Stocking Techniques for Fish...

There are a few time-tested techniques to help a new collection of fishes coexist and to prevent fatal aggression. Add more hiding places and reeflike décor - caves, nooks, crannies, and promontories or rocky walls - places where a fish can stake out a territory and disappear from time to time. You should also establish and follow a daily timetable for lighting and feeding. These routines are not very often written about, but environmental cues are crucial in the lives of coral reef organisms that follow highly ordered daily patterns dictated by the sun, moon, and the predictable availability of foods. Disrupting their natural time frames is tremendously stressful and invites undesirable behavior. Use a timer on their lighting and try to feed at the same time or times each day. Establish a reliable routine; fishes can tell the difference.

When adding potentially aggressive new stock or when territorial problems arise, disrupt the physical environment (rock, coral, and shell skeletons). This may seem antithetical to establishing predictability - it is. In certain rare instances you want to upset the status quo in the tank in order to disorient the existing community and its territorial dynamics. Changing the landscape can give the new arrival(s) a chance to settle into a fresh milieu.

Pay attention to the biological density of your system. What if, no matter what you do, World War III is still going on in your system? Your tank may be overcrowded. It doesn’t matter if your filtration can accommodate 10 more fishes; you’re past the behavioral maximum for your given microenvironment. It may be time to take

Nonfish specimens are also best introduced one at a time, with a week or two between new arrivals. Many invertebrates have chemical defense systems and can exude slime and mild toxins during and after shipping or handling.

Keepers of corals are increasingly adopting the practice of quarantining their new stock. Various infectious diseases can arrive with new specimens, and a week or two in a segregation tank is usually enough to be sure that you are not introducing a pathogen that might attack your existing corals. A rash of disease outbreaks in some of North America’s best-kept stony-coral systems in recent years has been dubbed rapid tissue necrosis (RTN) and has been attributed to an unknown pathogen, perhaps a strain of Vibrio. It typically arrives with small colonies imported from the wild and can sweep through an entire aquarium in a matter of days, leaving many species of small-polyped stony corals dead in its wake.

Many corals, both hardy soft species and exotic stony types, produce copious quantities of slime, and their arrival can overwhelm a display system and its skimming apparatus. This overload of protein, defensive chemicals, and perhaps bacteria, can make acclimating the new corals difficult and can be a setback for existing colonies. (Old hands add a bag of fresh, activated carbon to the sump or filter during these introductions or use an ozonizer for a few days following each new arrival.) Great care must be taken in placing any of the corals with offensive or defensive stinging capacities into your system. The tentacles of an anemone or stoney coral can rapidly attack and even kill neighboring invertebrates. In general, try to leave a good 6 inches of space between specimens.

Never place a new sessile invertebrate high in the tank, close to your lights. It is best to start incoming corals lower in the tank and slowly move them upward over a period of weeks, eventually finding a combination of light intensity and water flow that seems to suit them best.

As with fishes, it pays to pace yourself, and, whenever possible, to acquire new invertebrates one specimen or one species at a time.