Fish – Navigation in an Extra Dimension

Fish exist in a completely different environment than humans. Although humans can jump or sit on the ground, we don’t have the ability to naturally fly, meaning we don’t traditionally think in terms of navigating up or down. However, fish in a body of water not only swim forwards, backwards, left, and right. They regularly swim up and down in the water. If you have a fish tank, you’ve probably seen some of your fish swimming at different levels or depths of water. In today’s blog post, we’ll be taking a look at some different methods of fish navigation.

A possible method fish may be using to determine their relative depth is sensing hydrostatic pressure (Holbrook and Burt de Perera 2010). Hydrostatic pressure is defined as pressure exerted by fluid at a specific point within the fluid due to gravity. Hydrostatic pressure increases as depth increases, as larger amounts of fluid weigh more. This is the reason why humans can only dive so deep without needing to be in a submarine; the hydrostatic pressure would crush us. In the case of aquatic creatures, only those that are highly adapted to the pressure can live on the ocean floor. So how can fish use this ability to tell where they are? The answer may lie in the fish’s swim bladder, a gas filled organ found in fish that allows them to control how buoyant they are. Fish may be able to sense the rate of pressure change by measuring the change in their swim bladder’s volume, along with their speed (Holbrook and Burt de Perera 2010). This allows the fish to determine where they are on the vertical plane and ties into their overall ability to navigate.

Another method fish use to navigate is geometric information. This is most applicable to fish kept in tanks or bowls, as they are able to use the rectangular or spherical shape of their container to determine where they are. However, the type of tank a fish is raised in can actually affect its ability to use geometric information for navigation (Brown et al 2007). Fish typically use geometric cues when there are no other features or landmarks to their tank. However, when features do exist in their tank, they use both the features and the geometric cues to navigate. Fish raised in a spherical bowl as opposed to a rectangular tank use geometric cues significantly less often, showing that exposure to different shapes and angles at an early age has a clear effect on a fish’s ability to navigate.

Not only do adult fish have to navigate in the water, their larvae must do it too. Reef fish larvae need to stay close to their reef for protection against predators. Some reef larvae, specifically those of the families Pomacentridae and Apogonidae, have been shown to use olfactory cues in order to find their reef and stay close to it (Paris et al 2013). These reef fish larvae can smell “reef odor” coming from “odor plumes” in water currents from several kilometers away, and change not only their direction towards the reef, but also their swimming speed in order to reach the reef faster. Some larvae, particularly those of damselfish, can even determine where the crest of the reef is through olfactory cues alone. Unfortunately, if olfactory cues play such a strong part in fish larvae navigation, they could be severely affected by ocean pollution and acidification.

Sadly, as with most other navigation topics, there was little to no information about the neural basis of fish navigation readily available. Although the behavioral base seems to be well understood, studies of fish navigation would benefit from a focus on brain structure, which could tell us more about how the fish are actually processing the information they receive.

Sources:

Brown, Alisha A., et al. “Growing in Circles: Rearing Environment Alters Spatial Navigation in Fish.” PsycEXTRA Dataset, 2007, doi:10.1037/e603982013-031.

Paris, Claire B., et al. “Reef Odor: A Wake Up Call for Navigation in Reef Fish Larvae.” PLoS ONE, vol. 8, no. 8, 2013, doi:10.1371/journal.pone.0072808.

Holbrook, Robert I, and Theresa Burt De Perera. “Fish Navigation in the Vertical Dimension: Can Fish Use Hydrostatic Pressure to Determine Depth?” Fish and Fisheries, vol. 12, no. 4, 2010, pp. 370–379., doi:10.1111/j.1467-2979.2010.00399.x.

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