Handling Delicate Larvae
Larvae - frequently asked questions
How to handle larvae.
Apart from being physically delicate the larvae are actually quite robust. They will tolerate very low dissolved oxygen, (DO), a wide PH range, are also tolerant to relatively sudden temperature variation, within reason. The larvae will die if you use nets. They will also die if the boxes are shaken, such as rough road or dropped box.
Do NOT use nets to transfer the larvae. We have tested many methods of transferring larvae with nets and all but one failed. The one successful method could not be repeated!
On arrival, the packing water will have high dissolved oxygen (...or at least it should be! ) it is important that the oxygen level be reduced to "normal" slowly. The tried and proven method is to open the bags, and, from the tank or pond you intend to release the larvae into, gradually add your water over a period of about half an hour until the water you have added is about four times the amount of water they are packed in. Your pond or tank water should have a dissolved oxygen, (DO) level of at least 8ppm. While doing this monitor the oxygen in the bags to watch that it does not drop too low. Once the DO is about the same as your water, add the bag of water with the larvae to your tank or pond. Do not pour the larvae. You can scoop the water and larvae from the bags and lower the scoop into the tank or pond but you must not pour the larvae. You can also lower the bag into the tank or pond and carefully, “slip” the bag out of the water. Once again do not pour the water with the larvae from the bags. The temperature in your pond or tank should be within 3 degrees Celsius.
We are often asked; How de we feed our Golden Perch, Jade Perch or Silver Perch larvae?
Hatcheries in Australia raise larvae of all these types of freshwater fish in plankton ponds. Larvae are introduced the into plankton ponds about three or four days after they hatch. Recently Ausyfish developed methods for tank rearing perch larvae. A special diet* is fed to the larvae for the first couple of days, then the larvae are weaned to freshly hatched brine shrimp.
* The special diet is a closely kept secret developed by Ausyfish after many seasons of testing.
Larvae usually take about 24 hours to hatch. We place our larvae in a tank in a dark room and shine a light in one side of the tank, if they all go to the light, this is when we put them in a large pond, we call a plankton pond. They should be attracted to light at day 3 and ready for food by day 4. This will change when the temperatures are higher or lower. Once they are attracted to light they can avoid predators in the pond. The pond is dried and then filled before the larvae are placed in the pond. This way there is plenty of zooplankton and not too many predators. We reduce the predators by passing the water through a 300 micron screen when filling the pond. Depending on temperature we fill the pond 1-2 weeks before we introduce the larvae.
We don't know what it is in our ponds that they eat that gives us high returns, however, it is widely accepted that fresh water rotifer is most probably their preferred first food. We use half acre ponds, about 2ML, which we fertilize and stock with 300,000 larvae. Sometimes we get up to 125,000 fingerlings back, sometimes as low as 4,000. Perch fingerlings are weaned in ponds. From about day 10-14 we start feeding our fingerling ponds with a commercial feed in dust form. At this stage they are about 10mm long. By about day 20-25 most of the fry are feeding at the surface. By now they are about 20mm It takes 6 to 10 weeks to grow the larvae to 4-5cm. They are fed twice daily until they are ready to harvest. The diet used is Ridley Aquafeed "Native Fish Starter Dust". This product contains 52% crude protein, 12% crude fat, and 1.6% crude fiber.
24c-26c is the best temperature for larvae. The larger fingerlings and fish grow fastest at 27c but will grow well as low as 20c