(This article was originally published in Cichlid News Magazine, Apr-99 pp. 32-33, It is reproduced here with the permission of author Ron Coleman and Aquatic promotions).
Thorichthys pasionis males displaying for territory. Photo by Juan Miguel Artigas Azas.
Cichlids fight. Even the tiniest of cichlids will fight. Are cichlids just nasty fish, or is there more to it than that? A closer look at cichlid fighting reveals complex behavior that is well worth watching and understanding.
Although it is common to hear a particular species of cichlid described as "aggressive" or "a more peaceful species," to do so overlooks a lot of interesting biology. Cichlids fight for a reason. Fighting may be over space, over mates, or over food. The intensity of aggression and fighting is much easier to understand if we examine why fish fight rather than just ascribing fighting as a characteristic of a particular species. This is not to say that the outcome of putting an Apistogramma and a convict cichlid in a 5-gal tank is hard to predict, but rather that we might understand why sometimes two fish get along and other times they do not - often with serious consequences for the loser. If we understand fighting, then we can attempt to control it, and our fish will benefit.
Fighting is dangerous. The loser may forfeit scales, fins, or eyes. All too often, in the confines of a small aquarium, the loser may be killed. Fighting is also dangerous for the winner. A lucky strike to the eye by a small opponent could debilitate even the largest fish.
If possible, potential combatants should attempt to evaluate the likely consequences of a fight before the fight begins. If one of the fish stands no hope for victory, it should not enter the fight. We would expect therefore that fish would be astute to gather any pieces of information that might assist them in predicting the outcome.
The issue of animal contests and information transfer before and during them is an active area in animal behavior research. Recently, a growing number of papers have been published analyzing fighting in cichlids, and they are revealing incredibly sophisticated behavior.
A typical fight progresses through a series of increasingly costly stages. At any point one of the combatants may break off the fight, but if the combatants are closely matched, it will proceed through to the end. In any given fight, some of the stages may be omitted or very short in duration.
A fight often starts with displaying. Rivals spread their fins to make the body look as large as possible. If neither is deterred, they may progress to lateral displays, also called tail-beating. The opponents line up side-by-side and push water laterally at each other, attempting to show their strength. If the encounter escalates, the combatants may engage in face-to-face combat. They display flared gills and open mouths, which usually precipitates jaw-locking (also called mouth wrestling and lip-locking) and "carouselling" in which the fish rapidly chase each other in a tight circle, each attempting to bite the other.
Jaw-locking is dangerous because the jaws are essential for so many aspects of a cichlid's life. A dislocated jaw could be a prelude to death. However, jaw-locking is also the ultimate way for two closely-matched fish to determine who wins and who loses. It is so important that in cichlids many species have incorporated jaw-locking as part of courtship: potential mates lock jaws and test each other's fighting ability. A partner that cannot fight is a partner that will not be able to protect the fry adequately.
What determines the outcome of a fight? In many animal contests. body size is a key factor. The larger bodied animal packs more punch in its bites, may have thicker protective parts, more energy reserves, larger jaws, etc. All else equal, a larger animal will usually win a fight. But there are other factors to consider, and these are particularly important and interesting in cichlids.
Motivation is extremely important in cichlid fights. Just watch a pair of breeding cichlids defend their nest or fry against much larger attackers. The parents are highly motivated: they have much more to lose - namely their offspring - than the small amount of food energy that the attacker has to gain. Because of this, parental cichlids are seldom evicted from their broods, and I have witnessed parents effectively turn away predators ten times their body size.
So what evidence do we have that fighting is actually this complex in cichlids? George Barlow and his students at the University of California at Berkeley have conducted many experiments on the Midas cichlid, Amphilophus citrinellum, to show that differences in size are key to determining a winner (e.g., Barlow et al., 1986). A difference of only a few percentage points in weight is enough to predict winners of a staged fight. Similarly, Simon Beeching (1992) showed that oscars can accurately visually assess body size of opponents.
Body size isn't everything. Francis Neat and colleagues at the University of Glasgow examined fighting behavior in Tilapia zilli Neat et al. (1998) showed that if two male T. zilli were placed in a tank, the outcome of the resulting fight was predictable by the relative size of the testes of the males, not by body size. They argue that it is the male's "motivation" - namely his breeding status as indicated by his gonad weight - that is important in determining the outcome. Interestingly, Neat (1998) recently showed that mouth size is a good predictor of testis size; hence T. zilli with disproportionately large mouths for their body size will most likely win fights.
Peter Hurd at the University of Stockholm conducted experiments on the possibility of cooperative signalling between opponents in fish fights. By analyzing videotapes of fights between male Nannacara anomala he showed that particular components of the color display predict the willingness of the fish to engage in certain fighting behavior. For example, displaying a horizontal stripe was coupled with tail-beating while the vertical barring indicated a willingness to initiate jaw-locking.
Sigal Balshine-Earn and Arnon Lotem (1998) of Tel Aviv University took video one step further and conducted some fascinating experiments on Neolamprologus brichardi. One of the difficulties of studying aggression in fishes is that in order to isolate the response of one of the combatants, ideally you need to control the behavior of the other. It is difficult to do this with two live combatants; various alternative approaches, including using rubber dummies or photographic models, have been employed. Balshine-Earn and Lotem applied an exciting new technique to cichlids: they let the fish watch TV! By testing the response of individuals to either live fish or video of live fish, the authors showed that cichlids will respond to video fish - though not as strongly as to live fish - and also, that the fish recognize individuals on the video. For instance, males courted images of their own mates but attacked images of non-mates. The authors point out that cichlids have color vision quite similar to our own, and that the use of video offers exciting opportunities for future experimentation.
There is another cost to fighting that has seldom been addressed: when fish are fighting they might become less vigilant towards predators. Sven Jakobsson and his colleagues at Stockholm University found that when they presented a model predator to Nannacara anomala in various stages of fighting, the fighting activity had a large effect on the fish's ability to react to the predator. Fish actively engaged in mouth wrestling allowed the predator to get much closer before swimming away than did either single fish or fish engaged in tail-beating towards each other. Olle Brick (1998) took the experiment one step further to explain the temporal structure of a fight. When mouth-wrestling, combatants typically break apart every once in a while; Brick showed that the fish are much more vigilant during these times than when they are actively engaged in mouth-wrestling.
Experiments on fighting are difficult to conduct properly and should only be done with a clear purpose and sound methodology. However, it is vital that we attempt to understand exactly why fish fight, because this is an integral part of cichlid behavior and through understanding it, many fewer cichlids will die.
- Balshine-Earn, S., and A. Lotem; 1998; Individual recognition in a cooperatively breeding cichlid: evidence from video playback experiments. Behaviour 135:369-386.
- Barlow, G. W., W. Rogers, and N. Fraley; 1986; "Do midas cichlids win through prowess or daring? It depends"; Behav. Ecol. Sociobiol.; 19:1-8.
- Beeching, S. C.; 1992; "Visual assessment of relative body size in a cichlid fish, the oscar Astronotus ocellatus"; Ethology 90:177-186.
- Neat, F. C.; 1998; "Mouth morphology, testes size and body size in male Tilapia JUL implications for fighting and assessment"; J. Fish Biol. 53:890-892.
- F. A. Huntingford, and M. M. C. Beveridge; 1998; "Fighting and assessment in male cichlid fish: the effects of asymmetries in gonadal state and body size" Anim. Behav. 55:883-891.