The lateral line system is an important sensory organ in fish and is used to detect vibrations and movement in the surrounding water; this sense can be utilised in predator avoidance, schooling and prey detection. The lateral line runs down the side of a fish and comprises a series of sensory neuromasts, connected by tubules. Whilst some neuromasts remain below the dermis, at sections of the lateral line superficial neuromasts will be exposed to the outside environment via pores in the lateral line system.
Surrounding the pores of the lateral line system are the sharks' scales; unlike the scales of teleost fish sharks possess rough, placoid scales which (as well as being biologically similar to our teeth!) contribute to reducing drag whilst swimming and give sharks a rough, sandpaper like texture. The channelling of water over the neuromasts by the surrounding placoid scales will, of course, have an affect on the sensitivity of these sensory organs.
The fast swimming mako shark has a very different lifestyle to the spiny dogfish, which inhabits the ocean floor and has a much more sedentary lifestyle. The study found that the patterning of placoid scales around the neuromast pores in the mako shark may reduce turbulence in the water immediately surrounding the lateral line; this will affect lateral line sensitivity.
The arrangement of placoid scales around the neuromast pores in the spiny dogfish was entirely different, with S. acanthias exhibiting an entirely different divergent pattern to I. oxyrinchus. The placoid scales of I. oxyrinchus were orientated dorsally and ventrally from the pore, whilst those of S. acanthias were orientated exclusively ventrally away from the pore.
Whilst further research is required to fully analyse these differences across shark species, the results here suggest that the different lifestyles of these 2 shark species may be contributing to different sensory requirements in the lateral line and therefore different arrangement of the scales around the sensory organs.
Mckenzie, R. W., Motta, P. J. and Rohr, J. R. (2014), Comparative squamation of the lateral line canal pores in sharks. Journal of Fish Biology, 84: 1300–1311. doi: 10.1111/jfb.12353
