In this blog post, we will answer the question “Are Starfish pets?” and learn more about the biology and care to have a starfish as a pet in a fish tank.
Are Starfish pets?
Yes, Starfish can be pets. We will now understand their origin and biology. Then we will learn about tank specificities to successfully raise a Starfish in your tank.
The phylum Echinodermata is composed of animals that live in the marine environment and the majority of its representatives have a body full of thorns or pointed projections. This characteristic was used to name the group, the term echinoderm is derived from Greek — echin means “covered with thorns”, and derma means “skin”.
Echinoderms are animals that live solely in the marine habitat. They are slow-moving, and some species are sessile. They do not form colonies and there are no parasitic species. Currently, about 7000 different species of echinoderms are known, among which we can highlight the starfish, sand dollars, and sea cucumbers.
Most of the Echinoderms have a spiny or verrucous appearance. They have an endoskeleton (internal skeleton) formed by calcareous plates, from which thorns or sharp projections often depart. The endoskeleton is covered by a thin epidermis.
The representatives of the echinoderms are triblastic organisms, that is, they have three embryonic leaflets: ectoderm, mesoderm and endoderm. In addition, they have coelom (body cavity lined with tissue derived from the mesoderm) and are deuterostomes (blastopore gives rise to the anus). The symmetry in these animals is different in the adult phase and the larval phase. While larvae have bilateral symmetry, in adults the symmetry is radial.
As triblastic, coelomate, and deuterostome organisms, Echinoderms are more related to the chordate phylum than to other groups of invertebrates. Another striking feature of echinoderms is the presence of an aquifer vascular system that relies on tube feet.
These animals do not have a head, therefore, their body does not have an anterior and posterior region, it is organized in an oral-aboral axis, the oral portion is the region where the mouth is located and the aboral portion in the region opposite to it.
The digestive system
The digestive system is complete in most species. A curiosity about Starfish is that they can evert their stomach and release digestive juices on their prey, initiating digestion externally. Afterwards, these animals recollect their stomach with the pre-digested food and finish the digestion internally.
The echinoderms do not have a specialized excretory system or a typical circulatory system, and the transport of substances is carried out through channels within the coelomatic cavity. Breathing is done by diffusion through the vascular system, in some species, and through gills, in others.
The nervous system
The nervous system of echinoderms consists of a nervous ring from which radial nerves derive. These animals have separate sexes, external fertilization and indirect development, with larval stages.
Aquifer vascular system
The aquifer vascular system, or the hydro vascular system, is unique to the echinoderms. It is composed of a network of channels filled with a fluid similar to seawater that differs by having cells, proteins and potassium ions. These channels branch through the animal’s body and have extensions called tube feet. This system is related to several processes, such as feeding and locomotion.
In Starfish, it is observed that this system is constituted by the madreporite sieve plate (a place through which water flows in and out of the echinoderm’s vascular system). This madreporite communicates with the circular channel. From the circular channel, which is located in the animal’s central disc, depart radial channels, which extend through the arms of the starfish. From the radial channels depart the lateral channels, which have a valve and end in an ampoule and a tube foot.
To guarantee movement, the tube system behaves like a hydraulic system. The tube foot elongates when the ampoule contracts and the water is forced into it and retracts when the muscles in the feet contract and force the water back into the ampoule. Tube feet, when they stretch, come into contact with the substrate and secrete chemical substances that allow them to adhere to the substrate. To release, non-stick substances are secreted.
Classification of echinoderms
Echinoderms can be divided into five classes
The most famous members of this group are the Starfish, which have a central disc and many arms. Typically, starfish have five arms, but some species can have up to 40. An important characteristic of these animals is their great capacity for regeneration. Through a single arm, for example, starfish can regenerate their entire body as long as part of the central disc remains attached to that arm.
The members of this group have a central disc from which long and flexible arms derive. Their movement occurs, mainly, by the action of these arms, which make movements similar to a snake.
The members of this group do not have arms, like the other echinoderms. The tube feet are arranged in five lines that allow these animals to travel very slowly. A striking feature in this group is the so-called Aristotle’s lantern, a scraper device present in sea urchins that are characterized by the presence of five limestone plates.
In these animals, the endoskeleton is reduced and their body is elongated. They have five rows of tube feet, and some of these structures are modified like tentacles around the mouth, helping these animals to feed.
They resemble small plants. Some representatives of this group live attached to the substrate (sea lilies), while others manage to crawl using their arms (sea feathers). The mouth of the crinoids is turned upwards, towards a region away from the substrate.
This class stands out because its representatives have a morphology that has changed little over time. Many fossils, from around 500 million years ago, show the similarity of these individuals to species that lived in the past.
What about the Starfish?
Now that we know the general characteristics of the group that the starfish belongs to, how about we learn more specific characteristics of Starfish?
Starfish occur in oceans all over the world, from the warm waters of the tropics to the polar waters, surviving both in the tidal zones of beaches and in regions of great depth, considered abyssal.
Although there are nearly 2000 species of Starfish, many people confuse other members of the Echinodermata phylum for individuals of the Asteroidea class. Taxonomically, the classes closer to Starfish would be the Ophiuroidea and Crinoidea, which include sea snakes and sea lilies, respectively. It is noteworthy that the presence of only five arms is not an obligatory feature, as some species of Starfish have more than 5 appendages attached to their central disk.
The digestive system of starfish is formed by the mouth, which is in the lower part of the body and closes with an oral sphincter, a small esophagus, the stomach with pyloric portions responsible for the storage and release of digestive enzymes, a short intestine, and the rectum connected to the anus that opens in the aboral portion of the animal.
Feeding habits vary widely among species of Starfish, with some being voracious predators that swallow their prey whole, while others evert a portion of their stomachs out of the body, digesting some of the food externally using digestive enzymes before internalizing the food. This strategy allows some Starfish to feed on animals larger than themselves, digesting their prey into tiny chunks that fit in their gut.
Large substrate predators
Importantly, most Starfish species are carnivorous, but many also feed on algae and suspended organic matter in water. As extremely skilled animals, Starfish commonly occupy the position of the top predator in the food webs in which they take part. Researchers have even recorded Starfish using their arms and the propulsion coming from the vascular system to open shells and other bivalves.
Without specific sensory organs or a defined brain, their nervous system is limited to a neural ring in the oral region and two main nerves associated with motor and sensory functions. Through groups of special cells, Starfish can detect differences in temperature, luminosity, gravitational orientation and chemical perception of particles in water.
Finally, Starfish are mostly dioicous, with adult individuals being male or female. When they reproduce, adults release gametes from their gonads directly into the environment. Fertilization is external in most Starfish species, with a few exceptions. Fertilized eggs can adhere to rocks or be carried by females, forming embryos that mostly go through a larval life stage (indirect development).
Starfish are also known to be able to perform asexual reproduction through the fission of their bodies. Each portion after cutting, if viable, is capable of regenerating itself. Thus, producing clones of the original individual. This same process also serves for bodily repairs, such as the regeneration of lost arms.
Can I raise a Starfish as a pet?
Yes, you definitely can raise a Starfish as a pet.
Starfish are fascinating animals because of their colours and ability to regenerate limbs or even the entire body. They can live for five to ten years if the right conditions are maintained in the aquarium. They need to live in a saltwater tank, where they can move around to look for food, and they will normally occupy the bottom of the tank.
You will need a 100-gallon aquarium or a larger one. It must contain full-spectrum lighting. Decorate the aquarium with stones and structures that mimic their natural habitat.
The water salinity level needs to be adjusted using a hydrometer to measure it. Salinity must be between 1.022 and 1.025 to make the environment similar to the starfish’s natural habitat. The water temperature must be between 71.6 and 77 degrees Fahrenheit.
Water changes are recommended weekly, total change between 10 to 15% of the water volume. It is also recommended the use of a quality pumping and filtration system.
Starfish are carnivorous and you can feed them with industrialized frozen food. Small starfish can eat mini algae as well. Foods for these animals are available at pet stores if needed. They need to be fed at least twice a week. Be careful to not overfeed them and “pollute” your water.
In this blog post, we answered the question “Are Starfish pets?” and learnt more about the biology and tank conditions to raise a Starfish as a pet.
Frequently Asked Questions (FAQs): Are Starfish pets?
How long does a starfish live in an aquarium?
They can live for five to ten years if the right conditions are maintained in the aquarium. Tank size, ideal food and water conditions are very important to prolong their life in captivity.
What do starfish eat?
Most Starfish are carnivorous and feed on molluscs (mussels and oysters), crustaceans (barnacles and armadillos), echinoderms (sea urchins and other stars), sponges, and corals
How does the regeneration process take place in the starfish organism?
Through stem cells in the animal’s body. They manage to recreate the lost organs from the beginning.
How do you know if a starfish is dead?
To determine if a Starfish is dead, you can feel its tube feet. The tube feet are the hundreds of cylindrical and empty structures beneath the Starfish. If they recoil at the touch of your finger, the Seastar is alive.
Are Starfish medicinal?
Starfish could be the key to treating some inflammatory diseases, such as asthma and arthritis. Researchers from the Scottish Association of Marine Sciences have found that the slimy substance that covers these organisms functions as a kind of “Teflon”, preventing the obstructing of blood vessels.
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Thao, N. P., Cuong, N. X., Luyen, B. T. T., Thanh, N. V., Nhiem, N. X., Koh, Y. S & Kim, Y. H. (2013). Anti-inflammatory asterosaponins from the starfish Astropecten monacanthus. Journal of natural products, 76(9), 1764-1770.