The following information is the results of research by Brett Herbert. The work was done at Freshwater Fisheries and Aquaculture Centre Walkamin Far North Queensland, Australia.
The following details the method we have used to wean golden perch fingerlings. You may find it of use if you are to wean fish this year. Our survival rates in mass rearing have been good, with up to 98% survival. Fingerlings 20-25mm total length do well, using a 1mm skretting salmon crumble starter diet. The Ridley’s starter diet is too big. If you get bigger fish a bigger crumble could be used, but 1mm will get you through. It is best to have all the blocks made up beforehand. We work on about 50-60mL plankton slurry per 1000 fish.
Our most successful method to date is as follows:
- On receipt of fingerlings feed frozen plankton, until fish are through transport shock, quarantine, and prophylactic treatments are completed. This may take up to a week (usually a couple of days). Advised treatment is 70ppm formalin with 10‰ salt for one hour. The fish must be watched carefully for the duration of the treatment and strong aeration maintained.
- Start feeding frozen blocks of plankton slurry. We habituate the fish to being fed in a specific place in the tank at specific times. We feed three times a day. Water and aeration are turned off so there is no current in the tank. Frozen blocks are placed in a plastic mesh basket (gutter guard or similar), hung on the side of the tank at the water surface. Plastic mesh is about 10mm2. The cover of the tank is pushed back a little on each feeding occasion as the fish don’t like bright light. The amount of food required is determined by observing the amount of plankton left circulating in the water thirty minutes or so after feeding. It is important to know how much they eat so as not to feed to excess during weaning.
- Fish were observed feeding. Once the majority of fish were rising to the blocks and actively feeding, the weaning process began.
- Frozen blocks of plankton/crumble mix (we use 1mm skretting salmon starter crumble) replace the plankton blocks. The ratio of plankton: crumble is reduced by 10% each day. We use volume to measure, starting with 10% crumble to 90% plankton, reducing plankton and increasing crumble by 10% each day. Use a slurry of plankton. The higher proportions of crumble mix will be dryish, do not add water when mixing as if you do it stays in a lump and does not fall though the mesh. It also fouls the water very quickly if too wet. Over mixing makes it go to a gooey paste which does not work. It is best to mix the fresh, chilled plankton with the crumble. Do not freeze the plankton and thaw it for mixing. If the mix is dry and unlikely to hold together (usually only the 80% and 90% crumble mixes are like this) you can add water after the mix is partly frozen, and then freeze it completely. That way you are not mixing water and crumble excessively, and it will behave well.
- Weaning takes 9 days. The crumbles are then fed by sprinkling on the surface in the same place as the basket was. Observe the fish-they should still be coming in to this area to feed. We continue feeding crumble alone for two weeks during which most non-feeders will die off.
Artemia could be substituted for plankton if desired. However, Artemia fouled the water more quickly than plankton.
Cleaning on a daily basis by scrubbing the tanks is essential. Flushing just after feeding is essential due to the fouling effect of the moistened frozen crumbles. Plankton-crumble mixes of 50-80% crumble foul the water worst.
The plankton size should be <1mm and >200mm (for 25-35mm fingerlings). Our plankton of this size was primarily Moina, juvenile Daphnia, and copepods. We make the mixes up each morning with the fresh plankton. We chill it first so it is cold and use crumble stored in the freezer. The final mixes (80 and 90% crumble) will probably not hold together, add water in the mould when freezing. Put the mesh bag in and then sprinkle the crumbly mix above the bag. Only mix until the plankton and fish food are well combined-too much mixing and the fish food goes like mud. It will not break up and fall through the basket.
The plankton slurry is a consistency that will hold its shape for a short while-if you take out a spoonful and place it on top of the slurry it will gradually sink in. If it disappears straight away it is too thin. Likewise, if a spoon stands up in the slurry it is too thick.
Introduction of fish into ponds where any other food source is available may result in the fish going back to alternative food. We have fish in cages in ponds feeding on artificial food.
All attempts at weaning fish “cold turkey”, with or without presence of weaned ‘trainer fish’ were unsuccessful. We had a maximum survival rate of 20%. We did find that these fish grew as fast as the best of the weaned fish. This suggests that possibly some fish are predisposed to eating whatever is available, and these are the fastest growing.
If you have any questions, or would like to clarify any points on the above, do not hesitate to contact us. (Contact details at the bottom of this page)
Growth of Fingerlings.
From a start weight after weaning of about 1g, fish grow to an average of about 12-14g after three months. In our ponds, 28-64% of fish were less than 10g at three months. I suggest grading at this point. I will not predict what level you might have, with any luck it will be at the lower end.
With a starting average weight of about 15-20g after grading, another grade could be done after about 4 more months. By this time there should be a clear distinction between the non-performers and the racers. Our results had about 20% of these fish not performing (i.e. only 20-40g four months after grading).
Food For The Fish.
We have only found one supplier who reliably supplies a sinking pellet. Skretting has sinking barramundi and salmon diets. There is no difference in the crumbles.
Primo is importing a fish food, which has a low fat content and may be better for the fish. We have tried it and found that it floated.
Golden perch feed on the bottom for several hours after feeding. If possible, adjust circulation to retain pellets in raceway for as long as possible. In your water their feeding behaviour might be different.
Pellet size is dependent on the size of the fish. You may find that you need to use different sizes of pellet to those recommended here. Do not change over pellet sizes abruptly, as some fish choke to death on the larger pellets if you do. By monitoring left over feed you will see if certain size pellets are no longer being eaten.
Amount of Food.
We have found this relies on the quality of the food, but is quite variable. Food consumption will have to be monitored carefully and adjusted regularly.
In our experience, golden perch food consumption does not drop as temperatures drop. (Your temperatures being considerably lower may reduce food consumption).
*This is in ponds. Monitor feeding closely. We found that the midday feed stopped increasing after about two months and then fish stopped eating at midday. Likewise, after about 4 months the morning feed was less used and could be dropped.
Note: These average sizes are based on our removal of 50% of smaller fish in our ponds. As we had up to 64% of fish in the small size classes, some of our ‘large fish’ ponds have a substantial number of smaller fish in them, which pulls down the average.