VII. "Reef Safe” - A Word of Caution
This article discusses Compatibility, Temperament, Dietary Concerns.
When considering additions of the scaled variety, we will often look at our options based on aesthetic value. A beautiful specimen showcased in a reef tank is the highlight of many hobbyist tanks, but, these additions are not without their own research and understanding into whether it is an appropriate choice for your tank. The first challenge with many fish is size, many fish will appear small due to the age when observed at your local fish store, it is much rarer to see full-grown specimens of the same species as their age and maturity would mean a shorter lifespan after purchase. Seeing a school of one inch Paracanthurus hepatus babies can easily tempt a beginner aquarist to consider them, not realizing that once adults these fish will be over fifteen inches long and require a large area to swim around in to remain healthy. Alternatively, the diminutive Tilefish stays small but due to diet is also considered a bad fit for a reef tank. As a whole, if you are capable of rehoming fish as they grow too large, size is not as big of a determining factor as to whether or not the fish is considered "reef safe".
Compatibility
"Reef Safe" is a matter of compatibility, fish labeled as reef safe often boast a level of compatibility with coral and invertebrates that rarely results in a loss. Reef safe fish, as a result, is often the most common option available to the reef aquarist and they are usually hyped up and advertised as great fish for a reef tank. This level of accessible and easy to understand marketing comes with a hitch. In order to best understand this caveated drawback, it is first necessary to define the level of compatibility we expect. When purchasing a fish we commonly want something bright and colorful as found on the reef, additionally, we overlook that reef fish do not leave the reef to find food, meaning that whatever they eat is found on the reef. This should sufficiently outline the paradox of "reef safe" fish, boldly I will state that since all fish that live on a reef fit into the food chain of said reef, there is no such thing as a truly "Reef Safe" fish, there can only be fish that do not eat a specifically desired inhabitant.
This level of compatibility adds variables that are not easily addressed in a "one and done" style article and thus specific information about each specific fish should be obtained before making any additions to your fish population. Reef safe in our definition then takes on a slightly more in-depth meaning than a simple term for marketing. Reef safe decision combines aspects of our tank; size, lighting and aquascape and aspects of the fish to determine whether something is compatible with our tank specifically. When reviewing a fish for compatibility its maximum length, temperament, and dietary needs should also be considered in-depth before purchasing.
Temperament
While it can be daunting to consider so many factors before purchasing a new fish there is no better reason to consider this information than avoiding a potential loss. It can be hard to see because they are usually so small, brightly colored and begging of a "cute" description, but many fish are supremely territorial and some are downright nasty with regard to aggression. Starting a tank with five damselfish may seem great as they are inexpensive and relatively hardy, however, when you consider their territorial temperament you will realize that this is setting yourself up for failure. Damselfish group into large schools for protection when swimming along the reef, in large groups their territorial disputes are easily dispersed through the school so no one fish takes too much bullying from the others. In your tank, the limited number of conspecifics and space means that the smallest and least aggressive fish will be a constant target for the others in its grouping. This will lead to eventual sickness and loss of the weaker damsels eventually leaving only the strongest most aggressive fish from the school.
When the day comes to add to this rowdy bunch of rascals, you may watch on in horror as the new fish you add is swarmed and bullied from the moment it enters the tank, over the coming weeks the fish will struggle to find food as it is bullied away at feeding time, it will struggle to find peace as it is constantly sought out and chased as it is seen as an invader to the damsels. Eventually, the fish will develop stress-related health defects and may inevitably die from the stress. We do best to consider this scenario carefully when making selections. Always use the aggression level of your tank to dictate the pugnacity required in a new addition to "make ranks" and compete in your tank. Often the best solution is to instead start with peaceful more diminutive fish, allow them to settle in and adapt to each others company and slowly increase the level of aggression of new fish being added. Once more peaceful fish have established "homes" and territory they will more easily find relief from aggression and in some cases are become more pugnacious, defending their territory against would-be attackers.
Dietary Needs
With basic requirements like size and temperament considered the last and most important factor in selecting a fish is their dietary needs. Many fish eat coral or other invertebrates like snails and hermit crabs or are strictly piscivorial, requiring the addition of feeder fish. Often these dietary concerns are easily addressed, you may simply adapt your feeding or livestock choices to accommodate the new addition. Some fish, however, will require more consideration of factors beyond our control.
Thousands of aquarists covet the Mandarin fish as one of the most exquisite "reef safe" fish available, it's comparatively low price tag combined with spectacular beauty make it easy to understand this opinion. However, the small Indonesian fish survives the daily struggle of the reef by hovering through cracks and crevices where the crash of the waves is slowed to a steady stream of current. As a result of this, they have evolved to have a very specialized swimbladder and they do not make strong swimmers(this contradicts a corals desire for strong randomized flow patterns). Additionally, they spend every waking hour meticulously scanning the rocks for microcrustaceans like amphipods and copepods, their primary food source. When a natural food source is very specific the predator, as in the example of the Mandarin, lacks complex mouth parts designed for omnivorous grazing. This means Mandarin often starve in a tank as other fish are also consuming the microcrustaceans and it is not likely to adapt to any offered food source.
The demand for a Mandarin that is easier to care for has sparked an aquaculture effort to raise mandarin that eats commonly available pellet foods, however, the success rate has been limited and the availability of these captives bred fish remains scarce. Instead, we should as hobbyist focus on keeping fish that have more diverse diets so that we do not rely solely on the living organisms in our tank. Over time the microcrustacean population ( a part of our reef) may become overhunted, reducing their population, this leads to more detritus not being consumed and more waste polluting our tanks, at this point we can see the irony in labeling something from the reef as "reef safe".
A mandarin fish is completely safe for all coral as it is incapable of nipping at them, completely safe for all tankmates as it will never start a fight and spends all of its time eating, and completely safe for all your snails, hermit crabs and other critters, it is also, a merciless copepod destroyer, a leveler of amphipod empires and the harbinger of terror for all things tiny. I joke but the overarching effect of a decimated pod population is an increase in waste as the small particles of food and waste that they survive off will be unaddressed and left to degrade calling for more water changes to address the accumulating waste. In a large system this may be avoidable by periodically dosing your tank with pods, but in a smaller tank the density of pod life required is not sustainable and the fish will eventually starve once the natural food source is depleted. For this reason I have a hard time recommending this as a "reef safe" fish, yes it has all the earmarks of compatibility but it also has a pretty significant care requirement that if meant may mean poor conditions for coral as they do not tend to tolerate low flow or barren tanks that have no microfauna to assist in the stability of the ecosystem.
Once we have considered all aspect of a fish before purchasing it, we should quarantine the specimens before adding them to our display tank. Careful observance of the above factors does not alone guarantee success as even if you meet the space, compatibility and dietary requirements of a fish, parasites, bacteria or fungus can cause additional problems. With careful consideration combined with proper quarantine protocol, however, we do approach a measurable success rate worth bragging about. When a tank is allowed to age for years and the inhabitants can grow before your eyes there is an additional level of appreciation for the results than when you arbitrarily purchase fish and dump them into your tank. Usually, with the latter approach, you will only succeed in bringing more frustration and never exceed the plateau created by hasty start-up mistakes.