Chemical communication in fish – what pheromones say
Most fish have a highly developed sense of smell, so it is not surprising that chemical communication through pheromones can be important for many species. This applies especially to fish with poorly developed eyesight, e.g. catfish.
Mysterious pheromones
The chemical communication of fish is based on poorly known substances such as pheromones. It is undoubtedly certain that small amounts of these compounds are sufficient to cause an immediate reaction in a fish of the same species when released into the water. Chemical communication using pheromones is a very common phenomenon among fish and aquatic organisms in general. Using pheromones, fish can inform each other of danger, readiness to spawn, willingness to find mates, identify sex or belonging to their species, to repel potential enemies, and communicate within a school and between parents and their offspring. It is likely that pheromones also play a role in way finding for anadromous fish that swim from saltwater to rivers and streams to spawn in them.
Sexual selection
In the process of reproduction, pheromones allow fish to properly identify their spawning partner. Tests for this were carried out on two species, closely related cichlids from Lake Malawi. Researchers were testing the senses of the femalePseudotropheus emmiltosused to select the right male. To make her task more difficult, in addition to a partner from her own species, she had at her disposal a male of a related species Pseudotropheus fainzilberi. With full contact, the female always chose the male from her species. When she had only eye contact with the males, she got confused and chose Pseudotropheus fainzilberi male as well. However, when scent contact was added to eye contact (water between tanks was mixed) the female almost unerringly selected the male of her species. That means that the chemical factor plays a very important role in sexual selection in these fish.
Synchronization of reproduction cells release
The synchronization of reproduction cell release becomes particularly important in aquatic environments. In the vast majority of fish, external fertilization occurs, so egg-laying and milt secretion must occur at the same time and place, otherwise the water will quickly move the reproductive cells away from each other. A well-studied example of synchronization of reproduction cell release is the mating period in Atlantic herring. Males secrete a pheromone during the release of milt that causes females to release eggs.
Identification of individuals
Chemicals secreted by fish can also be used to identify a particular individual. Ictalurus natalisa member of the catfish family, has this ability. Not only does it distinguish individuals based on smell, but it also “sees” their positions in the hierarchy. The sense of smell is also used by some cichlids to identify their offspring at the time when they take care of them.
The smell of fear
The ability to communicate about the danger using a chemical substance is also a very intriguing ability. For this reason, there are cells in the epidermal cells of fish that produce substances known as alarm pheromones or Schreckstoff. These ingredients are released into the water when the skin is damaged. When the information contained in this signal reaches representatives of the same species, or related species, it triggers a reaction in them to allow them to avoid attack. It turns out that chemical communication often performs much better compared to auditory communication, visual or tactile.
Characteristics of different signals
| Features of signals | Visual signals | Tactile signals | Audible signals | Chemical signals |
| Maximum range | average | very short | long | very long |
| Speed of information exchange | high | high | high | average |
| Ability to avoid obstacles | poor | poor | good | very good |
| Locating the source | good | good | average | variable |
| Energy expenditure | low | low | high | low |
| Chronology of appearance | late | early | late | originally |
| Potential information capacity | high | low | high | very high |
Source: Aleksander Kołodziejczyk
Scientists assume that this mode of communication is used by most living organisms. The problem, however, lies in the detection of pheromones. Because they are generally mixtures of different chemical compounds. Moreover, they are species-specific, but their composition within a species may vary depending on, for example, season, species occurrence, diet, etc.
Ph.D.Eng Aleksandra Kwaśniak-Płacheta
Literature
Kołodziejczyk A., Feromony, https://slideplayer.pl/slide/417898/.
Moyle P. i inni (2004), Fishes an introduction to ichthyology, Prentice Hall.
Plenderleith M. i inni (2005), Female preference for conspecific males based on olfactory cues in a Lake Malawi cichlid fish., Biology Letters.,1, 411-414.
