A Fin Day for a Walk Along the Substrate

     Anglerfishes are primarily known and praised for their natural fishing lures, or modified dorsal spines, that allow them to easily attract prey, but not every fish in the family offers the same features. Even without the use of bioluminescence to entice prey, the anglerfishes are remarkable and unique creatures. Among the most bizarre of these fishes, the family Brachionichthyidae, or handfishes, appear to be one of the most well-developed, but they experience higher predation rates than other anglerfishes.

Fig. 1 New handfish species walk on by (http://ab.co/2qusx6t)

The Brachionichthyidae family became known as handfishes because of their specialized fins, which allow them to walk along the substrate. The different species within the family vary from one fish to another, but all of the fishes have a small illicium of about 15 centimetres long located directly above the mouth that appears to serve no purpose (Pietsch, 2005). The benthic fishes reside in inshore waters at depths up to 60 metres (Pietsch, 2005), where the water temperatures are consistently low, and their skin is often covered in denticles (Last et al., 2007).

Fig. 2 Handfish from Tasmania, Australia - fish that walk (http://bit.ly/2q4QYGQ)

      Handfishes are amongst the first Australian fishes named (Last et al., 2007) and are restricted to inshore marine habitats off southern Australia, mostly inhabiting Tasmania (Pietsch, 2005). Certain species, like the spotted handfish Brachionichthys hisrsutus, are endemic to south Australian estuaries, with an exceptionally limited distribution (Roberts and Hawkins, 1999). 

     The fish was discovered off Tasmania by a French Explorer named Francois Peron in the early 19^th century and is now considered endangered due to its low population (Last et al., 2007). Their limited presence within the seas is likely caused by the high level of predation the fishes experience, which has been brought on strongly by the starfish species Asterias amurensis (Roberts and Hawkins, 1999). A. amurensis, introduced from Japan, has been feeding on the egg clusters left behind by the handfishes, driving the fishes into the brink of extinction (Roberts and Hawkins, 1999).  

Fig. 3 Asterias amurensis (http://bit.ly/2pBNQPv)

      Although handfishes have a well-developed mode of locomotion, and appear better evolved than the many other fishes that opt to walk along the substrate, their population is strongly threatened. Because of their struggle to remain present in the ocean, the advantages of their evolutionary adaptations is often questioned, with scientists often claiming that their selected features are in no way increasing the rate of survival, or viability. 

Fig. 4 A female Spotted Handfish, Brachionichthys hirsutus, with fully developed embryos (http://fishesofaustralia.net.au/home/species/2842)

References 

Last, P., Gledhill, D. and Holmes, B. (2007). A new handfish, Brachionichthys australis sp. nov. (Lophiiformes: Brachionichthyidae), with a redescription of the critically endangered spotted handfish, B. hirsutus (Lacepède). Zootaxa, [online] pp.53-68. Available at: http://mapress.com/zootaxa/2007f/z01666p068f.pdf [Accessed 11 May 2017].

Pietsch, T. (2005). Brachionichthyidae. Handfishes, warty anglerfishes, [online] 9. Available at: http://tolweb.org/Brachionichthys [Accessed 11 May 2017].

Roberts, C. and Hawkins, J. (1999). Extinction risk in the sea. Trends in Ecology & Evolution, [online] 14(6), pp.241-246. Available at: http://www.sciencedirect.com/science/article/pii/S0169534798015845 [Accessed 11 May 2017].

Fig. 1: Gowlett-Holmes, K. (2010). New handfish species walk on by. [image] Available at: http://ab.co/2qusx6t [Accessed 11 May 2017].

Fig. 2: Baron, M. (2012). Handfish from Tasmania, Australia - fish that walk. [video] Available at: http://bit.ly/2q4QYGQ [Accessed 11 May 2017].

Fig. 3: Watson, J. (2009). Asterias amurensis. [image] Available at: 

http://bit.ly/2pBNQPv [Accessed 11 May 2017].

Fig. 4: Green, M. (2017). A female Spotted Handfish, Brachionichthys hirsutus, with fully developed embryos. [image] Available at: http://fishesofaustralia.net.au/home/species/2842 [Accessed 11 May 2017].