Thanks. Nine pages!
I went through my files and found an article on Aquarium Myths I wrote back in 1999, which in turn was based in part on some posts on Compuerseve's FISHNET forum back in the mid-1980's. I'm going to update that and post it in the library section here.....
Jay
TLDR --
Myths:
Iodized salt is harmful to fish:
After selling non-iodized aquarium salt in pet stores for 15 years, I strongly disagreed with the person who first proposed to me that iodized table salt worked just as well as the more expensive “aquarium salt”. Everyone “knew” that the iodine would kill the fish. I had a difficult time believing that this basic tenet of freshwater aquariums was false, but it is. You can safely add the same amount of regular table salt to an aquarium as you would non-iodized aquarium salt.
Aquariums can hold a set number of inches of fish per gallon:
You see this in books time and time again; “An aquarium’s holding capacity is 2” of fish per gallon”. Sometimes the number differs, in other cases the author adds refinements to the equation to take into account the aquarium’s surface area, filtration method, even water temperature. In every case, the equation has the same fatal flaw: With all else being equal, the waste output of fish, and their subsequent bio-load is not based primarily on the length of the fish, but more so their mass. An easy way to see this is to try to visualize the common formula of “two inches of fish per gallon”. Certainly a ten gallon aquarium can safely house 20, one inch long guppies. Now, even though the “inches of fish” are equal, try adding one 20” long pacu to the same tank and see what happens! As the length of a fish increases in a linear fashion, its mass, (and subsequent bio-load) increases by the length raised to the third power, multiplied by a constant (which varies for differently shaped fish). Another variable which also affects bio-load independent of the length of the animal is a given species innate metabolic rate; some species are more active, consume more food and thus produce more waste products than others of the same size.
Small aquariums are inherently less stable than larger ones:
I love this myth! Its one that every aquarist “knows is true”, and has been around since long before the advent of thermostatically controlled heaters, but should have been dropped once those devices were developed. You see, the only parameter, which is more variable in smaller aquariums than larger ones, is the effect that ambient air temperature has on unheated water. Small tanks will cool down quicker and heat up faster than larger tanks. Once thermostatic heaters were invented, this simply didn’t matter any more. Take the case where you have two tanks and the only variable is tank size – they have comparable filtration and other life support equipment (appropriately sized for each tank). If you then compare a ten gallon aquarium, which is housing “X” grams of bio-mass per gallon and 100 gallon aquarium housing the same ratio of bio-mass to volume, the biological stability of the two systems will be identical. This myth got its start in unheated tanks, but two other underlying problems have fueled it over the years. Notice that I said that the two tanks need to have comparable life support equipment. Very often, smaller aquariums have cheaply made filters and heaters, which negatively affect the overall stability of the system. In addition, it is much, much easier to overcrowd a smaller aquarium than it is a larger one; adding an extra 2” long swordtail to an already over-crowded ten gallon aquarium might increase the total bio-load of the system by 20%. The same fish being added to a similarly crowded 100 gallon aquarium would increase the total bio-load by perhaps 2%. The relative instability of these smaller tanks can often be documented, but the root of the problem is not directly correlated with the size of the tank.
Avoiding temperature shock is the main reason for acclimating fish:
A variety of acclimation techniques have been presented over the years, all with the hoped-for result of reducing stress and shock to an aquarium animal being moved from one aquarium to another. Some people have embraced this idea and taken it to the extreme. There was the aquarium keeper who would float bags for fish in his tank for eight hours rather than the 30 minutes recommended by the pet store; the reasoning given was “in order to expose the fish to the slowest possible change in temperature”. Never mind that in this case, the water temperature in the bag was fully equilibrated with that of the aquarium within the first ten minutes. Even if fish were exposed to a sudden change in water temperature, just how harmful would that be? As a SCUBA diver, watching fish swimming up and down along a ten degree thermocline with apparent impunity makes me wonder. I’ve even seen a damselfish diligently guarding its nest along an 8 degree thermocline in the Galapagos Islands. The continually changing water temperature affected neither the fish nor its eggs.
Overly long acclimation times generally do more harm than good. Take the example of fish, which have been in their bags for over 24 hours. Typically, the pH of their water will be very low, while the ammonia concentration will be high. As it turns out, ammonia is much less toxic to fish at a low pH. Imagine what happens to those fish during a lengthy acclimation; as the carbon dioxide is driven out of the shipping bags, the pH rises. Even though the aquarist is slowly adding tank water to the bag, it isn’t happening fast enough to dilute down the ammonia before the rising pH makes the ammonia toxic enough to kill the fish right in the bags. In other cases, the stress imposed on certain shy fish by restraining them in a clear bag at the surface where they cannot hide is greater than just releasing them so they can seek a secure hiding place. Generally, acclimation times of more than 30 minutes are unnecessary and potentially do more harm than good.
Fish only grow in size to fit their aquarium:
Most intermediate and advanced aquarists, (or anyone who has ever purchased a pacu) knows this statement is more accurately stated as: “Fish grow rapidly to a maximum size for that aquarium, then the growth rate slows a bit, but they still outgrow that aquarium if it is in their genetic makeup to grow that large”. Of course, the irony of this seems to be that this slowing of the growth rate only gives the aquarist time to save up money for a larger tank. When the purchase is made and the fish is placed in its spacious new quarters, its growth rate again speeds up until it again is about to outgrow its new tank!
Ultraviolet Sterilizers eliminate diseases from aquarium water:
Ultraviolet units have absolutely no affect on disease organisms, which live on the fish directly and do not need to leave the fish during some part of its life cycle (some protozoans, trematodes and most pathogenic bacteria). Other parasites such as larger protozoans and all multicellular parasites too big to be killed by aquarium-sized UV units. The expected benefits from a properly operating UV sterilizer would be a lowering of the free-floating bacterial and protozoan populations, as well as fairly good control (close to 100%) of these organisms when water flowing from one tank to another first passes through the UV sterilizer. Side-stream sterilization, where the irradiated water is returned to the same tank is was taken from is always less than 100% effective – too many of the target organisms are able to escape passing through the unit and are able to continue to reproduce.
Predatory fish, which only accept, live foods:
I remember in the 1970’s, thinking that lionfish would only eat living fish. Sure enough, all my lionfish would greedily accept “feeder fish” from the very start, and would always steadfastly refuse anything else once they have become accustomed to that diet! This was really just a case of a self-fulfilling prophecy, I expected them to eat only goldfish and sure enough, that’s what they became accustomed to!
There are a variety of reasons why non-living foods may be preferable; lower cost, ease of storage, ability to supplement with vitamins, etc. Can every species of fish be “trained” to feed on non-living food? It seems that almost any species can, if the required amount of effort is made. The basic trick seems to be to begin feeding the fish an acceptable living food, but very soon after, begin inter-mixing some freshly killed individuals of the same food. As soon as possible, switch the animal over to all dead food, then begin offering slivers of the prepared food made the same size and shape as the accepted prey item. This technique works very well for anglerfish, lionfish even trumpetfish. In some cases though, the training effort is simply too great (such as with shrimpfish, seadragons and leaf fish). I once had a report that a person had gotten their seahorse to feed on flake food using this method, but I never saw this first hand, and would hate to create another myth by putting too much stock in that story!
Snapping shrimp can break aquarium glass when they snap their claws:
I first heard this when I was about 12, when I purchased a small snapping shrimp and was warned by the salesperson that they “have been known to crack the glass of tanks”. After adding the shrimp to a small aquarium in my bedroom, I had a rough couple of nights, jumping up to check the tank every time I heard a snap. The glass never did break, nor have I heard any first hand accounts of this phenomenon (its always, “It happened to a friend of mine’s brother). There are reports of snapping shrimp stunning fish which swim by, so there is apparently some force behind their “pop”, just not enough to crack glass.
Flying gurnards taking to the air:
These bottom dwelling fish were pictured by early naturalist artists as being capable of gliding through the air like flying fish. In reality, these fish extend their huge pectoral fins in an attempt to make themselves look too large to eat by potential predators. As recently as 1976 an eminent fish taxonomist wrote that these fish are “supposedly capable of gliding short distances”. If one considers jumping out of a tank onto the floor as “gliding a short distance” then perhaps this is true, otherwise we should consider this myth dead and buried.
The following are a few additional statements I find suspicious, and although not yet disproved, they might in time end up as aquarium myths:
Mangrove seedlings help maintain marine aquarium water quality:
I can’t recall how many dead and dying mangrove seedlings I’ve recently seen offered for sale, floating jammed into pieces of Styrofoam in dealer’s holding tanks. Keeping mangroves healthy in aquariums is not a simple matter; they are prone to developing scale insect diseases and require very high light levels. Even if the plants do thrive, the argument that they will actively remove organic waste products from the aquarium’s water is difficult to prove. In one case, a 200-gallon exhibit containing three large, actively growing mangrove trees had been set up for two years. It did have a fairly heavy bio-load of fish, but an orthophosphate reading of 7.5 mg/l was totally unexpected based on the supposed nutrient removal ability of mangroves.
Red-rimmed batfish feeding on bananas:
Years ago, a person wrote an article for his local aquarium club recalling his experience feeding bananas to a pair of red-rimmed batfish (Platax pinnatus). His argument was that since batfish are residents of mangrove swamps, they should be well adapted to feeding on plant material. By that same train of thought, lions should be well adapted for feeding on grass because they are found in the grasslands of Africa. In addition, the red-rimmed batfish is a resident of deeper coral reefs; it is the round batfish, (Platax orbicularis) which is found as juveniles in mangrove areas. I’ll admit, I have tried feeding bananas to red-rimmed batfish on three occasions (but have never gotten one to accept any). As the article goes on, the author reports that the fish grew to a height which was 2” taller than the aquarium he reported keeping them in – it’s possible that the entire article was some sort of practical joke. The danger is that this article still gets referred to once in a while, it is archived in an on-line computer database, and people keep finding it when they run a search for information about this species.
Huge fish thriving in a small aquarium:
From time to time I get reports such as a three foot long snakehead living in somebody’s one foot wide by four foot long 55 gallon aquarium. As I’ve previously mentioned, the “fish growing only to a size to fit the tank” statement is a myth, as these reports seem to bear out. Either these fish have an amazing ability to survive in horrendously undersized aquariums, or people’s ability to judge the true size of their fish is impaired, or a combination of both. That brings to mind the story of the “Florida tape measure”. It seems that some fish dealers have in their possession, a magical tape measure: nurse sharks always tape out at 14” – even if they measure 24” when you pick them up at the airport. For other species such as angelfish, the same tape measure that the collector used on the nurse shark will gives them a measurement of 8” for a show-sized queen angelfish that ends up being about the size of a half dollar when you unpack it.
Lee Chin Eng Natural system:
I remember seeing the photographs of Mr. Eng’s tank in hobbyist publications in the early 1970’s, and wondering why I could not re-create a similar aquarium. He was reportedly able to keep all manner of fish, corals and other invertebrates in aquariums with just a slow trickle of air. Mr. Eng has evidently passed away, so we really only have his photographs to document his systems. I would urge people to study those photographs very closely; quite a bit can be deduced from them by careful observation: A lot of the photos show huge numbers of shrimpfish along with damselfish, clownfish and batfish. Anyone who has successfully kept shrimpfish knows that they do best if fed live mysid shrimp, and cannot compete against other fish for live food. My strong opinion is that Mr. Eng added these shrimpfish a short time before taking the photo – and may have done the same with some of the more delicate invertebrates in the tank. Other pictures show corals placed in unnatural positions, showing no evidence of any in-situ growth. Many of the other organisms are hardy species (at least for the short term) such as feather dusters, carpet anemones and red starfish. My hunch is that Mr. Eng set up aquariums with live rock and hardy animals, and then just prior to being photographed, he “spruced the tanks up” by adding a few showy, but delicate species.
Flying hatchetfish:
This is a rather “slippery” tale. Every once in a while I’ll come across a reference regarding the flying ability of the South American hatchetfish. That’s right, I said FLYING not just gliding. Apparently, the argument is made that the deep breasts of these fish serve as anchor points for huge pectoral muscles, which the fish uses to vibrate its fins and achieve a sort of powered flight. One description I read told of a school of these fish taking to the air and passing by the observer’s head making a loud buzzing sound. Although these fish are well known for their ability to jump out of tanks, I’ve never seen any direct evidence of powered flight. Perhaps they need a longer runway for take off? I’ve toyed with the idea of adding a school of these fish to a 20,000 gallon reservoir, and then give them a scare and see if they will fly under those conditions.