Parasitism is a form of symbiosis where the parasite benefits at the expense of the host organism. Most organisms have some kind of parasite associated with them, and reef animals are no different. When we have a problem, we go to the dentist or medical doctor (or some people prefer non-traditional healers), but what do reef animals do? For most of them, there is no real solution, but for fish there is. There is a group of organisms that have become specialized on cleaning parasites off fish, and this blog will introduce you to those present in the UNBC Reef Tank.
There are two cleaner organisms in the UNBC Reef Tank, a cleaner shrimp, Lysmata amboinensis (De Man) (Decapoda: Hippolytidae), which has a number of common names (northern cleaner shrimp, scarlet cleaner shrimp, skunk cleaner shrimp, Pacific cleaner shrimp), but is usually simply referred to as cleaner shrimp in the reef tank trade. There are two specimens in the tank, and this is the result of an apparently hard-wired tendency that leads to only a monogamous pair of shrimp remaining at any one cleaning station (Wong and Michiels 2011). I purchased three, but the third shrimp vanished in short order after introduction. You can find them behind the anemones at the right hand side of the tank. Incidentally, this seems to be a dangerous place as the shrimp are not immune to the sting of the anemone. If their antennae touch an anemone tentacles, they have to pull to free it – watch if one comes out and you may be able to see this. At feeding time, they will venture out from behind the anemone rocks to catch whatever morsels they can find, because they are really scavengers, i.e., their cleaning habit is facultative. If you look carefully, you may see that each individual frequently carries 20 or so large, greenish eggs under her abdomen, so they must be females. Yes, but both of them are also male, because they are protandrous simultaneous hermaphrodites (Bauer 2000). This means that all are born male, but develop female reproductive organs as they mature, although some specimens apparently remain male only (Lin and Zhang 2001). To make matters even more complicated, they can serve as males at any time, even when brooding eggs, but can only serve as females shortly after a molt!
In nature, or in the presence of larger fish, they normally position themselves in a cave or under an overhang. They have bright, contrasting white and red colours, and long white antennae, which advertises their presence to passing fish. Fish will come in to these stations to get cleaned, i.e., parasites and food remnants removed from their mouth, and this is where it gets interesting. Even fish that eat other types of shrimp, will not eat the cleaner shrimp. Instead they will keep their mouth open, and the shrimp will enter and pick off the offending items. They will also pick items off the skin of the fish, gaining food whereas the fish will get rid of parasites or food remnants.
There are a number of species of so-called cleaner shrimps in several families. A previous occupant of the UNBC Reef Tank was the banded coral shrimp, Stenopus hispidus , (Decapoda: Stenopodidae), which is really a small lobster rather than a shrimp, and consequently armed with some fairly impressive pincers.
The second member of the cleaning crew in the UNBC Reef Tank is the sharknose cleaner goby, Elacatinus evelynae (Böhlke & Robins) (Family Gobiidae), also represented by two specimens. These small fish are from the Caribbean, where they live in pairs at cleaning stations. The relationship with their host fish appears to depend on the parasite load in the area, so that when load is low, the gobies cheat by feeding on host fish tissue (Cheney and Côté 2005). In the UNBC Reef Tank, the gobies take food when other fish are being fed, but they also appear to take advantage of the mayhem to clean the other fish at that point. Generally they seem to approach other fish from the side – I have never seen them at the business end( the mouth) of another fish. Their pectoral fins are modified so they function like suction cups, allowing these fish to hang upside down under a coral or on the glass of the aquarium.
There are a number of other species of cleaner gobies, and many are available in the reef aquarium trade. More familiar to the general public is the bluestreak cleaner wrasse, Labroides dimidiatus (Valenciennes) (Labridae), which also is available in the trade from time to time. This species has a reputation as being difficult to keep alive, however, but like the cleaner goby, it is a facultative cleaner that also cheats by feeding on host tissues, as well as taking other food items (Grutter 1997). Unlike the gobies, cleaner wrasses perform an elaborate dance in front of hosts, which then will remain still with their mouth and gill covers wide open if they accept the cleaner.
Cleaner stations are often occupied by several species of cleaners, working together on hosts arriving for service. But why are the diminutive cleaners not eaten by their often predatory guests? It appears that certain colour patterns and size signal to potential customers what is a cleaner and what isn’t (Stummer et al. 2004). There are several models, but certain stripes and colours appear to be convergent factors.
Bauer, RT. 2000. Simultaneous hermaphroditism in caridean shrimps: a unique and puzzling sexual system in the Decapoda. Journal of Crustacean Biology, 20(Special Number 2): 110-128
Cheney, KL, and IM Côté. 2005. Mutualism or parasitism? The variable outcome of cleaning symbioses. Biology Letters, 1: 162-165
Grutter, AS. 1997. Size-selective predation by the cleaner fish Labroides dimidiatus. Journal of Fish Biology 50: 1303–1308
Lin, J, and D Zhang. 2001. Reproduction in a simultaneous hermaphroditic shrimp, Lysmata wurdemanni: any two will do? Marine Biology, 139: 1155-1158
Stummer, LE, JA Weller, ML Johnson, and IM Côté. 2004. Size and stripes: how fish clients recognize cleaners. Animal Behaviour, 68: 145–150
Wong, JWY, and NK Michiels. 2011. Control of social monogamy through aggression in a hermaphroditic shrimp. Frontiers in Zoology, 8:30.