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NMFRI Gdynia Aquarium

Fish

  • Banded archerfish

    Banded archerfish

    Order: Perciformes
    Rodzina: Toxotidae

    Toxotes jaculatrix

    This species is found in Indo-Pacific waters, from India, through Southeast Asia, Indonesia, Philippines, New Guinea to Australia. It tolerates  changes in salinity, so it can be found in fresh, brackish and salt waters. However, it prefers the brackish waters of the mangrove forests, but also lives in small streams and rivers, as well as near vegetation on coral reefs.

    It is a calm fish that lives in small flocks just below or near the surface of the water. If the fish is left without a group, it becomes aggressive towards other fish. The maximum length of the Banded archerfish’s body is 30 cm, however, they usually grow up to 25 cm. In captivity, they reach a smaller body size, about 16 cm and can live from 5 to 8 years, and sometimes even 10. Its body is oblong and raised from the back. The body is generally silver-white, although it may also be yellow. The back is green-olive or brown. The dorsal fin is yellow-green, the caudal fin is earthy green, and the anal fin is silver. On the sides of the body there are wide, black stripes (4 or 5), which shorten as the fish ages. Juveniles have a silver body with a yellow-green or brown back. The archerfish’s eyes are large and set so that he can look forward.

    It is omnivorous, the basis of its diet are land insects, molluscs, crustaceans, small fish and plants. Actively hunts its prey by shooting insects on the vegetation above the water surface with a stream of water spewed from the mouth.

    It can shoot an insect from a distance of 1.25 meters, and larger specimens are able to hit the victim from a distance of 2-3 meters. It is able to reach the victim within 50 milliseconds after it hits the water. It can also jump above the water and catch an insect on the fly.

    It is a dioecious, oviparous animal with external fertilization. The first reproduction occurs when the animal is 10 cm long. During spawning, which takes place in November and December, the female lays between 20,000 and 150,000 eggs, with fertility closely related to the size of the female. They rarely reproduce in captivity. They plays insignificant role in commercial fishing, but are also caught as an aquarium fish.

    Indian shooter – sniper fish

    The archerfish can see a clear picture despite the different refractive index on the water-air interface. It does this through special adaptations in the eye with an extremely large retina on which the image focuses. This allows the fish to look through the water into the air without having to take into account the distortions in the spatial system, resulting from different refractive indexes, and give an accurate shot. Another possible way how a shooter deals with minimizing refractive indices is to position itself almost directly under its prey before the shot, then it sees the same picture he would see from the air.

    The way it shoots its victim is also important, unfortunately it is not known in detail. It is known that a shooter is able to spit water by exerting pressure in the mouth. A stream of water is generated in a tube formed from the tongue hooked on the groove in the palate. Water is thrown out of the mouth by high pressure due to the contraction of the gill chamber. The length of the water stream shot by the fish can reach up to 3 meters.

  • Copperband butterflyfish

    Copperband butterflyfish

    Order: Perciformes

    Family: Chaetodontidae

    Chelmon rostratus

    This species occurs from the Andaman Sea, through the Indo-Malay region, to Japan and the Great Barrier Reef in the Pacific Ocean. It inhabits coastal reefs, rocky shores and estuaries at depths from 1 to 25 m. The Copperband butterflyfish swims alone or in pairs. Juveniles are loners and inhabit shallow waters. It is an active fish, which swims freely, but also spends time hidden in cracks and crevices where it lies motionless. It is not aggressive, but will defend its territory against other representatives of the genus Chelmon. It reaches small dimensions, the maximum total length is 20 cm, while in captivity it is much smaller. The maximum reported age from the environment was 10 years, while in captivity it lives up to 4 years.

    Its body has the shape of a shield with a long protruding muzzle ending with small snout. Its coloration is also characteristic, on the silvery-white body there are 4 vertical stripes in yellow or orange with black and white edges.

    At the base of the dorsal fin is a false eye with a bluish-white circle. The dark eye of the fish is much smaller than the false eye.

    Young individuals are similar to mature ones, only their false eye is larger in size and the stripes are more intense. It is a carnivore. It uses his long mouth to get food out of the cracks. Its diet is based on polychaetes, representatives of corals such as Aiptasia, molluscs and crustaceans. The Copperband butterflyfish is dioecious and monogamous. During spawning taking place just below the water surface, the female lays eggs, which are fertilized by the male. Fertilized eggs float along with currents in the water column. The larvae lead is planktonic.

    Due to its attractive appearance, the pensetnik is a popular aquarium fish. Nevertheless, it is a fish that requires experience, because it is difficult to keep it alive in captivity. Individuals smaller than 14 cm are most often sold, juveniles not exceeding 3 cm in length are very rare. The Copperband butterflyfish is exported from the Philippines, Indonesia and Australia, while individuals caught in Australia are considered more adapted to life in captivity, which is why they achieve a double price. This is due to the methods of obtaining individuals from the natural environment.

    Mimicry – a form of defense against predators.

    The Copperband butterflyfish due to its small body size can easily fall victim to larger predators. Like other gentle fish, it has developed a false eye to mislead the opponent. The false eye, i.e. a colorful spot located on the dorsal fin, is a form of mimicry, i.e. similar to other dangerous animals. In the Copperband butterflyfish, the false eye, which is much larger than the real eye of the fish, is designed to mislead the predator as to the location of the fish’s head. In most cases, the predator attacks the head so that the victim has no chance of escape. If the predator considers the false eye, and thus the back of the fish’s body, as its head, such a fish has a chance to escape. A similar strategy is used by many species of marine fish, but also freshwater, such as the Oscar.

  • Green spot mandarin

    Green spot mandarin

    Order: Perciformes

    Rodzina: Callionymidae

    Synchiropus splendidus

    This species is found in the tropical waters of the Indo-West Pacific, from the Philippines and Eastern Indonesia to Northern Australia. It is a bottom fish associated with coral reefs. He prefers coastal reefs and shallow lagoons with a sandy base, where he settles on sand or rocks, most often among coral branches, where he finds food and shelter. Occurs to a depth of 20 meters. This slow and shy fish is most often found in small groups or in pairs. It reaches a small body size, with a maximum length of 7 cm. Males are slightly larger than females.

    The Green spot mandarin is distinguished by its unusual and intense color. The body is light green or olive and is decorated with a combination of black, orange and blue spots. The first ray of the dorsal fin is elongated in the male. The mandarin skin is covered with a thick layer of mucus, which has an unpleasant smell and a bitter taste. Its task is to inhibit many types of parasitic infections and minimize the risk of infection after physical injury. There is also a layer of cells on the skin that produce and release substances with some toxins. It is suspected that this secretion is used as a repellent to predators and other fish. Also, most likely, its bright coloration is supposed to inform predators that it is poisonous. Mandarin feeds during the day. Its diet consists mainly of copepods. In addition, it feeds on algae, plankton and small benthic invertebrates. It is a dioecious fish. Fertilization occurs when the male and female swim close together. Eggs and larvae are pelagic. When the larva reaches the appropriate developmental stage it settles to the bottom. This species breeds successfully in captivity. Due to its attractive coloration, it is a valuable aquarium fish. Fishing for mandarins as aquarium fish plays an important role in the local economies of the Philippines and Indonesia.

    The Green spot mandarin – is this an optical illusion like in the case of the Regal blue tang?

    The Green spot mandarin is one of two species of vertebrate whose blue color is due to the presence of cyanophores in the skin. Cyanophores are dye cells containing a blue dye. Cyanophores are also present in another representative of the mandarins – Synchiropus splendidus (magnificent mandarin). In other fish, the blue color is structural in nature and is a light phenomenon in which light-reflecting pigment cells (isidophores) participate.

     

  • Red piranha

    Red piranha

    Order: Characiformes

    Family: Serrasalmidae

    Pygocentrus nattereri

    This species of freshwater fish is common in South America, where it occurs in the rivers of Argentina, Brazil, Bolivia, Colombia, Ecuador, Guyana, Paraguay, Peru, Uruguay and Venezuela. It lives in the warm waters of several major rivers, such as the Amazon, Paraguay, Parana and Essequibo, as well as in many smaller ones. It prefers rivers rich in mineral substances that give the water a white color, only sporadically seen in rivers with a very low pH and high content of humic and fulvic acids, whose waters are black. The Red piranha inhabits coves, floodplains, lakes, streams and large rivers, up to a depth of 20 meters.

    It grows up to a maximum length of 50 cm, but rarely exceeds 35 cm, and a maximum weight of 3.9 kg. It is characterized by a deep, laterally compressed body with long dorsal fins. The coloration varies depending on the geographical location and age of the fish. Mature individuals have a gray-silver body with a reddish-orange belly. The dorsal, anal and caudal fins are black, while the pectoral and abdominal fins are red-orange. Juveniles, on the other hand, have a silver body with dark spots, which disappear gradually as the fish grows.

    It lives in groups of about 20-30 fish. Interestingly, they do not group to hunt for large victims collectively, but for protection against larger predators. However, provoked or starving, they can go into a feeding spree, then several groups of piranhas gather around the victim and eat it within a few minutes.

    Such attacks are extremely rare. Despite the opinion of a dangerous predator, it is omnivorous. A typical diet of red piranha includes insects, molluscs, crustaceans and other fish, as well as plants and carrion. The feeding time varies depending on the size of the fish. Smaller fish search for food during the day, while larger ones feed at dawn and late afternoon and evening. Usually hunts waiting for prey hidden among the vegetation, but can also actively pursue prey. Its powerful teeth can cause serious bites.

    The Red piranha is not a migratory species, but travels in search of conditions favorable for reproduction and spawning during periods of increased rainfall. It is a dioecious animal. The male can be distinguished from the female by the cross-sectional shape of the abdomen. In males it has the shape of the letter “V”, while in females “U”. In addition, the female belly has a slightly deeper shade of red. Piranha has two breeding seasons per year that are associated with water level fluctuations. When the individual is ready for sexual activity, it loses its red color and selects spawning habitat such as vegetation floodplains. This animal shows breeding behavior around nesting sites, then two different sexes swim side by side being in close contact with the abdominal sides. Initially, they were thought to be courtship, but this behavior was to defend the nest. The nests are about 4-5 cm deep, 15 cm in diameter and are dug among grass. The female lays up to 5000 eggs, which she sticks to the vegetation in the nest. After a few days of fertilization, how are young individuals hatching who seek shelter from predators among the vegetation. Juveniles will reach puberty after one year.

    The Red piranha is considered one of the more dangerous and aggressive species of piranha, but it has developed a kind of symbiotic relationship with another piranha agent – Serrasalmus marginatus, which cleanses its body of parasites. It can be dangerous to people due to the risk of biting. It is the most commonly caught species of piranha used commercially as aquarium fish. Its fishing and trade as an aquarium animal can locally reduce the number of this species.

    Fish and children don’t have a say – do they?

    The Red piranhas can communicate with each other. Very often the issuing of sounds manifests itself along with aggressive behaviors, such as biting, racing or fighting. The sounds produced by piranhas are generated by muscle spasms and are associated with a swim bladder that serves as a resonator. When removed from the water, piranha makes a drumming-like sound. Three other types of sounds are made in the aquatic environment and vary in frequency and duration depending on the circumstances. They will be different when two individuals meet, before a fight or during a pursuit or just before a bite. Almost all sounds made by piranhas are produced in the context of social interaction. Low sound is usually produced during moderate attacks, while loud, high sounds are generated during more energetic attacks.

  • Selene

    Selene

    Order: Perciformes

    Family: Carangidae

    Selene vomer

    This fish inhabits the marine and brackish waters along the west Atlantic coast from Maine to Uruguay, including the Gulf of Mexico and Bermuda. It occurs in coastal waters with a hard or sandy bottom, at a depth of 1 to 53 meters. Juveniles prefer estuary areas or swim freely along sandy beaches. Selene is a pelagic fish, it actively swims in the depths of the water, but it can also be associated with the bottom. It can live in large shoals, in smaller groups or in pairs. It grows up to 50 cm in length, although the average length is 35 cm and weigh is over 2 kg. Due to its body shape and color, it is called a moon fish. Its body is tall and short, strongly flattened to the sides. The head profile is very steep and straight, angular at the top. The mouth is set low with the lower jaw sticking out and the eyes are high. Due to the location of its eyes, it keeps looking down when it is swimming in search of food. The body appears to be devoid of scales as they are very small, thin, transparent and embedded in the skin of the fish. The dorsal and anal fins have a characteristic appearance, in which the second ray is much longer than the others and gives the fin the shape of a scythe. Coloration is fairly uniform, usually silvery with a bluish tinge on the back. Sometimes it can also be aquamarine, turquoise or orange, and the edges are pale green-yellow. The juvenile has a few weak vertical stripes that disappear as it grows, and its first two fin rays are elongated and look like threads. Selene is a migratory predator that feeds on small benthic invertebrates, shrimps, small crabs and fish. It is a dioecious animal that is relatively poorly studied and little is known about its early developmental stages. The female lays eggs which are then fertilized by the male. After external fertilization, pelagic larvae hatch from the eggs. Selene does not look after offspring. It is not widely caught, but its meat tastes great. It is much more often wanted as an aquarium fish due to its interesting shape and attractive appearance.

    How to effectively camouflage yourself in water?

    Avoiding predators in the open ocean is difficult as there are no objects to hide behind. Then the silver surface of the fish plays an important role in the camouflage. The stealth system bends polarized sunlight on the animal. There are guanine crystals in the skin of selene, which have a high refractive index and reflect them by adjusting the light scattering to the angle of its incidence. Guanine crystals are arranged in the skin so as to coincide with the main axes of the fish, then regardless of the position of the animal in the water column, they will reflect the sun’s rays. This will make the fish invisible to predators. The skin of the fish is also silver for the human eye, but when we look at it under a microscope at higher magnification, it turns out to be a multicolored mosaic of yellow, orange, green and bluish-violet colors.

  • Pinecone soldierfish

    Pinecone soldierfish

    Order: Beryciformes

    Family: Holocentridae

    Myripristis murdjan

    This species occurs in the tropical Indo-Pacific waters from the Red Sea and East Africa through Indonesia and Papua New Guinea to Samoa, north to the Marshall Islands, Taiwan and Ryukyu Islands and south to the east and west coasts of Australia. It inhabits coral reefs, both seas and lagoons. It is a fish associated with the bottom living near caves or rock crevices, where it can hide during the day. Most often it occurs to a depth of 10 meters, but it can also be found at a depth of 50 meters.

    The Pinecone soldierfish can grow up to a maximum length of 60 cm, but the vast majority have a length of 18 to 25 cm. Its hallmark is red body color, large scales and large bulging eyes. The color may vary slightly between individuals from red to dark red with a dark band running from the top of the gill cover to the base of the pectoral fin, and the edges of the scales are reddish brown. The body is covered with chenoidal (comb-like) scales similar to a rectangle with comb-shaped teeth on the back edge. The scales have a rough surface, and there are also sharp protrusions on the body of the fish. Above the pupil is a large black spot, while below a smaller spot, which looks like a black vertical band passing through the center of the eye. The first pectoral fin on the spines and is usually folded along the body of the fish. It has a red color, like the other fins, but others have additional white leading rays. The second dorsal fin is soft and in shape and location corresponds to the anal fin.

    The Pinecone soldierfish is active at night, then it feeds mainly on plankton, such as crab larvae. There are no obvious differences between males and females. It is oviparous, fertilization is external, and eggs and planktonic larvae. Juveniles reach sexual maturity after reaching an appropriate body length, which is 11 cm for females and 7 cm for males.

    Due to the poor quality of the meat, they are not caught for consumption, but their appearance makes them interesting enough to be caught as aquarium fish.

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