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Choosing Wrasses That Eat Zooplankton

Learn how your zooplankton-feeding wrasses eat and what you should feed them in your aquarium.

By Scott W. Michael |

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Paleontologists tell us that about 100 million years ago, the seas were home to some unusual plankton-feeding fish. These were not the huge modern-day cartilaginous fishes (basking sharks, whale sharks, manta and mobula rays) that eat zooplankton, but they were giant bony fish of the family Pachycormidae. 


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Some of these toothless giants attained a maximum length of more than 30 feet and fed by filtering tiny plankton from their oceanic environment.

 

While these leviathans have long gone extinct, there are many small bony fish that feed on zooplankton around modern coral reefs. One group that has a number of representatives in this feeding guild is the family Labridae, which are commonly known as wrasses. In fact, some of the most colorful and sought-after plankton-feeding fish belong to the labrid clan.


The creole wrasse (Clepticus parrae) exhibits anatomical characteristics seen in many zooplankton-feeders, including a body and fins that indicate that it is built for speed. Photo by Scott W. Michael

The Plankton

Before we go any further, we need to briefly examine plankton. This group of organisms is defined as plants and animals that drift in the water column. In some cases, they are very small — but not in all cases. In fact, plankton can be broken down into one of seven different categories based on size (the smallest are the femtoplankton, and the largest are the megaplankton). Those plant (i.e., algae) species that occupy this niche are referred to as phytoplankton, while drifting animals are referred to as zooplankton. Those planktors that drift in the upper layers of the water column are referred to as pelagic plankton (e.g., salps), while those that live nearer (but not on) the seafloor are referred to as demersal plankton (e.g., certain mysid shrimp).


Most of the razorfishes feed on bottom-dwelling invertebrates, but the green razorfish (Xyrichtys splendens) is an oddball that feeds mainly on zooplankton. Photo by Scott W. Michael

When it comes to plankton-feeders, two strategies are recognized. There are fish that filter-feed, meaning that they nonselectively strain plankton from the water column. The second group (to which all the zooplankton-feeding labrids belong) contains those that are plankton-pickers; these selectively target and ingest individual planktors from the water column.

The Wrasses

Most of the 470-odd species of wrasse feed on benthic invertebrates. Most have pronounced canines used for grasping and strong pharyngeal teeth for masticating larger prey items. Even those labrids that feed off the seafloor will opportunistically feed on zooplankton — if there is a sudden influx of planktors available (e.g., fish eggs), they will consume them. There are also wrasses like the blackedge thicklip wrasse (Hemigymnus melapterus) that feed on zooplankton when young but shift to bottom-dwelling invertebrates as they grow larger.

 

However, I wish to concentrate on those labrids that feed primarily on zooplankton as adults. The genera that fall into this category are:
• fairy wrasses (Cirrhilabrus)
• creole wrasses (Clepticus)
• Connie’s wrasse (Conniella)
• minute wrasses (Minilabrus)
• flasher wrasses (Paracheilinus)
• false coris (Pseudocoris)

Other genera include one or more "black sheep” that feed heavily on zooplankton. These species include:
    •    painted wrasse (Halichoeres pictus)
    •    green razorfish (Xyrichtys  splendens)
    •    sixline wrasse (Pseudocheilinus hexataenia)
    •    fourline wrasse (P. tetrataenia)
    •    belted ribbon wrasse (Stethojulis balteata)
    •    redspot ribbon wrasse (S. bandanensis)
    •    three ribbon wrasse (S. strigiventer)
    •    three-lined ribbon wrasse (S. trilineata)
    •    blunthead wrasse (Thalassoma amblycephalum)
    •    bluehead wrasse (T. bifasciatum)
    •    sixbar wrasse (T. hardwicke)
    •    Cortez rainbow wrasse (T. lucasanum)
    •    Brazilian wrasse (T. noronhanum)

Females and juveniles of a number of other Thalassoma species will feed heavily on zooplankton. Many of these species augment their zooplankton diet with a variety of smaller, benthic invertebrates, as well.

Some wrasses swim high in the water column to feed on pelagic zooplankton (e.g., Walindi fairy wrasse, Cirrhilabrus walindi; Cortez rainbow wrasse, T. lucasanum), while there are other labrids (e.g., ribbon wrasses, Stethojulis spp.) that feed on demersal zooplankton. Those zooplanktivores that feed away from the reef are more vulnerable to reef piscivores.

Lined fairy wrasse
Zooplankton-feeding wrasses, such as this lined fairy wrasse (Cirrhilabrus lineatus), are the best members of the family for the reef aquarium. Photo by Scott W. Michael

Two physical adaptations have been recognized in zooplankton-feeding fish that may deter predators. There are some zooplanktivores (e.g., damsels in the genera Amblyglyphidodon and Dascyllus) that are deep-bodied — this makes them more difficult to swallow and thus a less-attractive target for fish-eaters. There are other zooplanktivorous species (e.g., fusiliers) that rely on speed to outswim predators back to the cover of the reef.

The zooplankton-feeding labrids would also fall into the last category. Rather than being deep-bodied, these wrasses are torpedo-shaped and built for speed. If a piscivore arrives on the scene, they simply dash back to shelter or away from the threat. This behavioral trait can impact their care in captivity because rather than dash to the cover of the reef, these wrasses sometimes streak upward in the aquarium when startled, which can end up with them flying out of an open tank. This means that some type of cover is essential in order to prevent suicidal aerial displays.

Another behavioral characteristic that zooplankton-feeding wrasses utilize to avoid becoming lunch is to feed in groups. Being in a group not only decreases an individual’s chances of being the target (known as the "dilution effect”), but there is also a phenomenon known as the "confusion effect.” It has been demonstrated that when faced with a group of similarly shaped individuals, a predator may have a difficult time selecting a specific prey item and end up charging the group as a whole and missing out on catching any individual.

red margined fairy wrasse
There is a guild of wrasses that specializes in feeding on minute animals that float about the water column — the male red-margined fairy wrasse (Cirrhilabrus rubromarginatus) is one of these. Photo by Scott W. Michael

Some of the zooplankton-feeding wrasses feed in large groups, such as the bluehead wrasse (Thalassoma bifasciatum). Others are more often found in smaller loose assemblages, such as the redfin fairy wrasse (Cirrhilabrus rubripinnis). Some even form mixed groups with other zooplankton-feeding wrasses (e.g., filamented flasher wrasse, Paracheilinus filamentosus) or even nonrelated fishes (e.g., blunthead wrasse, Thalassoma amblycephalum). While the chances of an individual wrasse being eaten may be diminished by being in a group, these fish regularly fall prey to a number of different fish predators, including lizardfishes, frogfishes, trumpetfishes, scorpionfishes, groupers and jacks.

A group of plankton-feeding wrasses can make a stunning aquarium display. Unfortunately, without predation pressure, the same labrids that readily group in the wild may fight in the confines of the aquarium. In most cases, labrid groups consist of far fewer males than females and juvenile individuals.

In aquarium confines, keeping one male wrasse and several females is most likely to produce a copasetic social unit. Also, space may impact the chances of keeping a group of a particular zooplankton-feeding labrid. The bigger the tank, the more likely subordinate individuals can avoid a male’s bossiness. As mentioned, some of these zooplankton-feeding species will form mixed groups. The same fish communities can be duplicated in captivity; but as with members of the same species, some labrids are more aggressive than others. For example, Thalassoma males can be very aggressive. Also, larger male fairy wrasses may bully other zooplankton-feeders, especially if they are introduced to the tank after the former are well-established.

red-striped fairy wrasse
Like most of the zooplankton-eaters, this red-striped fairy wrasse (Cirrhilabrus roseafascia) will need to be fed a couple of times per day to maintain good health. Photo by Scott W. Michael

Some zooplankton-feeding wrasses, such as Cirrhilabrus, Paracheilinus and Pseudocheilinus species, have a specialized visual system that is thought to facilitate plankton-picking. These fish have a double pupil that may enhance close-up vision so that they can better feed on small prey organisms. All of the zooplankton-feeding wrasses hunt during the day.

Food and Feeding

Zooplankton feeders don’t all eat the same prey types. Some feed on smaller planktors, while others prey on a broader size range of prey items.

Matt Wandell (2010) published a very insightful article on feeding the yellow-striped anthias (Pseudanthias tuka). Long-term keeping of this species had long eluded the majority of marine fishkeepers. Wandell figured out that this species feeds on much smaller prey items than what marine aquarists normally provide to their fish. The anthias eat zooplankton that is less than 2 millimeters in size. While most wrasses have relatively small mouths and small teeth, fortunately for aquarists, most feed on planktors of varying dimensions. This includes many of the food items that are normally fed to captive marine fish. See the various sidebars in this article for information on the specific feeding habits of these wrasses, and the size range of various zooplanktors and aquarium foods.

Yellowfin flasher wrasse

Most of the razorfishes feed on bottom-dwelling invertebrates, but the green razorfish (Xyrichtys splendens) is an oddball that feeds mainly on zooplankton. Photo by Scott W. Michael

Some of the best foods for zooplankton-feeding wrasses are mysid shrimp (which are readily available in a frozen form) and frozen Cyclops (a minute crustacean). Mysid shrimp are very nutritious, and most fish cannot resist eating them. One mysid downside is that they lack some pigments required to keep the colors of certain zooplankton-feeders from becoming dull. Freshwater mysids can also be quite large and may be difficult for smaller wrasses to ingest whole. Some labrids will take these larger mysids in their mouths and bash them against hard substrate until they break into smaller, edible morsels.

Frozen Cyclops is rich in pigments and also high in HUFAs (highly unsaturated fatty acids) and proteins. It also remains suspended in the water column longer than many foods, and smaller zooplanktivores will go nuts over it. There are some frozen preparations that include frozen Cyclops, as well as a number of other items that are relished by fish and corals.

I have found that coral food is especially relished by zooplankton-feeding fish. This food not only includes Cyclops, but it also has bits of shrimp, scallop, oyster, clam, squid, brine shrimp, fish eggs, oyster eggs, Spirulina algae, rotifers and baby brine shrimp. Those items too small for wrasses to eat will be devoured by corals and other invertebrates in a reef aquarium.

Best Reef Wrasses

Because of their tendency to ingest smaller planktonic prey items, the zooplankton-feeding wrasses are the best-suited labrids for the reef aquarium. While few labrids will feed on sessile invertebrates, like your prized soft and stony corals, many species in the family have a particular fondness for crustacean flesh — this may include your cherished fire shrimp or anemone crab. There are also some wrasses that specialize in feeding on fish, such as the cigar wrasse (Cheilio inermis) and ringed wrasses Hologymnosus spp.). While the occa-sional zooplankton-feeder may "go bad” and devour a delicate anemone shrimp or a nano goby, most are not a threat to their ornamental neighbors. The representatives of this guild that are most likely to cause problems are members of the genus Thalassoma. 

Zooplanktivorous Wrasse Diets

So what kinds of zooplankton do these wrasses feed on? Here are some dietary details for some of these labrid species. The zooplankton type is listed in order of its dietary importance.

  • Fairy wrasses (Cirrhilabrus spp.) No specific data available. Reported simply as "zooplankton”
  • Creole wrasse (Clepticus parrae) Calanoid copepods, siphonophores, shrimp larvae, salps (pelagic tunicates), eggs, gastropod larvae
  • Green razorfish (Hemipteronotus splendens) Calanoid copepods, shrimp larvae, fish eggs
  • Flasher wrasses (Paracheilinus spp.) No specific data available — also reported simply as "zooplankton”
  • Sixline wrasse (Pseudocheilinus hexataenia) Harpacticoid copepods, crab megalops, caligoid copepods, shrimp larvae, cyclopoid copepods, mysids
  • Belted ribbon wrasse (Stethojulis balteata) Cyclopoid copepods, calanoid copepods, harpacticoid copepods
  • Redspot false coris (Pseudocoris yamashiroi) Copepods, mysids

There is one disadvantage to keeping zooplankton-feeding wrasses (and other members of this feeding guild for that matter) in the reef aquarium: they need to be fed more frequently than those species that will ingest food items from the live rock (e.g., small benthic crustaceans, algae). If you are one of those reefkeepers that has an aversion to regularly adding food to your reef tank, you will want to steer clear of zooplankton-feeding fish. Planktivorous wrasses will need to be fed at least once or twice a day, while other fish that share their diet, such as anthias, may need to be fed even more frequently. One way to provide a steady influx of live microcrustaceans (copepods, isopods, mysid shrimp, etc.) for your zooplankton-feeders is a productive refugium. A refugium is a separate tank that is free of predators where the aquarist can culture a variety of plankton and other small invertebrates. There are a number of premade models available that can be hung inside or on the outside of the aquarium or that are formed from a portion of a sump. Zooplankton cultures (mysid shrimp, copepods and amphipods) that can be added to the refugium are also available. These small crustaceans can be fed aquarium flake food and plant material and are typically prolific.

The family Labridae includes some of the most stunning fish on the planet, and some of the most attractive labrids feed on zooplankton. I hope this synopsis on plankton-feeding labrids will not only help you keep these in your home aquarium but will also help you better appreciate the natural history of this unique group of wrasses. Happy fish watching!


Scott W. Michael is the author of Reef Sharks and Rays of the World, as well as Reef Fishes: A Guide to Their Identi-fication, Behavior and Captive Care and more. His photos have appeared in publications around the world.


References

Wandell, Matt. 2010. "Boldly Colored Beauties: The Tuka Anthias.” Reefs Magazine, Winter Issue.
Hobson, E.S. and J. Chess. 1978. "Trophics relationships among fishes and plankton in the lagoon at Eniwetak Atoll, Marshall islands.” Fish. Bull. 76:
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