A Very Good Host: Parasitism

      The strange features of the Lophiiformes extends far beyond their feeding adaptations. While many fishes belonging to the order do have modified dorsal spines, other attributes are far more bizarre. Arguably the strangest looking of the fishes is found in the family Linophrynidae, consisting of 5 genera and 17 species (Pietsch, 1976).

Fig. 1 Soft Leftvent Angler (http://bit.ly/2p8jtPw)

Linophrynidae, or leftvent anglerfishes, appear much differently than other Lophiiformes. While they also have an illicium, it is short, broadened and its length is lesser than that of the esca (Kharin, 2007). Like Himantolophidae, or football fish, the left vent anglers have terminal papilla (Kharin, 2007), small lumps of dermal tissue found within the mouth. Enhancing the strange appearance, the fish have an ellipsoid body shape, rather than globular like many other Lophiiformes, compressed laterally with naked, unarmed black skin (Kharin, 2007). While they are noted to have black skin with a brown shine, the fish tend to appear nearly clear, with a black portion appearing to be almost internal (Fig 2).  

Fig. 2 Soft Leftvent Angler, Haplophryne mollis (http://bit.ly/2qHxGUG)

The fish are bathypelagic (Harte et al., 2008), meaning they inhabit the deep sea where the environment is dark and cold. Because of their preferred habitat type, little is known about the behaviours of the peculiar fish, but their method of reproduction is well studied. The male fishes, measuring much smaller than the females (Fig. 3), are parasites that attach to all known gravid females (Pietsch, 1976). The free-living linophrynid males display testes far less developed than in the parasitically attached males, and the attached males, with larger testes, contain a notable supply of spermatozoa (Pietsch, 1976).

Fig. 3 Close-up of the head of a preserved Soft Leftvent Angler, Haplophryne mollis, showing a tiny parasitic male attached to the top of her head (http://bit.ly/2qHxGUG)

Fig. 4 A tiny free-swimming male Soft Leftvent Angler, Haplophryne mollis, collected in the Sargoasso Sea (http://bit.ly/2qHxGUG)

The peculiarities of the fishes are bound to continue beyond what meets the eye, but research has not yet unveiled the other adaptations. Perhaps as research continues more information will be discovered, but, until then, only the strange appearance of the fishes can be certainly noticed as unique evolutionary adaptations.

References

Hartel, K., Kenaley, C., Galbraith, J. and Sutton, T. (2008). Additional Records of Deep-sea Fishes from off Greater New England. Northeastern Naturalist, [online] 15(3), pp.317-334. Available at: http://www.jstor.org/stable/pdf/25177116.pdf [Accessed 4 May 2017].

Kharin, V. (2007). Finding a rare species of leftvent seadevils Linophryne indica (Linophrynidae) near the Russian economic zone. Journal of Ichthyology, [online] 47(2), pp.198-200. Available at: http://bit.ly/2p7M6x3

 [Accessed 3 May 2017].

Pietsch, T. (1976). Dimorphism, Parasitism and Sex: Reproductive Strategies among Deepsea Ceratioid Anglerfishes. Copeia, [online] 1976(4), p.781. Available at: http://www.jstor.org/stable/pdf/1443462.pdf [Accessed 3 May 2017].

Fig. 1: Australian Museum (2010). Soft Leftvent Angler. [image] Available at: http://bit.ly/2p8jtPw [Accessed 4 May 2017].

Fig. 2: McGrouther, M. (2017). Soft Leftvent Angler, Haplophryne mollis. [image] Available at: http://bit.ly/2qHxGUG [Accessed 3 May 2017].

Fig. 3: Paul, D. (2017). Close-up of the head of a preserved Soft Leftvent Angler, Haplophryne mollis, showing a tiny parastic male attached to the top of her head. [image] Available at: http://bit.ly/2qHxGUG [Accessed 4 May 2017].

Fig. 4: Museum of Comparative Zoology, Harvard University (2017). A tiny free-swimming male Soft Leftvent Angler, Haplophryne mollis, collected in the Sargoasso Sea. [image] Available at: http://bit.ly/2qHxGUG [Accessed 4 May 2017].