Unique Waterfall Climbing Cave Fish, by John Scott Moore

When asked to describe a typical fish, how would you describe it? First, you may say that it lives in water, then you might say it can only breathe in water, and finally, along with the first two, you may say that it lives entirely in water. For most fish, the above three characteristics are true, but what about those that aren’t your “typical” fish? There are fish that have adapted to live in very unconditional ways and in very unlikely environments. One fish that has adapted to an unconditional life in a seemingly uninhabitable place is the Waterfall Climbing Cave Fish (Cryptotora thamicola). The fish is a member of the river loaches or the family Balitoridae and is the only member of its genus Cryptotora (Discover Life). The Waterfall Climbing Cave Fish is only found deep within a few caves in Thailand and has many interesting characteristics (Kottelat 1988). The Waterfall Climbing Cave Fish has no eyes so it is blind, it has no scales, it is colorless, and potentially most interesting is its ability to climb rocks in the cave in which it lives. Other fish are able to survive without these adaptations, so why has the Waterfall Climbing Cave Fish evolved these defining characteristics and such a unique way of life? 

            In a world devoid of light such as in the depths of a cave, is the ability of sight truly necessary? The Waterfall Climbing Cave Fish is completely blind, but has evolved with the ability to find food and travel through its environment without having any ability of sight at all (Romero &  Paulson 2001). It is likely that the fish lost its ability of sight because it was unneeded in its environment, and since it was unnecessary, it was more beneficial to lose its eyes than have them and have no use for them. While it is still unclear how the Waterfall Climbing Cave Fish is able to maneuver in its environment and find food, it has fully adapted to living in caves totally blind and feeling its way through the environment.
 

Waterfall Climbing Cave Fish Cryptotora thamicola  Source

            The Waterfall Climbing Cave Fish is also devoid of both scales and most pigmentation (Kottelat 1988). The loss of pigmentation and the absence of scales is most likely due to the same reason that the eyes were lost, pigmentation and scales are just not necessary. Since they are blind, coloration in the Waterfall Climbing Cave Fish would not benefit in reproduction like it would in other fishes, so a loss of pigmentation doesn’t affect either the individual or the species in a way related to reproduction. There are also no, or very few, predators that would ever come into contact with the Waterfall Climbing Cave Fish, and because it doesn’t come into contact with predators there is no need for coloration to hide or camouflage the fish. The absence of scales may also be related to having no or very few predators. Without natural predators, it may not have ever been beneficial to the fish to develop scales. Another possibility for the lack of scales is that the added weight of scales would be detrimental to the survival of the fish. The addition of scales may also affect how the fish is able to move. Scales would likely impede the way the fish moves both in and out of water, therefore, it would not be beneficial to have ever developed scales. The absence of scales and pigmentation are likely due to the idea that they are just not needed, so there is no need to develop or retain something that is not beneficial. 

Pelvis of the Waterfall Climbing Cave Fish (c) Brooke E. Flammang

             The ability of the Waterfall Climbing Cave Fish to climb up rocks and through waterfalls may be its most unique adaptation. It is able to climb on rocks and in rapid flowing water due to its modified pelvic fins and pelvic girdle that is connected to the skeleton (Flammang et al.). The fish moves in a similar manner as a salamander by “walking” on its modified fins, and its pelvic girdle is morphologically similar to that of terrestrial animals (Flammang et al.). To see exactly how the fish walks and climbs within the cave, this short video describes how the fish is able to walk and provides an example of it “walking."

 

Pelvis of a salamander, specifically Eurycea longicauda  (Flammang et al. 2016)

 The Waterfall Climbing Cave Fish likely moves the way it does and climbs in order to reach new territories and to search for food.  By being able to cling to rocks and climb, it is able to reach other parts of the cave that other fish would not be able to get to. The Waterfall Climbing Cave Fish is also able to utilize the ability to climb to access new food sources such as algae on the less accessible rocks. The ability to walk and climb most likely evolved in the Waterfall Climbing Cave Fish in order to be able to colonize different areas of a cave and to feed on things on the cave walls. 

            The Waterfall Climbing Cave Fish has many unique and interesting characteristics. From the loss of its eyes and pigmentation, to the ability to climb on rocks and up waterfalls, the fish has a different plan for survival than most other fish species. Adapting and evolving to life in a cave underground is why the Waterfall Climbing Cave Fish has become so unique because a cave demands much more for survival than most other environments. Life for the Waterfall Climbing Cave Fish is strange, but it has ensured the survival of the species in an environment that very few other organisms could survive.

References

Discover Life.  2016

Flammang, B. Suvarnaraksha, A.  Markiewicz, J., and  Soares, D. 2016. Tetrapod-like pelvic girdle in a walking  cavefish. Scientific Reports 6: 23711. 

Kottelat, M. 1988. Two species of cavefishes from northern Thailand in the genera Nemacheilus and Homaloptera (Osteichthyes: Homalopteridae). Records of the Australian Museum 40(4): 225–231. 

Romero, A. Paulson, K. 2001. It’s a wonderful hypogean life: a guide to the troglomorphic fishes ofthe world. Environmental Biology of Fishes 62: 13–41.