Firstly, let me just pass on my sincerest thanks to both Randy Donowitz and Jonathan Hale for allowing me the privilege of writing for such an esteemed source. I’m sure many of you will be sitting there saying, “Simon who?” So to fill in the gaps, I’m not a scientist and I’ve never claimed to be. I don’t “work” within the reef aquarium trade as such, although many treat me as though I do. Beyond doing the odd bit of consultancy, a few presentations, dabbling in both captive and wild reef photography, and writing for various publications over the years, I am just your average everyday reef keeper. Okay, so maybe I’m a little bit more vocal and active than some, but make no bones about it, I’m just as mad about reefs and reef tanks as the next guy. I have been since I was a child, and at nearly 40, I will probably be so until the day I die. With all that out of the way I’ll move onto the real subject of this article, which is a look at our piscean friends, and to try and break down some of the many curve balls they frequently throw at us in a seemingly effortless drive to make the most patient of keepers go nuts with frustration.

If someone had asked me way back when I first started keeping marine species, “what is more difficult to keep, fish or corals?” no doubt I would have started shaking at the thought of coral husbandry and come out in a cold sweat. Twenty plus years later I’m a little bit the wiser, and I now have no reservations with saying that if it weren’t for the fish, reef keeping would be a doddle. You see, corals – yes, even SPS – are for all intents and purposes pretty easy as long as you stick to a few simple rules: good stable water quality, a bit of food, the right flow, the right light, and enough space to grow. As soon as you put fish in though, it gets all complicated. You now have to question every move you make – who will play nicely with who, who will take a fancy to your prized collection of Blastomussa when there are far more tasty ‘and less expensive’ morsels to devour, and who will turn into a psychopathic lunatic. Fish, in many cases, can be either angelic patrons of a reef tank or the devil incarnate. Just ask anyone with a Pseudochromis steenii and you will see what I mean.

No doubt some of you will have read the paragraph above with either a knowing smile, nod of acknowledgment, or a bit of a giggle. But herein lies the root of most of our problems. You see, all too often we credit our fishy friends with character traits derived from human experiences and emotions that simply do not exist in their world. We do it in an effort to come to some level of understanding and connection with our charges, so that we can quantify their habits and behaviour as though we were trying to understand the various squeaks, squawks and giggles of a new born baby. All too often we group certain fish under the banner of ‘problem’ species, such as many of the dottybacks, most of the Acanthurus family, many of the larger angels and quite a few of the damsels. Maybe what we should be asking ourselves is whether these fish are not so much the “bad boys” we commonly accuse them of being, but rather examples of species that are more prone to the psychological and physical stresses and strains we force them to endure in captivity.

The first rule when looking at piscean behaviour is to leave our emotions behind as extremely complex social animals, and come to terms with the fact that behavioural characteristics in fish start and end under the influence of just a few basic biological needs. They all need to feed. They all need to defend themselves against predation, and they all need to reproduce. Each and every species of fish derives its characteristic behaviour from these three key biological needs. When we look at any species of fish we can categorise its dominant behavioural characteristics and put it under one or more of these headings as a causal factor.

As an example, why do anthias such as Pseudanthias squammipinis and many other species shoal? Well they certainly don’t do it just because they enjoy each others company. They do it because, first and foremost, in the absence of any other defenses there is protection within a group that divides the likelihood of a predator devouring them by a factor equal to the total number of individuals within that group. Instead of each fish having a chance of survival of 50/50 as a solitary individual, they can live a life at 100/1 or 50/1 or any number of variants in between dependent on the size of the group. They don’t actively choose to live like this. Instead, they have this trait genetically built into them before they even hatch as fry, which is why solitary individuals housed in captivity frequently pine away. The fish doesn’t understand what’s wrong with it in terms of feeling happy or sad, all it knows is that it is exposed, and under threat of predation all the time which leads to stress and a shift in behaviour away from the norm. The second reason is reproduction. If a female is lost to a predator at a crucial time, then there is no issue – especially if there are 100 more to choose from immediately at hand.

Equally we could look at species such as grazing blennies, which are renowned on reefs and in some tanks for vigorously defending a given area against nearly all intruders. In such cases, the need for self preservation has commonly been suppressed to a degree (hence the apparent aggression) by the need to protect a food source which may be a particularly nice patch of turf algae that forms the basis of its ongoing food supply. In such cases it will not be uncommon to see these fish not only take on individuals of the same or similar species, but we may in fact see them take on species that are unrelated and of a significantly larger physical size. A good example of this that is that quite commonly bristletooth tangs and algae blennies will not tolerate each other within the same area.

The above two scenarios are by and large ‘set’ ongoing patterns of behaviour, that are seen in various families of reef dwelling fish.

Transitional changes in behaviour are more commonly brought about by a shift from juvenile to adult breeding status within a group or as individuals. Many species of the surgeonfish, butterflyfish and angelfish families are well known for their more sociable behaviour as juveniles in aquariums, which is why we commonly hear that such and such reef keeper has successfully mixed certain species that would otherwise not normally have cohabited together. In such cases we are commonly tempted to try and break the rules ourselves in an effort to emulate that success whilst being unaware of the exact criteria that led to that individual’s success in the first place. We should always remember that nature has in most cases deeply ingrained behavioural characteristics into nearly all species at a genetic level, and that sexual maturity will herald very different social characteristics to the more sedate and easygoing traits of the juvenile form. For example, many Pomacanthids (i.e. Emperor, Blue ring, and Koran angels) exhibit typically shy and retiring natures as juveniles. They start life as passive social cleaners with the universally recognised blue and white cryptic markings in an effort to avoid unwanted predator attention and aggression from adults of the same species. Switching completely through maturity to the brightly coloured and conspicuous adult stage, they will commonly become the dominant and most aggressive fish in an area. The thing to remember here is that this change in social behaviour isn’t a considered action on the part of the fish, it is ingrained at a genetic level. In the home reef, this change is, in the vast majority of cases, followed through. The absence of a breeding partner in captivity won’t diminish these characteristics completely. As far as the fish is concerned, the fact that there isn’t a mate at hand doesn’t mean there won’t be one swimming by soon. Much the same as a sub adult sets itself up with a territory in the wild, we should only expect that during the transition from juvenile to adulthood, the fish we house in captivity will see its surroundings increasingly as its patch, and it will want that patch to be of a suitable standard and size to entice a mate to live there, usually at the expense of its tank mates. In such cases it is wise to foresee such events by limiting the number of fish present to a degree where the most dominant fish has the space to express itself without the need to become overly aggressive. Keeping other tank mates to much smaller less threatening species may well be the key, i.e. keeping the angelfish as the main show fish, and keeping all other species to small non invasive species such as blennies, gobies, dottybacks or the like. In nature these non invasive species will commonly be allowed to venture through such territories unhindered, as they are not seen as a threat to either the food supply or status of the territory holder, unlike similar or physically matched species such as tangs or butterflies that are.

In certain cases it seems that some fish never actually get the chance to become dominant territory holders in closed systems. This is commonly the case in heavily stocked aquariums where there is an over abundance of competitors, to the degree that sexual maturity and breeding behaviour is inhibited to non existent levels. Many would argue that this shouldn’t be seen as a mark of good or clever inter-species mixing though. Rather, it is an extension of the characteristics many species show when in the heavily crowded confines of the dealers’ tanks. In such cases the fish is so heavily tied up with the day to day quest of finding enough food to survive within a group of competitors that this basic biological requirement has by and large overruled all other priorities including territory formation and breeding drive.

The other aspect to the lack of aggression commonly found in dealers tanks which can give a false impression of an individual’s character is the lack of geographic markers which are essential for any fish to form the basis of a territory. Adult and sub-adult fish that are introduced into a new aquarium rarely exhibit any form of territoriality straight from day one. It usually builds over a short period of a few days to weeks. If you have ever noticed the skilled and blindingly quick dash a startled fish can make through a host of corals into its favourite crevice or cave without hardly ever scratching itself, then you will also have no doubt that the route it took to get there is a well traveled and familiar one. This is a key factor of building a territory. Besides its suitability for breeding, enticing a mate, and as a source for feeding, that area must also provide sufficient bolt holes or cover for the quick avoidance of a predator. The terrain must be learned and memorised so efficiently that the flight response to that location becomes automatic. In the absence of key geographic markers that define that territory, the fish has no area to set as its own; hence the common lack of aggression encountered in the crowded-but-bare dealers tank. If a rock is placed in the middle of that tank, you will see a rapid change in behaviour of the fish present. This can be frequently witnessed when large groups of damsels or dottybacks such as the P. fridmanii or Arabian dottyback P. aldabraensis are housed in the same tank prior to sale.

This trait helps us in two ways. Firstly, it sets a trend that we can use to our advantage when keeping similar or normally mildly incompatible species together. By splitting up our rock structures into several separate areas, we can provide different territories within the same volume and each fish will adopt one or the other structure as its own. It will use the other structure as a boundary marker and stand off zone, similar to what commonly happens in the wild between neighbouring individuals of the same species. Secondly, it allows us to rectify existing issues in a set up where one fish has taken control of the whole rock structure as its own to the detriment of other tank mates. In these cases, a strip down of the rockwork and re-arrangement into two or more separate areas not only disrupts the geographical markers of the existing territory holder who has to start all over again, it will also make way for the less dominant party to settle into an area of its own where it will feel more secure, less exposed, and more importantly, less harassed. This manoeuvring of the geographical markers also heralds another benefit that is commonly lacking in many reef wall type setups. Creating a series of structures breaks up the line of sight of each fish, giving them periods as they move around where they can’t see each other. A fish that can’t be seen isn’t treated as a threat, whereas a fish that is constantly in anothers face is a prime candidate for harassment if it is seen as a competitor. With careful planning and consideration for territorial needs, it is quite possible to mix several differing families within the same volume, to the degree that we can have overlapping territories of unrelated or non competitive species sharing the same physical space.

When we talk of problematic species such as the Pyjama tang (A. lineatus) or the Powder Blue tang (A. leucosternon), we commonly hear stories of how it started out fine, but just turned “nasty” as it got bigger. What we have to question here is why it became more aggressive towards other tank mates. Nastiness is a human trait derived of the wish to inflict harm on others out of selfishness. Fish aren’t selfish, nor do they wish harm on others. They simply respond to their own biological needs and follow through with a course of action that fulfills those needs be it to secure a territory. In fact, it isn’t even in the fish’s interests to fight as such, because the loss of an eye to even the most outmatched opponent will quite commonly result in death by predation at a later stage out on the reef. Early symptoms of increasing tension or shifts towards setting a territory are fin flashing to competitors, glancing swerves in the interests of scaring the opponent, or even rapid changes in pigmentation as a means of displaying agitation. It is at these times we need to start considering just how we are going to deal with these issues before the fish with no other course of action available to it starts getting physically violent towards its competitors in an effort to rid the area of them.

Diet and food supply are probably the biggest factors in overall behaviour. Without sufficient food, a fish will fail to reach breeding maturity or potential, and the survival instinct will become suppressed. This results in either a fish becoming extremely aggressive to all around it at the expense of its own safety in an effort to protect or harvest what little food it does get, or withdrawn to the degree that it starves itself in the face of more aggressive tank mates. On the reef, fish spend approximately 95% of their waking time in pursuit of food. The remainder is spent either defending that supply in the case of grazing territorial species, or breeding. In the average home reef, that ratio is greatly skewed to a fraction of that time spent feeding and the remainder just being taken up with waiting to be fed. To be fair, in recent years, the trend for heavier feeding and advancements in filtration methodology have meant that we now see on average much more mentally stable and well fed fish than we did many years ago when the drive to keep water quality high meant that minimal feeding was deemed necessary and pretty much the norm. Though even today, we have a tendency to feed in one or two sessions over the course of the lit period, rather than feeding in a more natural manner that keeps the fish’s digestive system topped up throughout the day. Feeding in small amounts throughout the day usually heralds both a more stable psychological nature and a healthier, better coloured specimen. Obviously an auto feeder can help tremendously in such cases, and should be on the Christmas shopping list of any serious fish keeper, especially those housing active species with high metabolic rates such as anthias, chromis, damsels and many of the smaller wrasses which require an almost persistent but small volume stream of fine foods if they are to really thrive as nature intended. In nearly all cases, fish that are deprived of food for long periods between feedings become mentally unstable with regards to their tank mates. With little to do but cruise around and scavenge any measly morsels left over, they will frequently show a heightened sense of aggression towards other tank mates in an effort to protect what they deem as their feeding area against trespassers or competitors.

With recent advancements in the field of nutrient control and with the advent of Ultra Low Nutrient Systems (ULNS), we have also seen a significant drop in the amount of free algal growth encountered in a lot of systems, which whilst good for the corals, sometimes isn’t so good for grazing species that are used to living off algal films or turf patches in the wild such as the algae blenny and many of the tang species. In such cases it becomes even more important to offer suitable substitutes for them to graze on throughout the day. This can be in the form of algae sheets placed in various clips around the aquarium, interspersed with pellet or flake feeds by way of an auto feeder. In the case of multiple tangs, then the use of several clips can help prevent mounting tension as the fish can split apart to feed peacefully in different locations. Bristletooth tangs need foods derived from small crustaceans in addition to algae sheets as these fish also derive a good proportion of their nutrient intake by way of the micro fauna and detritus films eaten as a consequence of grazing algal patches in the wild. But in here lies a double edged sword. Ultimately the next and logical stage for a well fed fish is breeding, and even in the absence of a mate many species will hover on the border of breeding readiness if fed well enough. This can lead to a shift in character possibly towards aggression as a means of securing the tank or a section of it as a breeding or mating area. So again, some forward planning prior to purchase is a good idea if we want to avoid problematic issues later with sexually mature fish.

One thing I like to do occasionally though is speculate possible scenarios that could answer some of our most perplexing issues. And whilst many would consider ‘speculation’ to be the route of all evil and misunderstanding within our hobby, I tend to believe that it can ‘on occasions when born of some educated guesswork’ form the beginnings of a good idea, or start the ball rolling in a direction that offers some forward thinking into areas that may not have been considered previously. And as we all know, If we aren’t willing to open ourselves up to new ideas, then how are we to progress? So with that in mind I will close with a hypothetical suggestion, on a scenario that frequently puzzles us as reef keepers

One of the most perplexing scenarios commonly encountered with many of the larger species of angel fish and certain other families is the fact that they live peacefully in the presence of many species of LPS corals and clams during the juvenile phase of growth, only to turn into LPS and clam ravaging monsters as soon as they cross over into adulthood. This is by and large a mystery within the hobby. It is evident that as adults on the reef, large angels are not the LPS gobbling monsters they appear to become in captivity, preferring a diet of algae, sponges, tunicates and other sedentary organisms rather than suffering the relatively unsavoury taste of a stinging coral. So why the shift in diet in captivity? Well, it is pretty clear that many keepers simply do not include these essential food types in the diet of the fish during its time in captivity as a juvenile, frequently forcing the fish to live on a diet alien to its natural digestive system. Whilst juvenile, this may not be such an issue as there are only nominal demands for nutrient uptake in the interests of basic growth and biological function. Upon switching to the sexually mature adult phase, it may be the case that the biological needs of the fish shift slightly, and a priority for certain types of food stuffs becomes an over-riding urge for the fish in question.

Let’s just hypothesise for a moment. It is already accepted that in many cases when fish suddenly switches to devouring our prized corals, that we are dealing with adult or sub-adult captive specimens. Most adult or sexually mature fish are constantly ready to breed from the moment they reach maturity. So it may be acceptable to assume that once hitting sexual maturity, the dietary urges of some fish may shift somewhat away from the rather fixed and meager diet we commonly subject them to, and that unconscious urges are brought into play by hormonal changes. The net result is that it is driven to try differing food stuffs with the aim of satisfying some biological need for a more varied diet, or to make up for something that is lacking in its current feeding regime. Remember here though a key factor: an adult fish feeds itself up in preparation for breeding. Beyond its normal intake of food as a means for survival, its secondary interest is in generating enough surplus energy to allow it to breed as often possible.

How does this help us? Well lets just suppose that we are caught up in one of these scenarios, where we have had a fish in captivity for some time, it has reached adulthood and it starts to take an interest in corals that it has up until that stage largely ignored. We have to consider two factors. One is that fish are habitual; once they get into a certain circle of constant behaviour, they will commonly continue it until the cause of that behaviour is removed. In this instance, we have both the corals presence as a food source, and the fish’s need for it as nutrition. Simply removing the coral won’t get rid of the urge, and we won’t know what it is exactly that the fish was getting from that coral in terms of nutrition, so we may consider a two-fold attack on the situation. First, removal of the coral to an alternate system to break the chain of behaviour. Second, expand the fish’s normal diet by way of researching natural food sources that the fish would consume in the wild, but which we may be depriving it of in captivity, such as sponge based foods, mollusk meat, or a host of other desirable constituents. Once we have spent some time trying differing food types and expanding on the previous ranges that we were offering, we can then re-introduce the coral to see whether we have broken that chain of behaviour and filled in the missing gap in nutrition that was possibly being encountered. We commonly resign ourselves to accepting certain character traits in our fish, and put such instances down to the fact that maybe the fish simply likes the taste of that coral. But what if that character trait is born of more subtle and uncontrollable urges that we can influence by way of dietary research and adjustment? In which case, do we really need to just sit back and accept that behaviour as the norm, or just a risk of housing such species in a mixed reef environment?

If nothing else, I hope this article has triggered some degree of greater appreciation and understanding of what drives the behaviour of our piscean charges in captivity, compared to what happens in the wild. If we can get a better handle on how to manoeuvre that behaviour, we have a better hope of housing species that would normally not cohabit on the reef.

Many thanks for reading,

Simon Garratt.
All photos by Simon Garatt.