The sea ​​urchin fishPorcupine fish, also known as porcupine fish, are fascinating and unique animals in the world of marine aquariums. Their unique appearance, characterized by a body covered in spines transformed from their scales, their defensive technique, and their territorial behavior, make them a highly appreciated and respected species both in the wild and in aquariums. In this article, we will delve into the Characteristics, behavior, defense techniques, feeding, captive care, aquarium parameters, and important considerations for their maintenance, integrating all the relevant and detailed aspects that may interest you if you want to know them in depth or keep one in your marine aquarium.
Morphological characteristics and defense system of sea urchin fish
La main characteristic of sea urchin fish It is the presence of a multitude of thorns that cover its entire body. These spines, derived from the transformation of scales, remain folded when the animal is calm, but bristle menacingly when it senses danger, thanks to its ability to swell and triple its size by ingesting water or air. This defense mechanism is extremely effective in deterring predators, as it makes it difficult to swallow and very dangerous prey.
Belonging to the family Diodontidae, porcupine fish have a typically globose or egg-shaped body, with large and prominent eyes, an appearance that makes them similar to puffer fish (family Tetraodontidae), although they are usually larger size and their bone structure is more robust. Within the Diodontidae family, there are approximately 15 species, distributed across two main genera: Diodon y Chilomycterus. Some species, such as Diodon hystrix, can reach up to 90 cm in length, which places them among the largest spiny fish in tropical and temperate waters.
One of the most striking morphological peculiarities is the absence of pelvic fins, which partially limits its maneuverability and control, favoring the evolution of its elaborate defensive strategy. Its beak-like mouth is another significant adaptation: it allows it to easily break the shells of the invertebrates it normally feeds on.
Distribution, habitat and most common species
The sea ​​urchin fish have wide distribution It covers all the planet's tropical and subtropical seas, also present in some temperate zones. They prefer rocky bottoms and coral reefs, where they can find refuge in crevices and caves, and they seek their favorite food among crustaceans and other hard-shelled invertebrates. To better understand their ecological importance, you can consult our article on the Large release of sea urchins in Xábia to restore marine ecosystems.
The most well-known and commonly kept species in aquariums include:
- Chilomycterus schoepfiThe striped porcupinefish, which grows to 30 cm in the wild, although in aquariums it rarely grows larger. It is one of the species least likely to swell when threatened.
- Chilomycterus antennatus: Popularly known as the antenna urchin fish, it is smaller (up to 12 cm), peaceful and recommended for aquarium keeping.
- Diodon holocanthus: Called the porcupine angelfish, it can grow to over 30 cm and is famous for its striking appearance. If you'd like to learn about more curious species, visit our section the rarest fish in the world.
- Diodon hystrix: The common porcupinefish, only suitable for public aquariums due to its large size, reaching up to 90 cm in the natural environment.
- Diodon liturosus: With an attractive livery characterized by black ocelli and white outlines.
La reproduction The reproduction of sea urchin fish is pelagic: they release eggs into plankton-rich ocean currents, from which the larvae emerge, which later settle to the bottom and evolve into their adult form. They do not exhibit sexual dimorphism, so it is impossible to distinguish males from females with the naked eye. This type of reproduction explains their global dispersion and also the impossibility of breeding them in captivity, since the conditions for larval breeding in aquariums cannot be adequately reproduced.
Behavior, territoriality and coexistence
El social behavior The nature of sea urchin fishes presents important nuances. While in the wild they tend to maintain a rather solitary behavior, in captivity they can show curious recognition behaviors toward their caretaker, associating their presence with the opportunity to feed. Despite being sociable animals, they show a strong territoriality towards specimens of similar size or morphology, such as other porcupine fish, puffer fish or boxfish, so it is not recommended to put several individuals of similar species in the same tank.
Under normal conditions, porcupinefish maintain a peaceful, though reserved, attitude and rarely develop aggressive behavior toward other unrelated species. However, when they feel threatened or cornered, they can spectacularly deploy their spines and release, through the mucous membrane that covers their skin, a toxic substance or toxic mucusThis chemical compound, very similar to that secreted by boxfish, is designed to repel predators, but in a closed environment like an aquarium, it can be highly harmful to the rest of the tank's inhabitants, even causing mass deaths of other fish if action is not taken quickly.
Therefore, before introducing a sea urchin into your aquarium, it is essential to consider species compatibility and its ability to release toxins under extreme stress. In exceptional situations, and if the presence of toxins is detected, it is advisable to transfer the remaining fish. de peces to another aquarium and perform a complete water change to restore the environment. These episodes are not common, but can occur if the animal feels threatened or mishandled.
Feeding: natural and captive diet
La diet of sea urchin fish It is omnivorous, with a clear preference for hard-shelled invertebrates, especially crustaceans and mollusks. They use their powerful, horny-structured, parrot-like beak-tooth to easily crush shells and access the soft parts of the animal. For this reason, it is absolutely Coexistence with mobile ornamental invertebrates is incompatible, such as crabs, shrimp, snails or small mollusks, as they will be identified as food and quickly devoured.
In their natural habitat, they also consume small fish, worms, and occasionally plant matter. In captivity, porcupinefish are very voracious and accept virtually any type of food:
- Shellfish and crustaceans whole (shrimp, mussel, clam)
- Pieces of white fish
- Frozen food or seafood and fish purees
- Granules or sticks specifically for carnivorous marine fish
It is highly recommended to offer them bivalves and shelled crustaceans, since the wear and tear caused by biting the beak is essential to prevent excessive growth of this organ, a disorder that can make feeding difficult and cause health problems. For more ideas, you can also check out our article on other species. other exotic species such as the razorfish.
Despite their voracity, porcupine fish They are not compatible with aquariums full of invertebrates. and reef, but should be kept in tanks where the decor consists primarily of live rock or synthetic elements. Keeping them in aquariums with other species of similar size and calm temperament is the best option.
Water parameters and optimal aquarium conditions
Sea urchin fish, given their adaptation to tropical and subtropical environments, require a very precise water conditions to ensure your well-being and prevent disease:
- Minimum aquarium volumeIdeally no less than 300 liters for adult specimens, although for large species a tank of 500 liters or more may be necessary.
- Temperature: Between 25 and 28 ºC, maintaining stability within this range.
- Density (salinity): Between 1.020 and 1.024 for tropical water species, preferably stable.
- pH: Between 8 and 8,4, avoiding pronounced fluctuations.
- Carbonate level (KH): Above 7 dKH to promote skeletal health and spine maintenance.
- Calcium and magnesium concentrations: Optimum calcium levels of 400 to 450 ppm and magnesium between 1300 and 1350 ppm, similar to those recommended for corals.
- Nitrogen compounds: Zero presence of ammonia and nitrites, and very low nitrate concentrations, ideally less than 20 ppm. Porcupinefish are very sensitive to nitrogen imbalances.
La filtration must be oversized and supported by a high-performance skimmer, since the voracity of these fish can cause a rapid increase in organic waste. It is recommended to perform water changes of 20-25% every two weeks to maintain the quality and stability of the aquatic environment.
On the other hand, it is important to remember that porcupine fish, despite their general robustness, They can develop bacterial diseases and exophthalmia (protrusion of the eyeballs) if the water conditions are unsuitable, and may even lead to vision loss. The key to preventing these problems is rigorous water quality management and regular observation of the animal.
Care and responsible management in aquariophilia
El maintenance de peces sea ​​urchin in captivity It requires a series of prior considerations to ensure its well-being and that of the rest of the aquarium's inhabitants:
- Do not introduce them into aquariums with mobile invertebrates or other spiny fish of the same family.
- Avoid excessive handling and stress: Trying to capture them can cause bloating and the release of dangerous toxins.
- Monitor beak development: regularly offer hard-shelled prey to ensure proper wear.
- Monitor nitrogen compound levels and perform frequent maintenance.
- Ensure shelter areas with structured live rock, avoiding sharp or unstable decorations that could harm the fish or cause it to knock over items when inflated.
Furthermore, it's important to keep in mind that porcupinefish don't exhibit sexual dimorphism, they can't be easily sexed, and therefore, captive breeding hasn't been possible due to the difficulties of raising planktonic larvae. All commercial specimens are wild-caught, an ethical reason to value the commitment and responsibility when acquiring one.
Peculiarities of the defense system: thorns and toxins
The sea urchin's defense system is one of the most sophisticated in aquatic fauna, combining the physical action of its spines with a chemical response. When the animal feels threatened:
- It absorbs water (or air on the surface) and swells to triple its size, raising its spines and becoming practically impossible for most predators to swallow.
- It releases toxic mucus through its skin, a chemical compound that repels potential enemies and can cause acute toxicity to other fish in closed tanks.
This dual technique allows it to survive against predators much larger in size. swollen state can be maintained for long periods, and although it reduces its maneuverability, it does not completely negate it, allowing the fish to slowly move away from the danger zone while keeping its defenses activated.
In the domestic environment, this mechanism should be understood as an extreme stress response. Owners should avoid situations that may lead to this: avoid handling the fish unnecessarily, provide safe shelters, and avoid cohabitation with other potentially conflictive species.
Sea urchin fish are species of great ecological and ornamental value, endowed with unparalleled beauty and defense mechanisms. While they can adapt well to life in captivity and even recognize their owners, they require a spacious environment, strict water parameters, and a varied diet that allows for proper beak wear. Their ability to release toxins under extremely stressful circumstances requires careful selection of tank mates and close environmental monitoring. Keeping one of these specimens is a considerable responsibility, but also a very enriching experience for the dedicated aquarist.
