Fish aren’t traditionally perceived as having personalities, but they’re anything but the dumb automatons that our ancestors would have us believe.
Underwater organisms don’t have the facial musculature that we as primates have evolved. Quite simply they haven’t needed it, therefore they haven’t acquired it through natural selection. However they have been evolving and surviving on this planet for over 500 million years.
And they do communicate to each other.
How do fish sense each other?
In a Darwinian world where survival is paramount, the lateral line has become their first defense and sensory organ. This first level of communicating allows the individual to feel what’s around it. The layer of sensory cells that run along the flanks of most fish, detect the pressure changes in the surrounding environment. This system has evolved to the point where fish react with an almost simultaneous motion to an external stimulus.
How do fish school in such dense numbers without colliding?
Fish have a sensory barrier around them, a kind of bubble that they can perceive. This bubble is squashed as objects or animals move around the individuals perception. They can sense their immediate surroundings in this fashion.
Some fish such as the freshwater knife-fish even generate electric fields. These fields are influenced by their surroundings, especially other animals, and the knife-fish react to that reflection of their own electric field and use it to locate prey.
Sharks have an extremely sensitive network of electroreceptors that can detect the smallest electric fields from other animals.
Vision is also important in the depths of the ocean especially in the upper Euphotic zone (where photosynthesis can occur). Most of the longer, lower energy wavelengths are lost quickly, absorbed by the water column. Red light disappears first, then orange, then yellow… leaving only blue as you descend to the furthest depths of the Photic zone (The depth that light can penetrate through water).
How do fish display their intentions?
Contrast over actual color makes a big difference at depth and aquatic animals can use that to their advantage to display their intentions. Humbolt squid for example can change their entire body from red to white and back like you can flick a light switch. They do this at depths far beyond red light can be seen (200m-700m) so appear in this twilight world as if they are going from black to white like individual morse code signals. What they are saying to each other is beyond our understanding.
Closer to the surface we have fish species that utilize many more frequencies of the electromagnetic spectrum including the ultraviolet wavelengths.
On a more day to day scenario, most SCUBA Divers and snorkelers who pay attention will have noticed that some species of reef fish can have drastically different colourations. Take the Big eye crescent tail as an example.
When it’s calm an individual will be a deep red, when stressed it can bleach to a silver. Similarly when fish such as the Big-nose Unicornfish visit cleaning stations they can display complex patterning only for it to fade to black once the fish swims away.
When fish think about sex
During spawning aggregations many fish species undergo drastic color changes that signal their readiness to participate. The bumphead parrotfish are pretty obvious during their aggregation as their heads bleach white from the usual green.
In the Caribbean, Nassau groupers migrate in groups to their annual spawning grounds and are often led by an individual who sports a drastically different body patterning. Once at the spawning site they all adopt an even more extreme color change. For further reading see this article.
Bohar Snappers have a variety of different colorations during their spawning aggregations, sometimes two small white spots appear on their dorsal area, others adopt a bleached blue hue rather than their usual russet red. Others adopt a mixture of the two with a red belly, a white stripe down their flanks and a bluish dorsal area. As I pour over the many spawning rushes I’ve filmed of this species I cannot see any distinguishable pattern in whether a female adopts a certain body color prior to her egg releasing rush. A pattern may emerge after further observations though.
See this clip of a small group interacting in preparation for spawning. The female with the broken dorsal fin is being nudged by a number of males. Maybe this nudging is meant to initiate her egg releasing rush. Maybe it’s the males trying to ascertain if she is ready or not….?
For a really in depth look at this behavior and other similar color changes seen during spawning, Tony Wu has written an excellent series of articles that are well worth a read.
Additional articles and films of Palau’s spawning aggregations can be found here.
Communication between species
It has been shown that fish communicate between species. In the case of the Grouper and Moray Eel, the Grouper will shake it’s head next to the Eel to signal an intention to start hunting. The strategy has been shown to be more successful at catching prey.
Underwater acoustics in fish
Underwater acoustics is not just the tool of marine mammals, many fish are also extremely vocal. Have you ever swum over a reef and heard all the clicking noises? This is a medley of fish and crustaceans each with their own message. Usually the message is “this is my territory, keep out”. Sound is an extremely useful form of communication in the aquatic environment as sound travels much further than light. A fish can remain hidden whilst letting an intruder know that it’s encroaching. Groupers often growl or rumble from within their hiding place. The behavior across a multitude of species was documented here and demonstrates the rich complexity in coral reefs.
So in conclusion, whilst fish and other aquatic organisms like cephalopods might not be able to convey their intentions through facial cues like we can, they are extremely in tune with and aware of their environment. They are able to send messages that even other species can understand. The fact that we might not be able to understand them is perhaps our failure rather than theirs.
Have you had any interesting interactions with aquatic wildlife? I’ve not begun to get started with the marine mammals here, whole different kettle…..so there’s still a load more to talk about. Feel free to leave a comment in the section below. Do you know the difference between a head nod and a shake in Moray Eels, can you predict when a Stingray is about to lift up and depart from it’s resting place? So many more topics and examples for the future.
For more info on filming underwater and learning about your subjects this article may well be helpful.
Until next time, Cheers!
The evolution and development of vertebrate lateral line electroreceptors