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This is the largest order of fish with a high level of diversity and confusing taxonomy (see Helfman et al. 2009; Nelson et al. 2016). These are “typical fish”. Species that may be commonly seen in display aquariums and aquaculture include the following:

 Acanthuridae: tangs, doctorfish, surgeonfish. These have one or more scalpel‐sharp spines bilaterally on the tail that can present a significant hazard during restraint.

 Anabantidae: gouramis, bettas. This group uses a suprabranchial organ as the primary breathing apparatus; they need an air space to survive. Males create bubble nests as part of their reproductive strategy. The lips have horny teeth used for scraping algae.

 Blenniidae: blennies, cleaner wrasse. These animals often bury. They create water flow over the gills while buried using branchiostegal membranes that form small gill openings and function as a ventral pump, rather than the lateral opercular pumping of other fish. They also have finger‐like projections that keep sand out of the gills.

 Carangidae: jacks, dolphinfish, cobia, remoras, lookdowns. Remoras lack a swim bladder and have a unique disc on their head for adhering onto other animals. In some jacks, the swim bladder extends to the end of the peduncle.

 Chaetodontidae: marine butterflyfish. These have a spine at the angle of the preopercle. The gastrointestinal tract is coiled many times. The swim bladder has two cranially directed processes.

 Cichlidae: cichlids, freshwater angelfish, discus, tilapia. Tilapia are important foodfish (Oreochromis spp.). These fish have a single nare on either side of the face, unlike the paired, rostral nares of most species. These fish have unique and highly organized breeding activities and may be mouthbrooders or substrate brooders. Female discus secrete a milk‐like substance from the skin to feed their fry.

 Pomacanthidae: marine angelfish. These have a spine at the angle of the preopercle that can be a hazard during handling (Figure A1.21).

 Scorpaeniformes: gurnards, scorpionfish, stonefish, rockfish, lionfish, sculpins. Most lack scales, but scales are ctenoid when present. The swim bladder is absent in some genera (Plectrogenium and Sebastolobus spp.). The gurnards (Triglidae) have huge pectoral fins which expand as they walk along the substrate using their pelvic fins. Most have spines projecting from the head including a caudally directed spine derived from a bone below the eye. In scorpionfish (Scorpaenidae, which includes the lionfish Pterois spp.) and stonefish (Synanceiidae), there are venomous spines along their dorsal, anal, and pelvic fins. Lumpfish (Cyclopteridae) are round with bony tubercles arranged in rows around their body and a sucking disc made up of modified pelvic fins. Most show internal fertilization and some show live births (e.g. Sebastes spp.) (Helfman et al. 2009; Nelson et al. 2016).

Figure A1.21 Preopercular spine on a marine angelfish.

Source: Image courtesy of Catherine Hadfield, National Aquarium.