Fish Communication

Fish Communication

     As a kid I used to stare at the fish tank in my house and think the fish were talking to each other when their mouths moved. I used to wonder what they were saying, stories they were telling each other. I would even make up some conversations. Eventually I grew out of believing that fish could talk. But I always knew that even if they weren’t actually speaking, they were still in fact communicating in some way. But the question was-How?



     Schools of fish communicate using pheromones. Pheromones are endogenous chemical signals secreted by organisms. They trigger an innate response in other members of the same species. The behaviors that are influenced by pheromones are sexual attraction, territorial demarcation, signaling alarm, and recruiting members together for feeding or defense purposes. “Some aquatic organisms may only respond to chemical cues during times of the day. Migratory adult sea lamprey are nocturnal and respond to migratory pheromones at night” (Johnson & Weiming, 2010). In some cases the communication reflects more than just the survival and reproduction of an individual organism, but also contributes to others in the species. Alarm substance pheromones are pheromones that alert and warn other group members of a nearby predator. Some fish species release a volatile substance when attacked by a predator that can trigger a flight response in members of the same species of fish. Pheromones are detected by the olfactory systems. These systems for detecting pheromones include olfactory sensory neurons, which are nerve cells with one end exposed to the external environment, often embedding in an otherwise impermeable skin or cuticle.



     “Experience and learning also alter behavioral responses of fishes to alarm substances. Several fish species exhibit learned predator recognition to alarm substances” (Johnson & Weiming, 2010). Minnows, which are small fresh water fish that belong to the carp family, are known to shoal in large numbers or schools. Their small size makes them easy prey for all the carnivorous fish and they rely on their speed and close shoaling habits to save them from predators. Minnows can react very quickly to danger signals. They release an alarm pheromone stored in specialized cells on its skin only when the skin is damaged, warning other minnows in the school that a predator has attacked. The flight response will cause the school of minnows to disperse in a frantic manner, then school up and gradually swim away from the source of the alarm pheromone. But not all schooling fish have traits of the flight response.

     In some cases different species that can produce alarm pheromones can pick up each other’s version of it so that if one fish of a different species is attacked other species in the area know to get away from the area. There have also been fish that once used the pheromone, but lost the ability to produce and detect it because it would interfere with their diet which consists of similar species, which is the case for piranha. “Some species undergo an ontogenetic shift where alarm substance responses are only elicited in young age groups, likely due to trade-offs between foraging and predation risk” (Johnson & Weiming, 2010).  It is said that alarm substance pheromones evolved for three main reasons. The first reason is that it came as a way to ensure survival of members of the same fish species because it warns them of the presence of a predator. They may have also evolved as a way to prevent fish from eating their own species, more specifically their offspring. If a fish bit a member of the same species it would have the same effect of them as if it was released from a fish under attack from a predator. The third possible reason for the alarm substance pheromone is that it has been recently hypothesized that predator fish have begun to be able to pick up the presence of the pheromone attracting them to injure fish and an easy meal. But as the number of predators in the area around an injured fish increases, so does the time it takes from first strike to until the time of ingestion. This allows the prey more time to free itself and possibly escape. Whatever the reason, pheromones are a vital part of a fish species survival.

     Knowing that pheromones play a huge part in the lives of fish species it makes me wonder about the age old argument of instinct versus intelligence. Can fish think or is everything solely based on nature’s cues passed down from generation to generation? Since evolution plays a huge role on a fish’s instincts, it has to affect fish species intelligence as well.

Works Cited

Johnson, N., & Weiming, L. (2010, October). Understanding behavioral responses of fish to pheromones in natural freshwater enviroments. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural & Behavioral Physiology, pp.701-711. Retrieved February 23, 2012, from the Complete Academic Database

Great White Sharks

Great White Sharks

     I remember my favorite move as a child. It wasn’t a typical cartoon movie like most children love watching, I never liked those. My favorite movie was the American thriller Jaws. Most kids my age, and adults were terrified by Jaws but I was fascinated by the movie. I would sit and watch in awe. I couldn’t believe a fish could be so big and powerful. I wanted the shark to be my pet. Even to this day, 20 years later, my mother still jokes about how I loved to watch Jaws, but I was afraid of the movie Star Wars. She found it amusing that I wasn’t afraid of a movie that was based on a real animal that could quite possibly cause the damage that the great white shark did in real life. That was where my fascination with sharks started. The great white shark is probably the most known shark out of the entire species, but still so little is known about them.



     Every year the Discovery Channel has there highly anticipated “Shark Week” where they broadcast shows all about sharks. Every year they always air a show with massive adult great white sharks jumping out of the ocean while they hunt seals. But out of all of the shows they never show any juvenile great whites. I can’t recall ever seeing any information on them and it made me wonder, where are the baby great white sharks? So little is known about great white sharks. “Even basic notions, such as how large they actually grow, how long they live, how many are out there, and where they go to breed and pup, remain a mystery” (Cillican, 2011).

     Recently off Port Stephens, New South Wales, a great white shark nursery was discovered. Scientists discovered the nursery from a YouTube video entitled “Great White Shark Hunters”. Even though the video shows the illegal hunting of great white shark pups, scientists gained a lot of knowledge from the video. “Australia listed the great white as protected in 1999; internationally it is listed as vulnerable on the IUCN (World Conservation Union) Red List for Threatened Species, and it was also banned for trade by the Convention on International Trade in Endangered Species of Wild Fauna and Flora in 2004” (Cillican, 2011). Because of the video, scientists have begun to research the area. They found that the nursery area consists of a 50 kilometer stretch of broken coastline between Seal Rocks and Stockton Beach. This location is perfect for a shark nursery because the nutrient-rich conditions of the area attract schools of Australian salmon, mulloway, mullet and snapper, which are the favored meals of juvenile great white sharks. Scientists from the CSIRO laboratories began tagging juvenile sharks in the area in 2007. “The team has fixed a satellite tag to the shark’s dorsal fin, which records the date and time, water temperature, depth and light levels” (Cillican, 2011). Acoustic tags have also been surgically implanted into the shark’s abdomen. The tags transmit a unique number when the shark swims within 500 meters of an underwater acoustic listening station, which have been scattered throughout Australian waters. They have also started annual helicopter surveys of the nursery to estimate how many sharks migrate there.

     “Conservation and study around this juvenile shark crèche is vital-knowledge from the nursery could help hint at the health of future adult populations” (Cillican, 2011). The research taking place at and around the Port Stephens nursery is important in helping protect a species that many people probably never realized was endangered. About 120 sharks are killed every year due to the bay catch of commercial and recreational fishing. This is a crucial amount because great white sharks only give birth to 2-14 pups in a litter and only produce 4-6 litters in a lifetime.

     Making people aware of this situation is the first step in conserving one of the ocean’s most powerful and most vulnerable creatures. Most powerful because they are one of the sea’s greatest hunters, and most vulnerable because their numbers are so few compared to other species of sharks. This type of research is a window into the great white shark’s world. The more we know about them, the more we as humans can do to make sure that our actions don’t impose on their habitats or threaten their well-being. Our actions impact everything that goes on in the ocean. Our responsibility with that type of power is the key to their survival.

Works Cited

Cillican, J. (2011, Dec). Great white creche. Australian Geographic, pp.80-85. Retrieved March 3,2012,from the Academic Search Complete Database.