Myths in Fishkeeping III
Myths in Fishkeeping III
Written by Saturday, 29 November 2008 00:00
| Article Index |
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| Myths in Fishkeeping III |
| Page 2: Conditioning and Triggering |
| Page 3: F Generations |
| Page 4: Individual Behaviour |
| Page 5: Notes |
| All Pages |
Breeding a species in captivity is considered a success. Quite rightly so; breeding offers us a wealth of information which would otherwise be unavailable. The fact that a species breeds in captivity is also taken to be an indication of correct husbandry. Under the circumstances it comes as no surprise that a number of hobbyists seek to breed their fish; high demand for information is usually matched by supply. There is no reason to doubt that most information available is accurate. Yet not all breeding reports are necessarily thorough, nor do they record accurately everything that has happened prior to a breeding taking place. Most importantly we all record things that seem important to us - and these do not necessarily coincide with the things that may or may not trigger a species to spawn. Hence myths around breeding originate mainly by establishing causal links between aquarists practices and fish behaviour.
Let us look at some myths around breeding:
Selecting the Stock
Hobbyists wishing to breed fish are often looking for wild caught specimens. In the old days this was quite understandable: tank bred individuals were not commercially available. Today the situation has changed. A number of hobbyists are, justifiably, averse to the idea of buying farmed fish due to the hormones and antibiotics these fish have been exposed to prior to being shipped. Having said that, there seems to be no reason to continue to deplete natural resources when good quality fish, bred by fellow hobbyists, are or can be made available.
Still, tank bred fish are considered by some as “inferior” breeding stock to their wild caught conspecifics. This position is supported by a variety of arguments:
- wild caught specimens are genetically unrelated and thus during reproduction the possibility of homologous unwanted traits is minimized,
- captive bred specimens are somehow thought to be more prone to mutations or be potential carriers of unwanted traits
- in some cases fish collected from the wild show better patterns or more vivid colouration. It is expected that these traits will be maintained in the tank and will be passed on to the offspring of these fish.
- wild caught fish are thought to manifest a more 'natural' behaviour by comparison to their tank bred conspecifics.
Lets take these issues in turn.
A. Wild caught specimens are genetically unrelated and thus during reproduction the possibility of homologous unwanted traits is minimized
We would question the validity of the term “genetically unrelated” in this argument, especially when it comes to shoaling fish or generally fish collected from the same spot. For obvious reasons interbreeding is as likely to occur in nature as it is in the home aquarium with shoaling fish. Chances are that fish living in colonies or sharing the same “spot” may also be genetically related. Subordinate males who are evicted from the original colony will eventually move further down the river or pond and occupy a different spot. As this spot is not usually miles away from the birthplace of these males – the fish will naturally select the first “safe” spot on their way - the females which came from the same brood or lineage are quite likely to become the males’ future partners. In fact, this is how colonies develop.
Similarly fish netted at a young age are more likely than not to be found with their siblings, who are also collected at the same time from the same spot. These fish, though coming from the wild, have got high chances to be genetically related.
Admittedly, given the process taking place prior to shipping, chances are that the fish will get mixed up and that the group an aquarist will purchase may not be – or may not be in its entirety – consisting of genetically related individuals. Having said that, each individual in the group may well be considerably interbred so in this sense the hobbyist does not avoid “risks” related to interbreeding by purchasing wild caught individuals.
If fish from the same lineage do interbreed in nature and still survive healthily for centuries, is that not an indication that interbreeding is not as dangerous for the species as it is made out to be? From this point of view a similar result to acquiring wild caught individuals can be achieved by acquiring aquarium bred stock from different hobbyists, or from the same hobbyist assuming they can provide stock which comes from different parents.
B. Captive bred specimens are somehow thought to be more prone to mutations or be potential carriers of unwanted traits
Mutation is an issue which merits really detailed scientific analysis. It is beyond the scope of this article to achieve this. Having said that, it is worth clarifying certain issues concerning mutation.
Mutation is defined as a permanent change in the DNA (or, rarely, the RNA) sequence of a gene. In living cells such chemical changes happen quite frequently, particularly during cell reproduction. Some of these changes are subsequently corrected, programmed to die (apoptosis) or simply not viable so they do not result in mutation. Others are not.
Mutation has usually got negative connotations mainly due to the fact that some of the factors causing it adversely affect a living organism. Such examples include radiation, viruses, or chemical mutagens. However, the ability of an organism to mutate is the cornerstone of survival: mutation is nature’s way of adapting to environmental changes thus ensuring evolutionary change. Very simply, there would be no speciation if there were no mutations.
Our first argument therefore is that a mutation is not necessarily something bad. In fact quite the opposite is true; viable mutations can be observed in the fittest individuals – that is why these survive while their conspecifics do not. (1) Most of the fish we keep now are mutations of some remote ancestors. The idea that by selecting wild caught individuals we are ensuring that only archetypal fish swim – or will swim in future - in our tanks is simply ridiculous.
Mutations exist in nature of course. (2) The hobby has selectively picked some of these to value and prize and others to avoid – without specifying any reasons for this:
“Reprinted from [Angels Plus] website is this warning. Steve Rybicki states, "There are two other significant genes that affect the look of angels. One is Stripeless and the other is Pearlscale. These are not color genes but can have an effect on the look of the color genes. The other major gene people are concerned with is Veil, which simply affects the length of the fins. All angel hybrids are derived from the above listed mutations. Since you can have literally dozens of possible hybrids, to reduce confusion, I use the names that were originally given these fish by the people first making the cross and publishing the results. When I cross a Smokey with Pearlscale the result is a Smokey Pearlscale, not a Blue Diamond Crystal. Beware of the person renaming angelfish. Why would they do this? It couldn't be that they want to fool you into thinking they have something different so you would spend your money there, could it? Granted, not all Gold Marbles Pearlscales are identical. Some have been selectively bred to look a little different from other Gold Marbles Pearlscales, but that doesn't make one a "Red Headed Tangerine" angel unless that is the generally accepted name for that hybrid.
Every worthwhile mutation is written about in a national publication shortly after introduction to the hobby (within a few months). Ask what issue it is in if someone claims to have a new mutation that is worth having. If it's just a hybrid the person has, then you can make it too, if you want. By the way, people do not "develop" mutations.” (3 - emphasis added)
Along the same lines in L46s broken line Hypancistrus zebra (L173) are commanding an extortionate price by comparison to the already pricey individuals with regular markings. Koi are colourful mutations of the wild carp (Cyprinus caprio) while our known and loved goldfish are mutations of the original wild brown type.(4) The price for an albino Acanthicus Adonis is rocket high by comparison to the price of fish with the normal melanin pattern.
A mutation may be an indication of adaptation to a new environment. As tank environments are radically dissimilar to natural habitats it is to be expected that after several generations traits that would not survive in the wild may prevail in a tank – this is called adaptation. This may or may not be visible to us. For instance, following observations, fish farms are now looking into ways to avoid farmed fish escaping in the wild to breed with their wild conspecifics. A major risk of farmed fish interbreeding with natives is that their offspring is "less genetically adapted to survive in the wild”. (5) Adaptation may include loss of characteristics which are no longer required or development of new characteristics required for successful survival in the new environment. Admittedly in any of these cases the fish hosted in our tanks may look dissimilar to their wild conspecifics. But it is a fallacy to believe that if there are no visual differences our fish are the same and behave the same way with the ones swimming in rivers or lakes.
As a closing remark we would observe that mutations are subdivided into germlike and somatic. Somatic mutations are not inherited by descendants in animals. In other words, unless we breed an individual with a mutation we cannot know whether this mutation will be passed on to its offspring or not. Similarly, it is quite likely that a fish with no phenotype changes (i.e. not showing signs of mutation) may beget offspring with a mutation. This is not something we, as aquarists, can always know as a mutation canot be “seen”. The trait it encodes may (or may not) be visible. Accordingly a wild caught individual is as likely to produce offspring with mutations in our tanks as a tank bred individual.
According to this second argument (b) preferring wild caught individuals as opposed to tank bred ones is also justified by considerations regarding the health of the future potential offspring. Tank bred fish are allegedly more prone to produce deformed individuals or otherwise potential carriers of unwanted traits.
There are two issues here. The first is the extend to which wild caught individuals may - and are as likely to - produce offspring with deformities as tank bred individuals. We also need to look at the underlying reasons for tank bred fish producing deformed offspring.
A deformity is "a major difference in the form of body part or organ compared to the average shape of that part. Deformity may arise from different causes"; natural causes include "genetic mutations, damage to foetus or uterus, complications at birth, a growth or hormone disorder". (6) None of these causes are particular to tank environments, with the notable exception of disorders due to poor diet. Given the levels of pollution, change and exploitation of some natural habitats it is safe to assume that poor environmental conditions may apply equally to both tank bred and wild caught individuals.
Deformed individuals are also born in the wild. If the deformity is such that makes an animal non-viable or simply less competitive than other members of its species it will lead to its death. Selection of individuals to sell on to hobbyists also ensures to an extent that only non-deformed specimens find their way to hobbyists’ tanks. This does not mean that deformed individuals do not exist in nature, or that wild caught individuals do not produce deformed offspring in tanks or in the wild. (7) It simply means that the latter do not usually find their way to our tanks. The same is achieved through culling of tank raised or farmed stock, which is what reputable hobbyists and fish farms do.
Deformities due to poor diet mainly occur in the tank. Tank bred fish are subject to a different diet and environment than fish in the wild. This in itself is a critical factor in them possibly producing offspring with deformities. Studies have shown that Brachydanio rerio (zebra danio), if fed commercially available tropical flake foods, will produce offspring with deformities. Feed them live foods and these animals will produce healthy offspring. (8) Again a common deformity of larger tank bred fish is stubiness. Rather than growing in length, fish with this deformity grow in height. This has been observed time and time again with fish growing up in crammed conditions or in unsuitable (small) tanks for their size. (9) Since, however, these and other offspring deformities are the result of environmental factors, wild caught animals in the same environment would also produce deformed offspring. Avoiding tank bred stock will not address this issue; ensuring that the environment is suitable for our fish will.
Another difference between wild caught and tank bred fish is that tank bred fish have not gone through the natural selection process which takes place in the wild. A good number of hobbyists are still trying to bring up each and every individual born in their tanks; culling is considered either ‘unethical’ or hard to do to fish one has brought up in their own tank. As a result individuals with traits which would be eradicated in nature do grow to adulthood in tanks and are subsequently given opportunities to spawn, thus passing some of these traits on to the new generation.
It should be noted that none of the issues discussed above concern the genome of tank bred fish; both are related to human practices in fish keeping. Obtaining fish from reputable sources, including serious aquarists, would therefore eliminate these problems.
It is important to remember that there is no guarantee that wild caught individuals will produce healthy offspring in tanks or in the wild for yet another reason: human intervention. With pollution rising in aquatic habitats a considerable number of individuals suffers chronic toxicity. In effect, what is happening in the wild is precisely what we are stipulating could be happening in our tanks due the heavy or consistent use of chemicals. Pollution of biotopes will affect fish reproduction in ways similar to these that chemicals in tanks are affecting tank bred fish. The effects of such toxicity may be apparent immediately or after a period of time (acute or chronic toxicity). In practical terms, therefore, an aquarist cannot be certain whether a particular deformity is due to tank used chemicals or some kind of environmental pollution in the wild, unless carefully designed experiments under controlled conditions followed by DNA analysis are conducted.
Both wild caught and tank bred animals are likely to produce deformed offspring in tanks for one more reason. On the whole, if kept properly, fish live longer in tanks than they do in the wild; this is due to the lack of competition for food or space as well as the lack of predation. We have observed larger proportions of deformed animals to be born to “aged” couples (Neolabrologus Brichardi, Trichogaster Trichopterus etc) who have previously had very healthy spawns for years. We have not got enough evidence to be able to explain this phenomenon; it could be due to the age of the parents or to their long exposure to tank conditions. Similar evidence from the human species though indicates that age could be the critical factor. In any case, the same phenomenon applies to both tank bred and wild caught individuals.
C. In some cases fish collected from the wild show better patterns or more vivid colouration. It is expected that these traits will be maintained in the tank and will be passed on to the offspring of these fish.
The third reason which is cited in support of preferring wild caught fish over tank bred ones is that in some cases the fish collected from the wild show more vivid colours. This has been proven to be true in most cases. However it has nothing to do with the genome of the fish; it is largely the result of environmental factors, including feeding patterns in the wild. In some cases it has been reported that fish which showed remarkable colouration lost it in captivity since their living conditions (light, food, environment) had changed. Ad Konings reported the discovery of a golden morph of Dimidiochromis compressiceps in Lake Malawi (close to Taiwan reef) which rapidly lost its golden colouration when kept in a tank. It goes without saying that the vibrant colours will not show in any generation (F0 or subsequent spawns) when these fish breed in captivity. To reverse this remark, vibrant colours or even special traits can become visible on fish of any generation if the right elements become available in their tank, being it food, micro-nutrients or even correct water parameters. (10)
To conclude, the only clear advantage that wild caught individuals have over tank bred ones in terms of breeding is that we can safely assume they have not been subjected to poor husbandry and so they are not likely to produce deformed offspring due to such husbandry. This is also very much the case with tank bred fish from reputable breeders. In addition tank bred individuals are better suited to live in tank environments, more resilient to the plethora of bacteria existing in these environments, less likely to encounter the same problems that wild caught individuals have during acclimatization and most importantly less likely to introduce parasitic infestations in the tank.
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