column spacer Defenses

Fish defenses

hot buttons for defensive "tasks" for fishes

Defenses of fishes can be categorised into an heirarchical "cascade" beginning with:

1) avoid detection
2) take evasive action if spotted
3) prevent capture
4) prevent being eaten if captured
5) escape

Of these, the last is obviously the most important, but success in any of the others will aid in achieving it. Note that costs and risks to the prey escalate from first to fourth. The fifth and ultimate category, that of escape, can come at any time and won't be considered further here. The first task of any potential prey fish is to avoid detection. Helfman et al. 1997 The diversity of fishes. Blackwell Sci Publ.

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a barracuda taken from a video

"Wow! I turn my head for a moment and the next thing you know there's a you-know-who within arm's reach. Nice face, huh? Barracudas always look a bit mean. But, still, now would be a good time for small fishes to git!" - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Sphyraena barracuda


Fish defenses: take evasive action if spotted: know your predator

  If spotted by a potential predatory fish, the intended prey fish must identify that it is in danger before taking evasive action. The topic of know your predator is considered here, while SWIM NIMBLY & QUICKLY, and FIND A HIDING SPOT are dealt with in a separate section.
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a lizardfish taken from a video

"If a fish is to avoid being eaten it would be good if it could recognise the approach of danger. I wonder if there is a commonality to the features of predatory fish. Maybe a large mouth and forward-facing this lizardfish. Ugly buzzard, huh!?" - Little Cayman 2001

NOTE sand diver Synodus intermedius

  Let's look for some common facial features of a piscivorous fish. Which of these faces suggests that the owner preys on fishes?
photograph of face of a French angelfish
photograph of face of a four-eye butterflyfish
photograph of face of a red snapper
photograph of face of blue tang
No, this is a French angelfish Pomacanthus paru, an eater of sponges and other soft-bodied invertebrates No, this is a foureye butterflyfish Chaetodon capistratus, an eater of coral polyps, worms, and other invertebrates Yes, this is the one. Red snappers Lutjanus campechanus eat fishes and small crustaceans. They are gulping-type carnivores No, this is a blue tang Acanthurus coeruleus. They are primarily herbivorous and feed on seaweeds
  photograph of a red snapper with "predatory features of face outlined"photograph of red snapper with predatory face-outline moved to one sideWell, that should have been easy. The face of a snapper has features in common with other piscivorous fishes, namely, ringed elliptical eyes, down-turned mouth, and a broad face. Karplus & Algam 1981 Z Tierpsych 55:343.

photograph of Nassau grouper Epinephelus striatus
Let's see how this recognition might work. Here's a piscivore, a Nassau grouper, whose behaviour here is one of quiet floating.






A resting Nassau grouper
Epinephelus striatus

photograph of Nassau grouper
photograph of a Nassau grouper with mouth open

If a potential prey fish catches its attention, the grouper turns its head, bringing
the large, down-turned mouth and fleshy lips into view. On attack the mouth
expands rapidly, adding suction to the speed of the strike. The view on the right
might be the prey-fish's last view ever...were it not already swimming for its life.

Before leaving this photograph, consider the facial features
involved in a successful attack. These are listed below


1. large gape: this is facilitated of course by large size of mouth, but also by the small splits on either side that allow for further expansion.

2. large esophagus: this enables large prey to be swallowed whole. There is little or no chewing involved by a grouper before the prey is swallowed.

3. teeth: these are few and small, represented by the white irregular bumps lining the gums along the top and bottom of the mouth. Their function is probably more to prevent a prey from slipping back out once taken into the mouth.

4. pharyngeal gill rakers: these are the large white bumps lining the gill arches. They protect the openings to the gill areas and the delicate gills themselves. In filter-feeding fishes they have much greater relative surface area for sieving out particulate food items, but one wonders in a piscivore whether they may offer any obstruction to the backward movement of the prey in the mouth as it is being swallowed

  Perhaps the grouper was a bit obvious. Let's check out close-ups of other fish faces and try to identify the ones that would be expected to elicit an escape response in the juvenile sergeant-major shown. Photograph of spotted snake-eel courtesy Anne Dupont, Florida.
photograph of the face of a batfish photograph of the face of butterflyfish photograph of the face of a triggerfish
YES, the batfish Ogcocephalus nasutus is a gulper of fishes, and would frighten the little sergeant-major NO, the pointy mouth of a banded butterflyfish Chaetodon striatus has evolved for eating small invertebrate prey NO, although its mouth is toothy, this triggerfish Balistes sp. is specialised for eating shellfish
photograph of the face of a dee-water piscivore
photograph of juvenile sergeant-major
photograph of the face of a barracuda
YES, all this deep-water species needs is a label "piscivore"; the little fish would be wary Sergeant-majors Abudefduf saxatilis are mainly planktivorous and swim over the reef YES, the large mouth and ripping teeth of Sphyraena barracuda are obvious clues as to what it eats
photograph of the face of a parrotfish photograph of the face of a spotted snake-eel Anne Dupont photograph of the face of a moray eel
NO, the jaws of a parrotfish Scarus sp.are specialised for biting and scraping algae from coral rock YES, the spotted snake-eel Ophichtus ophis is a dedicated fish-eater, attacking from camouflaged positions YES, the raggedy dentition of this moray eel Gymnnothorax sp. is a dead giveaway as to its piscivorous habits

NOTE because of the different habitats of this deep-water fish and the sergeant-major it is unlikely that they
would have had contact through their recent evolutionary history but, keep in mind that not only does
the unidentified deep-water species have the "give-away"piscivore facial features described above,
it would also be providing other types of information to the sergeant-major, including chemical
and water-motion cues, and typical predatory behaviour such as eye contact and stalking

  photo/diagram to show dolphin echo-locationBottlenose dolphins Tursiops truncatus eat cephalopods and fishes. Their echo-locatory systems are sensitive not only to direction and distance of prey, but also photo/diagram to show dolphin echo-locationto size. There is evidence that dolphins can discern features relating to the shape of an object from the returning signal, and thus may be able to differentiate between a prey fish and its own predators. Harley et al. 2003 Nature 424 (6949): 667.
hot button for fish defenses hot button for take evasive action if spotted part of fish defenses hot button for prevent capture part of fish defenses hot button for prevent being eaten if captured part of fish defenses