Steve Schiff
Adaptation
April 19, 1998
How Species Adapt to Their Environment, and What This Means to Aquarists
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When we look at the natural world around us, we see hundreds of thousands or millions of species of living organisms, each one exquisitely adapted to its environment in ways both obvious and subtle.
When we attempt to keep these organisms in captivity, we change that environment in ways that are also both obvious and subtle.
Some organisms can adapt to the changes, and some cannot. Some do it better than others. Why is this so, and how, as aquarists, can we arrange matters so that the organisms we keep have the best chance of adapting to captivity?
Organisms can adapt in two different ways: short-term and long-term. Short-term adaptation affects individual organisms during their lifetimes, while long-term adaptation is an intergenerational phenomenon which operates on species, not individuals.
Both types of adaptation can have similar effects, but they operate using distinct and entirely different mechanisms.
When aquarists speak of adaptation, we are usually referring to the short-term form. This is the phenomenon that allows fish or other organisms that are accustomed to a particular set of water conditions to live under a different set of conditions.
For example, it lets fish which come from nitrate-free waters tolerate the accumulation of nitrate in an aquarium, and it permits fish that eat live fish, shrimp, or plankton in the wild to exist in the aquarium on flakes or pellets made mostly of wheat germ and fish meal.
The ability of an organism to adapt to environmental variations is determined by its physiology, anatomy, and biochemistry. These characteristics interact to enable the organism to exist under varying conditions of temperature, pH, redox potential, salinity, and hundreds or thousands of other variables.
These abilities have limits, of course, and these limits define what we call the "hardiness" of a creature. Organisms with a high tolerance for differing conditions are extremely hardy; while those with a lower tolerance are less so.
An example of an anatomical characteristic that allows an organism to adapt to conditions of low dissolved oxygen is the labyrinth organ of anabantoid fishes, such as gouramies and bettas.
This structure allows these fish to breathe atmospheric oxygen.
If the concentration of O2 in the water falls below useful levels, anabantids can obtain oxygen from the air, where its concentration may be 30 times higher than that in the water. Fish with this anatomical structure are tolerant of a wide range of dissolved oxygen concentrations.
Osmoregulation is a physiological characteristic that allows fish to adapt to varying concentrations of salt and other solutes in the water. Some fish - most marine species, for example - have delicately balanced osmoregulatory mechanisms, and can live only within a narrow range of salinity. Others, such as mollies, guppies, and brackish water fishes, have extremely flexible osmoregulatory systems, which enable them to tolerate a wide range of salinity.
Some of these fish can thrive in pure fresh water, full-strength seawater, or anything in between.
Some arctic fish species have special "antifreeze" proteins in their blood which lower its freezing point below that of the ambient water temperature. This allows them to inhabit very cold water which would otherwise freeze their blood.
This is an example of a biochemical characteristic that increases an organism's tolerance for extreme environmental conditions. When a fish moves into cooler or saltier water, it does not have to consciously adapt to the new conditions. Its body adapts quickly and automatically via the process of autoregulation, which is a phenomenon found throughout the living world.
Autoregulatory mechanisms are responsible for much of the short-term adaptability of organisms. Where do these autoregulatory mechanisms come from? Where, for that matter, did the labyrinth organ and the antifreeze proteins come from?
These are the long-term adaptations, characteristics which are developed by species and passed down from generation to generation through the process of inheritance.
All of these characteristics are genetically based - that is, they are coded for in an organism's genome, which is the molecular "software" that directs the growth and development, as well as the final attributes, of each individual member of a species.
Long-term adaptations develop via evolution of a species. Single individuals of a particular species do not exhibit long-term adaptation to any given environmental variable during their lifetimes. Instead, the evolutionary process operates on a species by means of natural selection of variations among individual members of that species. Over sufficient time, a species without a particular adaptation evolves into one with that adaptation. Note that it is the species which adapts in this long-term sense; individuals do not.
The adaptations that result from such evolution are the structural, physiological, and biochemical characteristics that tailor a species to its environment, and which, in many cases, allow for better, faster, or more efficient short-term adaptations. In this way, long-term adaptation can improve the ability of members of a species to make short-term adaptations.
Long-term adaptations occur much more slowly than short-term adaptations. Developed over many generations, they can be of much greater magnitude than their short-term counterparts.
Given enough time, long-term adaptation can produce entirely new species with entirely different characteristics than those of the initial species. Look, for example, at the history of the cichlid fishes.
Cichlids are "secondary division" freshwater fishes, which means that their ancestors were marine species. Modern cichlids are almost exclusively freshwater fish. The switch from salt to fresh water is a major adaptation which took a very long time to complete. Short term adaptation, although incomparably more rapid, is utterly insufficient to reverse the earlier trend.
If you think you can now plop a discus into your reef tank, you'd better think again.
An aquarist friend of mine once set out to prove that he could adapt a freshwater cichlid to marine conditions. Little by little, over a period of weeks, he added salt to the fish's water. Gradually the salinity of the water increased, until one day when I visited him he scooped up some water from the tank in a hydrometer and held it forth, proudly proclaiming "full-strength seawater!"
Sure enough, the needle of the instrument pointed to 1.023. The fish in the tank didn't look too happy - it sat near the bottom, fins clamped, colors darkened, barely moving - and it died a few days later.
That kind of adaptation requires hundreds or thousands of generations of evolutionary change - it cannot occur in a single individual over the course of a few weeks.
I have often recommended that aquarists tailor their fish to their tap water, rather than the other way around. By this I mean that we should keep fish that thrive under the water conditions that we can most easily provide for them.
Obviously, most aquarists do not follow this advice. To do so religiously would preclude the keeping of any marine species, among other things.
It's okay not to follow this advice, as long as you're prepared to do what's necessary to provide the appropriate water conditions for the fish you keep.
(This can entail a lot of work, as many saltwater hobbyists have discovered - but as long as you're willing to do it, go right ahead!)
What I cannot recommend is the intentional keeping of fish or other organisms under conditions significantly different than those they encounter in the wild.
Not only can this be cruel to the animals, but it is counterproductive to the goals of the aquarist, which are (presumably) to keep their pets alive, healthy, happy, and (if possible) fecund.
Because of their short-term adaptability, fish can live in water that is not optimal for them. (This is true of invertebrates such as corals as well.)
When we say that the pH range for a species is from, say, 7.5 - 8.5, what we mean is that the fish can survive for an extended period in water whose pH value is between these extremes. The optimum value, however, is not a range but a single number within the range at which the fish will do best. The optimum value for a given range of adaptability is determined by the biochemical and physiological makeup of the fish.
A fish's life processes, like those of any organism, consist of a vast interconnected web of chemical reactions, and like all chemical reactions, these are affected by the environment in which they occur.
Imagine a graph showing the typical behavior of a biochemical reaction under varying environmental conditions. Let the vertical axis represent the rate of the reaction - i.e., how fast it occurs, and the horizontal axis represent the value of an environmental variable - pH, for example, or temperature.
The graph will show that as the environment is varied, the rate of the reaction changes. Usually, the shape of the graph will be a bell-shaped curve.
At certain very high or low values, the reaction does not occur at all (or occurs at a negligible rate.) These extreme values represent the range in which the reaction can occur, and influence (but do not necessarily define) the tolerance of an organism for changes in a particular variable.
In the center of the range the curve has a peak. This represents the fastest reaction rate, and it occurs at the optimum value of the environmental variable for that particular reaction. (Note that this is not necessarily the optimum value of that variable for the entire organism - just for that reaction. An organism is the sum total of thousands of such reactions, all of which interact in complex ways.)
Just as each individual chemical reaction in a fish's body has a range and an optimum for each environmental condition, so does the fish itself.
The extreme values of the range represent the tolerance of the fish for changes in this particular variable, and beyond the extremes the fish cannot survive.
While the horizontal axis of a graph showing this relationship is the same as the one already described, the vertical axis is a more nebulous measure which we might call "Does Well" or "Does Best."
We cannot define how "well" a fish is "doing" by the rate of a particular reaction. How, then, can we define it? We can approach this question by asking another question: what do we mean when we say a fish is "doing well"? Well, mere survival is one measure (albeit a minimal one.) Being healthy, active, and free from disease are other criteria (although they are difficult or impossible to quantify.)
Growth is important (for fish that are still growing) - both the rate of growth, and the maximum size attained. The pinnacle of "doing well", from the standpoint of an aquarist, is reproduction - i.e., spawning, breeding, producing offspring, etc. If a fish is doing this, it's quite high on the "doing well" scale.
We're not finished, however. Reproductive success is a final criterion we might add to our evaluation. How do we define "reproductive success?"
By the number of offspring produced, the number that survive, how fast they grow, how "well" they "do," and their general quality - freedom from defects, disease, etc.
A fish with more, healthier, and faster-growing offspring has greater reproductive success than one which it beats in these categories.
Now we have a quantifiable criterion for reproductive success, since we can count offspring and measure their rates of growth and mortality. We can ask the question "How do factors such as pH, hardness, and temperature affect the reproductive success of various fish species?" and we can design a series of experiments that can help us answer the question.
I will tell you now that I have not performed any such experiments, nor do I know of anyone who has, so I cannot report any results. Anecdotal evidence accumulated by experienced aquarists seems to indicate that fish raised under suboptimal conditions tend to have reduced growth and lower reproductive success.
They produce fewer, smaller, and less vigorous offspring. This indicates that while the fish are able to survive and function, the suboptimal conditions yield suboptimal results.
Because of the difficulty of breeding many salt-water fish, reproductive success is not always a useful criterion for judging how well these fish are doing.
Of course, the very fact that breeding them is difficult indicates that they are not "doing" all that well! (Do you think it's difficult for them to breed in the wild?)
As regards marine species (fish and otherwise), we still have quite a ways to go before we can get their captive environment up to a level where they will breed freely and "do" their best.
Keep in mind that when a fish is short-term adapted to less-than-optimal conditions, it doesn't "do" the best it possibly can. (Think back to the poor cichlid "adapted" to seawater by my friend.)
By contrast, long-term adaptation changes the physiology of the species so that the conditions to which the species has adapted are now the optimal conditions, and fish living under these conditions feel quite at home.
The evolutionary change implicit in long-term adaptation has long been thought to require hundreds or thousands of generations over a period of thousands of years.
New evidence, however, is starting to show that the pace of change can be significantly more rapid than this, although it I still not anything you should expect to see occurring on a daily basis in your aquarium.
My personal opinion is that a short time period and small number of generations are inadequate to produce significant evolutionary change, at least in variables that affect the physiological functioning of a species.
It's easy enough to alter genes for fin size, body shape, or skin color, since these don't affect the basic life processes of an organism, but changes in the physiology would require changes in large numbers of interconnected reactions and their associated proteins, enzymes, structures, etc.
Because of their existing functionality and their interconnectedness, I don't believe these features can be altered that easily.
Alright, let's throw this open to questions.
Is there any example of a long term type adaption being breed into fish yet? Within the time frame that fish breeding has been done?
I'm not aware of any. Even though goldfish have been kept for thousands of years, and bred into all sorts of bizarre shapes, they will still revert to the wild type after a number of generations without selective breeding.
Why is mollies can be adapted to saltwater so easily?
Mollies are actually brackish water fish. They don't do well in pure fresh water.
Freshwater to marine, how long do you think a change could be done? Single generation, several, hundred?
I really have no way of knowing. I'm not sure if the fossil record indicates how long it took in the case of the cichlids. In fact, I'm not quite sure how they know whether a particular species of fish lived in fresh or salt water.
What do you recommend as a method to accumulate new fish into the aquarium? I have heard some people say to do the "float the bag on the water" thing, and others that despise that method and say to just throw the fish in the water, what do you think?
I don't think floating the bag helps much. All it does is equalize the temperature, but does nothing about the water chemistry. A better way is to gradually add small amounts of tank water to the bag. Another possibility is to put the new fish in a bucket, and start a slow siphon into the bucket from the tank. Whatever you do, don't add the bag water to the tank!
How easily do fish and corals and such adapt to our artificial lighting, is that a reason for so many deaths in the aquarium?
Lighting technology has improved greatly, and is constantly improving. It's not easy to duplicate the sun, in terms of intensity, at least. (Spectrum is not that difficult.) Fish are probably less dependent on the lighting than the corals, because of the zooxanthellae found in corals.
Where do guppies come from, that they have evolved to handle the extreme change from FW to SW?
Guppies come from the Caribbean island of Trinidad. I'm not sure if they are also brackish water fish, but it wouldn't surprise me. Remember that they are in the same genus as mollies.
Some fish are known to outgrow their surrounding, others don't, how does adaptation fit in here, will the fish adapt or will it die because it's needs of space are not being met?
The fish will die if its needs are not met. It has needs that include food, oxygen, clean water and certain water chemistry parameters. Space or room is actually a very minor requirement of fish. In fact, an experiment was done a few years ago in which a group of trout were raised in a glass jar, maybe one gallon in volume. They were fed normally, and a continuous current of clean water was run through the jar. (I.E., constant water changes.) The fish grew up to occupy the entire jar! They couldn't move, they couldn't swim, but they were completely healthy!
ChileRelleno said:
What is not said here is whether these fish were adults, if they were of average size for their species of similar age raised in ideal conditions.
Was there a control group raised under ideal conditions and what was the standard for completely healthy?
I can come up with many questions about this test. . . .
I'd be willing to bet that the fish were suffering some fin or skin abrasion, irritation and/or deformities due to the confines.
Many Asian fish enthusiast raise/keep fish in less than ideally sized habitats and perform the incredible amount of work necessary to maintain water quality. I've also heard that while reasonably healthy and of average adult size they have problems with injuries/abnormalities of their finnage.
I do acknowledge that stunting and it's related health problems up to and including death is primarily caused by 'sustained' less than ideal water quality/chemistry.
The point made here is that a fish will continue to grow regardless of it's habitat size provided all other necessary conditions are met.
Captive fish do not grow to the size of their habitat!
One unfortunate consequence of keeping a marine (or any) aquarium is that we have only a general idea of the conditions where the animal was taken from. Even in a marine environment there can be substantial variations (from the animals point of view). What do you do to offset this lack of knowledge of conditions to minimize the impact of introduction to the aquarium?
Do whatever you can to match the conditions you provide to those that the organism is known to require. This should emphasize the importance of researching the organisms you keep and learning about their needs.
Are tank raised fish better at adapting?
That's an interesting question. As I mentioned before, I'm not aware of any studies that have been done along these lines But anecdotal evidence says that they are. I'm not convinced, however.
Are you against saltwater fishkeeping in general?
Not at all. I hope that techniques of captive breeding improve to the point where most fish can be bred in captivity and not have to be removed from the ocean, because we kill so many of them that way. (This goes for corals and such even more!) But as long as aquarists are responsible, I'm not against keeping marine specimens.
There are a few fw fish that are able to adapt to sw, are there any sw fish that can adapt to sw, other than scats?
There are many brackish-water species. Scats are among them; so are monos (Monodactylus). The archer fish (genus Toxotes) is brackish. I think the mudskipper is, too. And don't forget anadromous species like the salmon. Eels, too, live in both for different parts of their life cycle.
How much of the FW hobby supply of fish is wild caught?
I don't know the exact percentages. There are some species, such as cardinal tetras, that are caught and exported by the millions each year. They are a major source of revenue for parts of Brazil. They're also fairly difficult to breed in captivity (which means we're not doing something right!) However, the majority of freshwater fish sold in pet shops are now captive bred. (That's not to say there aren't plenty of wild-caught fish available.)
What is the likelihood that a dwarf angel or other deep-water fish has been injected with a needle to assist bringing up from the ocean?
I don't know the "likelihood", but it IS sometimes done, and it's NOT very good for the fish. It may kill them; I'm not sure. But I believe it causes permanent damage. It also subjects the fish to the possibility of internal infection.
What specifics constitute responsible marine fish-keeping, and do you feel there should be any sort of regulation to ensure such responsibility?
The aquarist must know the animal he or she wants to keep. Study its needs and determine if you can provide them. Don't buy fish that only eat some rare type of sponge or something like that; they will starve to death in your tank, even though you surround it with what you consider to be food. Don't keep species that are rare or endangered. You should probably stay away from species that are significantly dangerous to humans, such as the dangerous cone shells (is that the textile cone?) Regarding regulation, I'm not very big on that idea. I'd much rather we police ourselves thhan have the government do it However, unless we (the aquarium community, including retailers and wholesalers, as well as hobbyists) do so, the government is bound to step in. If they do, many hobbyists and others involved in the industry will not be happy. But that's what governments know how to do -- regulate.
What is it that is injected into the fish to bring them up?
What do you mean? Do you mean when they are popped with a needle?
Yes that’s what was meant
They aren't injected with anything. The swim bladder is actually popped to relieve the gas pressure. That allows the fish to be moved rapidly up to the surface without blowing up like a balloon, but can cause permanent damage. I don't think it ever heals...
