Mariana snailfish, Mariana hadal snailfish
Pseudoliparis swirei, the Mariana snailfish or Mariana hadal snailfish, is a species of snailfish found at hadal depths in the Mariana Trench in the western Pacific Ocean. It is known from a depth range of 6,198–8,076 m (20,335–26,496 ft), including a capture at 7,966 m (26,135 ft), which is possibly the record for a fish caught on the seafloor. Various anatomical, physiological, molecular and genetic adaptions help this species survive in such depths.
This pale, tadpole-like fish reaches up to 28.8 cm (11.3 in) in standard length and 160 g (0.35 lb) in weight. It is apparently the top predator along certain stretches of the Mariana Trench, feeding on tiny crustaceans in a deep-water habitat with few larger predators. Pseudoliparis swirei are abundant in their deep-sea habitat and lay relatively large eggs that are almost 1 cm (0.4 in) in diameter.
Pseudoliparis swirei is named for Herbert Swire, the First Navigating Sub-Lieutenant of HMS Challenger and author of The Voyage of the Challenger, a personal narrative of the historic circumnavigation of the globe in the years 1872-1876. In 1876 the expedition found the Challenger Deep, habitat of the Mariana snailfish.
A study of females showed that mature eggs are unusually large, up to 9.4 mm (0.37 in) in diameter. In total, there were up to 23 mature eggs for each female (each larger than 5 mm or 0.20 in in diameter), which were alternated with immature, small eggs, the number of which was about 850. Eggs of intermediate size were rarely seen. Even in the largest eggs, no structures were found that indicate the development of the embryo within the eggs. There are indications that the larvae of P. swirei and at least some other hadal fish spend time in the open water at relatively shallow depths, less than 1,000 m (3,300 ft).
