unit effort were caught during the day, while in late summer slightly more fish per unit effort were caught at night. For each life history stage, however, there were considerable differences. Postlarvae were more abundant in night samples in late summer, slightly more abundant in day samples in late spring, and showed equal abundance in winter. Juveniles were more abundant in day samples in winter and in night samples in late spring, but had a 1:1 ratio in late summer. Subadults and adults reversed the juvenile trends in winter and late spring but also approached a 1:1 ratio in late summer.

No obvious explanation is evocable for the pattern of ratios. There is no correlation with patchiness (i.e., significant CD's, and differential diel net avoidance seems improbable. Either sampling was inadequate to indicate night:day equality, or avoidance behavior changes from season to season and according to life-history stage.

全球性種類，分布極廣。臺灣分布於東北、西南、東南部及東沙群島西南海域等海域。

一般以底拖網捕獲，不具食用經濟價值，通常做為下雜魚用。

中等大小的種類。鮮少超過50mm SL。D10﹔P 10﹔V 5﹔A 10-14﹔GR 7﹔脊椎骨29-30。軀幹寬，它的高通常稍微大於它的長。背刀上的棘長，它的長度大於或等於背鰭長。臀部發光器後的臀鰭支鰭骨短，臀上發光器位置約為小於#1ACA腹緣至體中線的一半距離。前頜骨短，上頜骨寬而長。齒小。較前面的鰓耙齒板有6個低矮的棘狀脊。後腹棘及臀部支鰭骨棘較此屬的其他種類短。銀色體表黑色色素比例較低，主要集中於頭部及背側形成側色素條，軀幹較亮；另外，尾鰭基部邊緣有寬帶。

大洋性中層魚類，成體無明顯的垂直迴游。一般生活於水深500-800公尺間。以橈腳類、端足類、介形蟲、磷蝦和小魚等為食。

Sternoptyx diaphana, the diaphanous hatchetfish, is a species of deep sea ray-finned fish in the family Sternoptychidae. It is the type species of the genus Sternoptyx, and was first described by the French naturalist Johann Hermann in Der Naturforscher 1781.

Feeds on copepods, ostracods, euphausiids, amphipods and fishes

Grand Bank to Brazil

Occasionally found in Canadian Atlantic waters. Found at depths of 500- 800 m.

nektonic

Known from seamounts and knolls