In the marine aquarium, symbiotic relationships play an important role. Generally, they fall under three categories: mutualism, commensalism, and parasitism.
Spotted rare shrimp (Periclimenes yucatanicus) forms close symbiotic relationships with several species of sea anemone. It waves its long antennae to attract client fishes and then cleans ectoparasites from the mouth and gill coverings of the passing fish.
Ants and Acacia Trees
In an aquarium, a good symbiotic relationship is one that benefits both organisms without adversely impacting the other. This is called commensalism and is common in nature. For example, young crabs can live inside jellyfish for protection and food. However, this does not harm the jellyfish and only benefits the crab. Another good example is the symbiotic relationship between pistol shrimp and goby fish. Pistol shrimp has poor eyesight, so the goby fish becomes his companion, watching out for predators and letting him know of potential threats by flickering his tail. The goby also stirs up the sand to make sure the burrow is safe, and they spend most of their time together with the shrimp’s head sticking out to keep an eye on things.
An aquarium with a healthy mix of fish and plants will benefit from the addition of some natural elements. Mosses such as Java moss (Vesicularia dubyana) look great around rockwork and tied to hardscape in the background, while stem plants like Ludwigia repens and Ludwigia arcuata can provide color around rocks and in the midground. Floating plants such as common duckweed (Lemna minor) and Riccia fluitans can add interest to the water surface.
Adding some acacias to the tank is a great idea as well, because the whistling thorn (Vachellia drepanolobium) trees have an important symbiotic relationship with ants. This unique interaction deters grazing by large herbivores such as elephants and giraffes.
A recent study published in Science Advances found that acacias rely on ant-mediated nutrient uptake to maintain their reproductive success and health. The researchers found that acacias lacking ants were not able to grow as vigorously or produce as many seeds, and they also showed an increase in bacterial load. In the study, the scientists found that acacias partner with multiple sets of ants over time, each partnership fitting their needs at a given stage of growth.
For your aquarium, this means you should keep an eye on the nitrate levels and use quality filtration to maintain them below the toxic level. Feed your shrimp high-quality fish flakes or pellets, high-protein powdered baby shrimp food and algae wafers, and leave some old aquatic plant leaves to keep the nitrates low.
Sharks and Remoras
One of the most famous symbiotic relationships in nature is that between sharks and remoras. Remora fish are able to travel to different parts of the sea without having to burn energy by attaching themselves to the underside of sharks. They also get to eat scraps of food that the sharks leave behind. While this association can be considered mutualism, it has been speculated that remoras may actually have negative fitness consequences for some shark hosts.
This is why it’s important to remember that a symbiotic relationship can only be categorised as either mutualism or parasitism. It is impossible to say whether an interaction between sharks and remoras is commensalism or parasitism unless there are robust quantitative data regarding net fitness consequences to both the remoras and the sharks.
There are a number of factors that may complicate shark-remora interactions and make it difficult to categorize them as either mutualism or parasitism. For example, some remoras may have to swim more often when traveling with sharks because of the sharks’ greater propulsion requirements. Moreover, the sharks may sometimes use their fins to knock off remoras that are attached to them.
Other sharks might be more tolerant of remoras, such as the bull shark (Carcharhinus leucas). Bull sharks have a very strong and stable attachment to their remoras. This allows remoras to rest more comfortably and enables the sharks to feed on smaller prey species while the remoras keep the surrounding waters clean by eating parasites and dead skin.
Sharks and remoras also often associate with animals other than sharks, such as manta rays, whale sharks, sea turtles, and dolphins. Although these associations are less well-characterized than the association with sharks, they can be described as either mutualism or parasitism.
Another type of symbiotic association that can be observed in your home aquarium is that between gobie fish and pistol shrimp. These symbiotic pair-ups are very common in the wild, where the fish act as vigilant guards of their shrimp partners’ burrows. In addition, the shrimp protect the fish from symbiont bacteria that would otherwise inhibit their ability to digest foods.
Goby Fish and Pistol Shrimp
Pistol shrimps and goby fish form a unique friendship that is well worth witnessing. They are both excellent predators, but they also need each other for survival. Pistol shrimps are a very social species and live in pairs, usually with a mate. They also build burrows underneath rocks and within sea sponges, where they can be quite safe from larger predators. In fact, whole colonies of these shrimps, up to 350 individuals, have been seen living together in such sea sponges.
Like many other crustaceans, pistol shrimps have poor eyesight but excellent excavating skills. They are obsessed with building and maintaining their burrows and can spend up to half of each day inside them. During this time they are constantly shifting rubble and debris from the entrance of their burrow in order to keep it clear. In the wild, they associate with goby fish of the genus Alpheus. This symbiotic relationship is an example of commensalism, in which both partners benefit from their association. The gobies act as early warning systems for the pistol shrimp, whose poor eyesight makes it impossible for them to detect danger on their own. In return, the pistol shrimps provide a safe home for their goby companions and protection from predators.
In the wild, the symbiotic association between pistol shrimps and gobies is not only an excellent example of commensalism, but it has also helped scientists better understand how different species can co-exist in an ecosystem. In 1957, junior scientist Luther Christian put a pair of these shrimps and gobies into a small aquarium and found that they maintained their unique partnership.
This is a very easy symbiotic relationship to recreate in your own aquarium. Pistol shrimps can be housed with almost any goby species as long as they have a similar diet and aquarium set up. The only thing to be careful about is choosing a tankmate for the pistol shrimps that will not out-compete them in their hunt for food. For this reason, it is best to keep them with other crustaceans rather than any larger fish species.
Corals and Fish
There are many examples of symbiotic relationships between fish and corals in our marine aquariums, but there are also some interesting symbiotic relationships between fish and other invertebrates that are not corals. One example is the symbiotic relationship between the clownfish and the sea anemone. Clownfishes appoint sea anemones as their host species, and the anemone provides protection from predators by stinging them with its tentacles when necessary.
Another interesting symbiotic relationship is between the pistol shrimp and the goby fish, wherein both the pistol shrimp and the watchman goby benefit from their symbiotic relationship. The pistol shrimp has very poor eyesight, and so it relies on the goby to keep an eye out for any potential predators. The goby keeps a close eye on the pistol shrimp, and it will flick its tail to warn the shrimp when a potential predator is in close proximity. The pistol shrimp will then retreat into its burrow where it can remain safe from the potential predator.
Interestingly, the symbiotic relationship between the pistol shrimp and the goby fish is an example of inquilism, which is a type of commensalism that is more intimate than endoecism. Inquilism involves sharing a refuge and can be seen in animals such as hacklefish that follow tiger sharks to feed on the leftovers from the tiger’s kill or tree frogs that share shelter with ants.
In the case of sexy shrimp and the sea anemone, the sexy shrimp benefits from the anemone’s protection from predators by stinging them when they come too close. The anemone, in turn, benefits from the sexy shrimp by removing parasites that can infect its gills, mouth and eyes.
In your shrimp aquarium, a good way to encourage this symbiotic relationship is to provide a hardscape that the shrimp can use for hiding and as a place where they can show off. A great option for this is a group of finely-patterned granite stones clustered together to resemble boulders or mountains, with smaller matching pieces of gravel acting as “fallen rocks” at their base. Then, for driftwood, try to find pieces with lots of fine details and gnarled areas, such as long twigs that stretch across the tank.
