Why is that so Hard or Impossible?
I suppose I have mentioned a few times before that I love fish (and not only to eat) and that one of my hobbies as a teenager was to keep and breed aquarium fish. At that time the big challenge was the Amazon Blue Discus Symphysodon aequifasciatus, because food, temperature, aquarium plants, lighting, the pH and the hardness of the water – they all played critical roles. When captive breeding eventually succeeded, the price of this formidable species came down significantly. Another blue species (and there seems to be something with the colour of “blue”) is the marine Blue Tang, which has also been difficult to breed (like other coral reef species), but recently has become possible. But why do people want to breed fishes in captivity anyway? One of the main reasons would be the commercial aspect (some species are valuable as a food item and some in the aquarium trade as pets). But there is also the aspect of safeguarding that a species in the wild does not become overfished and ultimately extinct. A third reason would be vanity, namely to be the first person to succeed in finding a way to successfully breed a species that others had found impossible to breed.
But what actually makes it so difficult to breed a species, whether it’s a fish, a bird, a mammal or indeed any animal, in captivity? Looking at the two marine organisms that I had been associated with first, namely eels and rock lobsters (also known as spiny lobsters or ‘langouste’), it is mainly the fact that the larvae of these species spend a long time as marine plankton in the ocean and need a special kind of food that is difficult to prepare and to administer in captivity. Although one Japanese lab has succeeded to rear the Japanese eel Anguilla japonica from egg to a young individual, the effort in terms of costs and equipment is prohibitive and not yet a solution to reduce the collecting of eel fry and glass eels when they arrive from the ocean to enter freshwater and to curtail their sale to eel farmers who then fatten them up to turn them into young and sellable eels. A similar story is that of rock/spiny lobsters: for 20 years Japanese researchers tried to copy the entire life cycle from egg to marketable size in the lab of Panulirus japonicus and the best they could achieve was that about 1 out of a thousand larvae that hatched from the eggs in the lab and were then looked after for many years, would in the end survive to maturity. Commercially that would have been a flop and the research was terminated (at least in the lab to which I had sent a student to work in).
Not only are some aquatic species, and in case of the marine ones, hard or impossible to breed because of their long larval and planktonic phase (and also their size when thinking of tuna fish, the Blue Marlin or giant squid), but there are also the specific water quality requirements especially in case of the freshwater forms. However, some birds, mammals and other animals are equally well known to be difficult to breed in captivity and the cheetah and the panda are good examples. For the panda the extremely short oestrus period of 1-3 days/year is one problem, its choosiness regarding partner compatibility and its specific food requirements are another. Food for captive cheetahs is not a problem, but the very low sperm count in males is; the genetic relatedness of all extant cheetah individuals and the high mortality of the cubs are further notorious difficulties.
When it comes to birds (and apart from chickens and pigeons I never kept any), I heard that some parrots are not easy to breed and that especially their chicks require a great deal of care. I also don’t believe that it can be easy (or can be done at all) to breed swifts, house martins and swallows in captivity. Or, thinking of cuckoos that need a host species’ nest with eggs in it, so that they can add their own egg to those of the hosts. Adult albatrosses cannot even be kept in a cage, let alone ‘be persuaded’ to construct a nest and breed in it. In fact keeping and breeding sea birds in captivity would be a challenge best left alone and forgone in favour of protecting these birds’ wild breeding places. There are, of course, many, more species of animals that are inclined not to breed in captivity, but I realize that for some, sadly, captive breeding may be the only way they will survive as a species so that our children and their children can see them ‘for real’ and not just in the computer or books.
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