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Posted by JR
on 1/31/2009, 1:50 pm
64.12.116.144
Through the eyes of a fry.
Life begins for a fry, of course, at the moment marked by the leaving of the egg. The emerging fry is not yet equipped to live life in a free swimming form as several important organs and structures are not yet developed. In effect, the fry is free from the egg but not yet developed to live in the outside world. The fry could not know that the breeder has taken great care to protect the embryo from pH shifts and other environmental changes that could effect water chemistry and kill the encapsulated fry before it even emerges. Disinfecting of all equipment has been seen to as well as treatment of the immediate surrounds to discourage parasite infection from parents as well as general fungal growth on the eggs themselves. Still some fry are going to be lost to gas bubble disease, infection and general inability to adapt to the outside world. This is a game of attrition in which many fry will be born and struggle while nature, who has no intention of allowing all to live, tests each individual for it’s worthiness/viability to live another day.
Our fry has been busy in the egg until now producing endogenous enzymes which gradually weaken the egg shell to allow for hatching. The breeder is an expert and assists the process by providing, among other things, an ideal temperature range for hatching. Too warm and our fry will emerge before it is developed sufficiently to have a chance for survival. Too cool and the hatching will be delayed and not move the process along at the rate of enzyme activity of the fry within.
Assuming our fry has merged successful from the egg, she will find that she is not able to swim yet. This is because she has not yet developed a swim bladder. So instead of investigating the environment, the fry in this larval stage will hang-- swim-- and hang vertically with an almost violent wriggling movement of the tail. When not attempting this awkward locomotion, the majority of the time will be spent hanging attached to walls and other surfaces. And like winter stasis that older koi go through, the fry must also be all about conserving precious energy as this is in limited supply at this larval stage. The larvae is fortunately blessed with an internal food supply. It is not like the energy supply it will one day store in liver, brain and white muscle mass. But rather it is a 3-4 day yolk supply used to continue the growth process of development as well as the operation/metabolic demand of the body itself. Pretty handy and certainly needed as at this point as our ‘gal’ has no mouth! In fact, she has no developed gut or gills as of yet! Instead the gas exchange function is right through the sheer tissues of the body that separate the ‘outside’ from the ‘inside’. This explains WHY fry are so very delicate. Everything must be exactly right or our fry will be lost. Oxygen levels must be high as the gills will not develop even under ideal temperatures for 1-2 days. At that point our fry will swallow the tiniest bubbles from the surface and fill her newly developed swim bladder with gas. She is now free to swim and investigate her environment which will be loaded with both prey and intense competition for that prey due to the massive number of siblings also present. Movement is still awkward however as the larvae only has one elongated fin and has not developed her ‘fin pairs’ like the one’s she will possess as a full fledged fry. The next few days and weeks are very important if the fry is to develop into an excellent nishikigoi adult. The fry MUST had adequate protein and good water conditions. This is because the fry is all about vision hunting at this stage. She needs to see her food and find it readily as her other sense organs are not fully developed. So adequate light is very important now. The breeder has provided the balance between adequate prey and limited water fouling that can result from unlimited feeding. Our fry at this stage is not at all like an adult koi. She is a pure hunter of live animal protein. Her gut is not like an adult koi and is very short like a carnivores and of a high metabolic nature. The ‘greens’ she will get come almost exclusively from the stomach content of her herbivore prey. She also acts like a carnivore in that she conserves energy and hunts, or even lays in wait, for swimming or moving meals.
The experienced breeder has thought all this through and has managed these needs, in some cases, for three generations of Japanese fish farming. So the methods are down to a science. Still, many things can go wrong that will end the life of our fry and it’s siblings that are out of the hands of our master breeder- rain, floods, freak weather changes, die off of food supply etc are all part of nature and part of the huge risks both breeder and our fry face.
Soon our fry is a master hunter and beginning to look more and more like a miniature version of a young koi. It’s skin is still poorly differentiated and the swimming style is very fry-like because muscle masses are just not there yet for adult type swimming gait. It would seem that the worst of survival challenges is behind our fry but in truth, the ultimate challenge is just beginning. A strange object has appeared in the watery world of our koi fry, and panic has entered the school. It is not like the momentary alarm that spreads through the school when ‘death comes from the sky’ or from the many giant hunters of the natural environment. This is something different- a wall that moves the school into a tight ever closing circle.
Now something very strange happens to our fry. It is moved from one strange environment to another until our fry finds itself back in home waters? The fry has survived the first of what will be many culling processes and is returned unharmed. Only this time, with less competition for the dwindling food supply. Indeed, even though the number of prey items has lessened, the lower competition rates and the ability to maneuver better compensate. Rapid growth continues to favor our fry’s survival chances.
If our fry could count, she would notice that what was once an army of siblings has dwindled down to something like five percent of the original population. The natural and man made live food supply has really dwindled at this point and many of the prey items don’t seem to be the main focus of the fry any more. Twice a day when the weather is good, a new food supply ‘appears’ both at the surface and sinking thru the water column. It’s scent is strong and the young fry has identified it as an excellent food source both from taste buds in its new barbels and also from memory, as it has already imprinted the sounds and shadows at a certain time of day, as those associated with a meal. It is awkward at first for our fry to feed off the surface as its mouth is located on the underside of its head. But the resourceful fry soon learns that after the sinking pellets are consumed, that there is more to be had at the surface. It learns to shift it’s continually deepening body into an opposite orientation and instead of ‘head standing’ with mouth positioned into the muddy bottom, it will now trail stand with the mouth making contact with the surface as if it were the muddy pond floor. The fish lives out that first year in a husbandry cycle. The culling has stopped and summer is a time of plenty. When the light gradually becomes less and the days get shorter, food supply once again lessens. The nights begin to get cold and the young koi can feel the change. It is soon netted and placed in concrete ponds under strange muted lighting. The water is warm but nothing like summer in the mudpond. There is no natural food or substrate to browse in.
( To be continued in part II)
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