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Author: Bart van Dijk
Title: Triggers

Summary: After giving examples of animals reacting to their environment, Bart discusses what killifish eggs have to "think about" before they hatch, and what you can do to convince those in your tanks that they should  hatch.
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Date first published: Nov. 2000
Publication: Vancouver Aquatic Hobbyist Club newsletter.
Reprinted from Aquarticles:
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by Bart van Dijk
First published in the newsletter of the Vancouver Aquatic Hobbyist Club

The guinea pigs we bought on impulse. They did not have a home yet and the cardboard box had to be cleaned. I blocked the kitchen door and let the guys loose. All during the cleaning I heard alternately subdued noises and very frantic nail scratches on the tiled floor. I stood there utterly amazed. "What were these guys doing?" - they would walk calmly out from under the fridge and then make a mad dash back underneath, over and over again. It took me an hour of watching to realise that they were obeying their built- in command: "Know your way home from anywhere so that you can make it from, in this case, anywhere in the kitchen to under the fridge." Care to guess how long it took me to catch the guinea pigs? Yes it might have taken two hours that one night, but once I learnt to whistle the very high sound that guinea pig mothers use, I found I could freeze them to the spot no matter what they were doing, and they never figured out that it was not their mom for all the six years they were our pets.

A friend of mine in the Queen Charlottes worked as a faller, cutting down huge trees. During lunchtimes he delighted in observing the animals around him. He managed to just about tame a raven, who would come every lunchtime. He started wondering how this raven could manage to fly through all those branches and never hit anything. As his cut progressed away from the raven's area he began to notice how the raven did not fly to him any more "as the crow flies" but was zigging and zagging, and once the idea hit him it was obvious: the raven was flying the old flyways through the now non-existent trees.

Spotty our terrier cross was a bright animal; show her a trick and almost straight away she would do it - learning ability bar none. Yet for all of her eighteen years she would bury the excess food in her dish by scooping the non-existent dirt from the kitchen floor with her nose. Each night she would lay down all the standing grass in her bed by turning around and around. Reading every other dog's territory with her nose was of utmost importance on our evening walks, but it was useless information to her because she knew full well that our lot was her lot, and she knew the boundaries to the nearest inch. She knew that severe penalties always followed crossing the line, but any cat in full flight would make her forget.

* * *

The countryside is bare and boy is it dry… The rain begins to fall, and the dried up ponds and puddles are actually beginning to show a little bit of water….. The little killifishes in their eggshells have been waiting for this ! Depending on the area where they live, they have waited two months to ten months, and quite often when the previous year's rains failed to come, they have been waiting between fourteen and twenty two months.
But the first rain brings with it a huge dilemma for these guys. Is this the rain that will continue and put enough water in the pools to make a full life cycle possible, or will it dry up shortly and cause certain death if you have hatched? A tough decision to make, especially when you are inside a half millimetre eggshell, stuck in the mud.

If a "small" rainfall occurs you will get wet alright but that is about all; everything else stays the same:
1) The temperature of the water around you will be about the same as the mud you are in, instead of dropping significantly.
2) You did not get tossed around by the little streams in the pool.
3) The infusoria have not "hatched" in the huge quantities that consume most of the oxygen, before the copods, daphnia, start eating them.
4) You cannot feel any microworms moving through the mud.
5) The water depth does not cause any pressure on your egg shell yet.

… So there you go, measure all parameters until you are absolutely sure. However there are always "buts"...
-If you wait until the water depth is too great you will not be able to make it to the surface for that vital first breath to blow up your swim bladder (if you don't make it you will always be a belly slider).
-If you wait a few days you might just be out in the cold when it comes to staking out a territory - the guy who gets there first is usually more determined and manages to hang on. And what is more, you might not be able to complete a full life cycle at all. Everything might be dry again before your own eggs are safely back in the mud again.

* * *

O.K., so YOU buy a pack of eggs at our Auction. Know now that you have to convince these little fish that the time is right…..
First you have to make sure the eggs have been dry for their normal dry period and then the battle is on:
- You put the peat with the eggs in a flat dish, cover them with about two inches of, for them, cold water of about 55 degrees. Good for you, you have now convinced the daredevils (say about 20%) that this is the time, and you have made sure that they can get to the surface for that gulp of air.
- But you would have convinced another 30% if you had shaken them around a bit, so gently spend some time breaking up all the peat lumps.
- Unlike "regular" fish, killies don't have yolk sacs, and you have to feed them immediately on hatching anyway, so a good dollop out of your infusoria culture will lower that oxygen content, and will convince another 20% to hatch. Similarly a finger full of microworms will improve your hatch rate once again.
- But it takes drying the peat once again after the first hatch, keeping it dry for about a month or two and going through the same procedure again to finally convince the diehard pessimists to come out also.

Good luck! To see all those guys hatch, usually the day after you put the water in, makes it all worthwhile.

A huge thank you to all the Killie Club members who must have become very tired of answering all my questions during the past two years. I promise to keep on learning more and more by observing my own killies. I will keep on varying their environment until they are as happy as they can be.