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.


Fish defenses: take evasive action if spotted: swim nimbly & quickly

  If spotted by a potential predatory fish, the intended prey fish must identify that it is in danger before taking evasive action. Topics of swim nimbly & quickly and find a hiding spot are considered here, while the topic of KNOW YOUR PREDATOR is dealt with elsewhere.
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a filefish taken from a video

"When chased by a predator, slower moving fishes, like filefishes, dive to the bottom. Fast-swimming fishes like permits have streamlined bodies and deeply forked tails. Their escape response to predatory attack is lightning swift!" - 2001 Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Aluterus scriptus


photograph of a banded butterslyfish Chaetodon striatus
Coral reefs provide a special chellenge for manouvreing because of the physical complexity of the habitat, in which fishes must feed, mate, and find refuge from predators and storms. Butterflyfishes are acknowledged to be superior at manouvreing through the reef, moreso even than damselfishes and wrasses. Gerstner 1999 Can J Zool 77: 1102.




Deep flattened bodies and good lateral flexibility allow
banded butterflyfishes Chaetodon striatus literally to "turn
on a dime" when they need to race through the reef 0.2X


Also important for manouvreing in paired-fin swimmers such as wrasses, damselfishes, butterflyfishes, and surgeonfishes, is design of pectoral fins. Let's place these groups of fishes into a ranked order of ability to manouvre, as shown in the diagram. Now, study the icons with special attention to general body shape and pectoral-fin design, and see if there is any obvious explanations for the ranking. A list of possibilities is ranking of manouvreability in 4 types of reef fishesprovided below, with explanations. Gerstner 1999 Can J Zool 77: 1102.

NOTE these are fishes that use their pectoral fins (homologous to the arms of humans) for propulsion, rather than their tails


1. body size in relation to manouvreability: fishes that have deeper, laterally flattened bodies like butterflyfishes are more manouvreable than ones with longer, more slender bodies like wrasses, and they tend to live closer to the reef. With their deeper, flattened bodies, butterflyfishes turn corners better than the other species.

2. design of pectoral fins: it is also important for manouvreability that the pectoral fins be inserted more vertically, as can be seen by careful scrutiny of the drawings. Also, as shown in the more agile butterflyfishes and damselfishes the fins are broader and more flexible. Less manouvreable fishes such as surgeonfishes and wrasses have longer, narrower, and stiffer pectoral fins.

3. width of fins relative to length: more manouvreable fishes also have broader pectoral fins relative to their length, expressed as the "aspect ratio" of the fin. The advantage in manouvreability of having prectoral fisn of larger area relative to body size is obvious.

Perhaps the ultimate in swimming fast/nimbly to escape predators is found in flyingfishes. drawing of a flying fish swimming
When swimming slowly or at when at rest the pectoral
fins are held alongside the body and the pelvic fins are
close to the body.In Caribbean flyingfishes Hirundichthys
only the pectoral fins are used for gliding

Takeoff acceleration is attained by rapid beating of the extra-large tail fiin (50-70 beats per second), and this continues on the sea surface until the fish becomes completely airborne. At this time the pectoral fins are opened and spread to the sides, and the pelvic fins are extended downwards for stability. Davenport 1990 J Mar Biol Ass UK 70: 31.

Because there is no propulsion, fyingfishes do not actually "fly"
(among animals only birds, bats, and insects have this capability).
However, the shape and extension of the pectoral fins provide
sufficient aerodynamic lift for the fish to glide above the sea surface:
distance: 50-400m, velocity: to 90km per h, and height: 3-8m

drawing of a flyingfish in flight

Take evasive action if spotted: find a hiding spot

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a southern stingray burrowing in the sand taken from a video

"One strategy of evading a predator is to hide in the sand, just like this southern stingray is doing when the diver approaches." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Dasyatis americana


photograph of a yellow stingray
Many fishes hide in sand when confronted with perceived danger, and some remain buried in sand during all or most of the day. This enables them to avoid their own predators and/or permit ambush-attacks on their prey.

photograph of a spotted snake eel Ophichtus ophis courtesy Anne Dupont, Florida
Yellow stingray Urolophus jamaicensis emerging from its sandy hiding spot 0.25X


A night-hunting spotted snake
eel Ophichtus ophis. Photo
courtesy Anne Dupont, FL 1X

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a razorfish about to enter the sand, taken from a video

"I guess if you've got a head like a brick you can just dive right into the sand when danger threatens. Like a razorfish. Apparently, they go 10 to 20cm into the sand." - Turneffe Island, Belize.

NOTE Hemipteronotus martinicensis


photograph of rosy razorfish Hemipteronotus martinicensis
Rosy razorfishes Hemipteronotus martinicensis may seem to dive into the sand anywhere, but they actually have preferred locations where the sand is softer.  Their heads are also sharply shaped to enable more easy entry.  Males are territorial, possess harems, and will defend against intruders. 
Shen 1985 Archiv Ribicon Found P111.



A fast-swimming rosy razorfish
Hemipteronotus martinicensis

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a jawfish near its burrow

"Oh, here's a nice married couple...they're jawfishes, sharing the protective benefits of a burrow. Over here are some garden eels. They're always so timid, and it's frustrating to try to get close to them." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Opistognathus aurifrons

Permanent burrows are used by a few reef fishes as a protective hideaway from their predators. photographs of jawfish Opistognathus aurifrons and its burrow
photographs of fishes that live in burrows

scenario where piscivorous fishes have chased a jawfish Opistognathus aurifrons into its burrow
A jawfish Opistognathus aurifrons uses its burrow primarily for protection from piscivorous (fish-eating) fishes.  In the Bahamas an individual will duck into its burrow in response to approach by at least 15 piscivorous species and, for 3 of these (Nassau grouper Epinephelus striatus, yellowtail snapper Ocyurus chrysurus, and white margate Haemulon album), may even cover the opening with a stone.  In general, when danger appears a jawfish will settle tailfirst into the burrow but, in an emergency, will dive in headfirst.  Small fishes such as wrasses Halichoeres spp. may be chased away by the burrow owner with jaws gaping and/or with sand spewing from its mouth. Colin 1971 Copeia (3): 469.

NOTE  this is a routine behaviour for jawfishes who, after a day spent feeding on zooplankters at the burrow entrance, will retire within and close off the opening with a stone


photograph of yellowhead jawfish Opistognathuys aurifrons hovering over burrow entrance Construction of burrows by yellowhead jawfishes Opistognathus aurifrons takes place during daytime and requires about 8h.  Major steps are removal of sand to create a pit, collection of rocks and coral bits, and “masonry” (see drawings below).  Burrow depth is about 15cm and the fish takes care not to exceed this by much.  This is likely because a 1cm increase in depth at 20cm requires that 4 times more material must be removed than at 10cm owing to sand subsidence.  The author suggests that mucus cementation is likely not involved in the construction, but look at the preceding photograph of a burrow entrance.  If not destroyed by weather events or other calamitous events, an individual may occupy the same burrow for its entire life.  Colin 1973 Copeia (1): 84.

NOTE  3 types of burrows are actually constructed: under-rock, open chamber, and hole-in-rock.  The second of these is described here

Yellowhead jawfish Opistognathus aurifrons hovers
over its burrow opening on a Bahamian reef. Burrow
construction involves considerable shifting of sand
and other materials, done by fanning with fins and
carrying in the mouth

Steps in construction of the burrow:

drawing 1 in a series of 4 showing burrow construction by a yellowhead jawfish Opistognathus aurifrons drawing 1 in a series of 4 showing burrow construction by a yellowhead jawfish Opistognathus aurifrons drawing 1 in a series of 4 showing burrow construction by a yellowhead jawfish Opistognathus aurifrons drawing 1 in a series of 4 showing burrow construction by a yellowhead jawfish Opistognathus aurifrons
Hours 0-2: sand is removed by fanning of body and anal fin to form burrow opening Hours 2-5: rocks and rubble collected from area surrounding burrow Hours 3-6: rocks and rubble positioned at mouth of burrow Hours 5-8: adjustment of materials to make the opening level with surrounding surface

photographs of a colony of garden eels Heteroconger longissimus and a burrow entranceGarden eels Heteroconger longissimus (Nistactichthys halis) live in colonies that undulate as the fishes feed and move up-and-down in their burrows.  An individual rarely leaves its burrow, but when it does it re-enters tail-first.  Unlike the jawfishes noted above, garden eels dig their burrows with their tails rather than jaws and fins.  They feed from their burrows on small zooplankters, such as copepods, invertebrate eggs and larvae that pass by in the current.  Most of their vision is therefore close-up, and over evolutionary time their eyes have shifted to a more anterior binocular location.  Prey are mostly sucked in by rapid expansion of the jaws and swallowed whole.  Burrow morphology is not described by these authors but, based upon the image seen here, it is probably lined with mucus .  Schepper et al. 2007 J Morph 268: 343.

Garden eels Heteroconger longissimus in Bermuda occur as male/female pairs in closely adjacent burrows throughout most of the year. Spacing between paired burrows (17cm) in Bermudan colonies is about 5-fold less than spacing between burrow pairs (85cm).  Pairing is not evident in this photograph.  Tyler & Luckhurst 1994 Northeast Gulf Sci 13 (2): 89.

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

"Who's in here, do you think? Well, the crevice is filled with cardinalfish, but it's too dark to see them properly. Ahh!'s somebody we can see. It's a flamefish, waiting for nightfall." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Apogon maculatus


photograph of blackbar soldierfishes Myripristis jacobus
Night-hunting squirrelfishes, soldierfishes, and cardinalfishes seek safety beneath rock overhangs during the day. Good crevices must be large enough for water circulation, but small enough to keep out predators.






Blackbar soldierfishes Myripristis jacobus 0.3X



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