Tips for Setting Up A Fish-Only-With-Live-Rock (FOWLR) Aquarium
Veterinary & Aquatic Services Department, Drs. Foster & Smith

This particular FOWLR aquarium includes live rock, artificial corals, and aggressive fish speciesA fish only with live rock (FOWLR) aquarium is a great way to enjoy some of the most colorful and fascinating marine species. FOWLR aquariums contain fish and live rock, but no living corals or invertebrates that fish may eat. Invertebrates that can be part of a FOWLR system include snails, stars, crabs, urchins, and lobsters. A FOWLR setup has an advantage over a fish-only (FO) aquarium in that the live rock in a FOWLR system adds biological filtration. In addition, FOWLR setups are typically less expensive, easier to keep, and less demanding than coral reef aquariums.

Types of FOWLR aquariums

There are two major types of FOWLR aquariums, those with aggressive fish, and those with more peaceful community fish.

FOWLR systems with aggressive fish

Many aggressive fish, though beautiful, will create havoc in a confined reef system with invertebrates and live corals, but in a live rock aquarium, you can enjoy their unique splendor without worry. Common colorful fish species for this type of aquarium include:

Large Angelfish are very colorful and hardy. They have interesting swimming patterns that can add appeal to your aquarium. Many species of angels will also help control algae as they continually graze upon the rocks.

Pufferfish are slower moving fish with beak-like mouths and two fused front teeth. Their jaws are extremely strong, which helps them feed on their favorite food, crustaceans. These fish are very personable, and will learn, in time, to feed directly from their owner's hand.

Because aggressive fish will destroy delicate live corals, you can use some beautiful, lifelike artificial corals in your FOWLR aquarium. They will withstand abuse and do not require the effort and care level of their counterparts.

Tangs, commonly referred to as Surgeonfish or Doctorfish, have small scales and one or more scalpel-like spines on each side of the tail. These spines are used in aggression and for defense. Tangs appreciate hiding places, plenty of room to swim, and a diet of algae and dried seaweed.

Triggerfish are best known for their striking triangular shape and variety of different colors and patterns. They also swim in an unusual fashion, using their dorsal and anal fins. They earn their name from the first dorsal fin, which has a very strong bone that can be locked into place, helping aid these fish in maintaining a position within rockwork.

Wrasse are best known for their bright colors, elongated body, and pointed snout. Some Wrasse will pick parasites and dead tissue from larger fish, including predators. Most Wrasse bury themselves in the sand at night, and also when threatened.

Other aggressive fish that are commonly kept in FOWLR aquariums include predators such as groupers, lionfish, eels, sharks, and rays.

FOWLR systems with peaceful community fish

Gobies and Dartfish are members of the largest family of marine fish. Most are small, with many interesting color variations. Although prawn gobies should be kept in aquariums with shrimp, the other species in this family can do well in a FOWLR system. Be sure to provide a secure top to the aquarium, because these fish like to jump.

Cardinalfish are interesting fish with amazing color patterns and elegant fins, which are often overlooked as wonderful additions to an aquarium. They are often found in groups and prefer live rock with multiple caves. They are mouth brooders, and given the right conditions, it is possible to breed these fish in your tank.

Squirrelfish bring a dash of the color red to an aquarium. Although shy at first, they will soon become bolder in a home aquarium. They have the unusual ability to make clicking and grunting sounds when they interact with other fish.

Chromis are bright, active fish usually found in shoals. They are hardy, long-lived, and often used to cycle a tank. The Blue Green Chromis would make an excellent choice.

FOWLR set-up tips

  • Choose the largest aquarium that is appropriate for its intended location; ideally, a 6-foot setup or larger is recommended.

  • Although live rock supplies good biological filtration, many FOWLR aquariums require an efficient external biological filter due to the size and the quantity of fish. A great choice of filter is a wet/dry, or a sump/refugium.

  • Along with the filtration, an efficient protein skimmer is needed to help control nutrients within the system.

  • Choose a lighting system that provides between 1 to 2 watts of light per gallon. Keep the lighting on the low side of the recommendation if the room is not air-conditioned.

  • Every FOWLR aquarium starts with a sand bed. Sand beds add aesthetic appeal, aid in filtration and pH buffering, provide a habitat for burrowing fish, and help seat and stabilize your live rock.

  • Live rock for this type of aquarium needs to be very porous. Fiji, Lalo, Tonga, and Kaelini are all good choices. Live rock will need to cure with the filtration in operation for about 2 to 4 weeks, until the ammonia and nitrite levels are zero, before you can add fish.

  • Stock your aquarium gradually over a period of a few months, introducing an entire species group at a time, in order from, the least to the most aggressive species. This will allow your fish to become accustomed to the aquarium and will reduce aggression as other fish are added.

With all of the different species available to the hobbyist today, a FOWLR aquarium can prove to be an exciting aquarium that will bring years of enjoyment.

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