Low pH inhibits salmonid egg hatching enzymes while brief hypoxia can promote and synchronize hatching.

Dear Tagried Kurwie,

You can try with pronase (Roche, Sigma, Merck,....). Test different concentrations and incubation times in order to find the optimal condition to induce larval hatch without compromising larval survival! Good luck!

Dear Tagried,

This mortality could be result from different reasons that could be divided as follows:

1) Broodstocks nutrition

2) Some infectious pathogen such as Saprolegnia pollution.

3) Genetic malformation

4) Environmental factors such as Hypoxia, temperature, pH,etc.

5) Toxic agents

You can consider all of them and try to find main mortality reason in your farm.

Regards

Be interesting to know the species and it's natural history. Is it a strict freshwater species or one where the eggs are washed downstream into a brackish or ocean environment. Water chemistry may be crucial to proper egg development and success.

When I used to sample streams for walleye eggs I noticed that the physical disturbance/vibrations from being collected and transported triggered well developed eggs to hatch. We also notice that hatch rates in the hatchery spike when a thunderstorm hits. I have no idea if this would help with your species, given all the other factors that others have mentioned.

Concerning to "Effect of Temperature and Size on Development, Mortality, and Survival Rates of the Pelagic Early Life History Stages of Marine Fish" you can see site as follows:

http://www.nrcresearchpress.com/doi/abs/10.1139/f91-065

Maybe it would be useful for you.

Eggs hatching in fishes like cyprinids may be induced and synchronized by lowering the water oxygen concentration. It is simple method, you can test it easily.

I agree with opinion of my dear friend Prof. Kasumyan.

As i mentioned before Hypoxia or decease of Dissolved Oxygen (DO) in hatchery water supply could be vital factor in survival rate of Early Life History Stages of Marine Fish.

thank you all for the valuable answers. I have ideas in mind which your thoughts confirmed them and will try them for this coming season. we used to use a paint brush connected to a drill to aid red fin perch eggs to hatch!!

to answer prof. Wooster question most members of the NZ Galaxiids spawn on the tidal river banks during spring tide and the hatching larvae wash down with the next spring tide to the ocean where they live for 2-3 months then migrate upstream

regards to all

Low pH inhibits salmonid egg hatching enzymes while brief hypoxia can promote and synchronize hatching.

Hi

I use pronase

Dear Tagried,

Hatching is induced by Physiological aspects (Hatching gland - Chorionase enzyme) and embryo motor activity. This may be induced by the environmental factors and, incubation period depends on the environmental factors such as oxygen, pH, temperature and salinity etc. You can check the reason easily with these factors.

Try zinc metalloproteases it has been found to dissolve the egg envelope in zebra fish

Hi Tagried. I agree with the most of comments. In general terms you can try with lowering of osmolarity, DO and/or pH; rising temperature; enzimes such as pronase, proteinase K or chorionase. It depends of your eggs and system, however it should be better to use that treatments as a short term (ca. 5-10 mins) stimuli since the larvae could be afected for that conditions if exposed directly. Let us know what worked in your case.

It might happen due to hardening of the egg chorion. I am not sure about your incubation system. You can use a short tannic bath (at very low concentration) before the incubation

I will try this as the eggs have some stickiness in them

thanks for the reply

I would recommend, as a more “fish friendly” solution, to test different environmental parameters (flow, temperature, light, aeration, etc) instead of chemical treatments, which are more likely to harm the embryo.

I agree with M. Chalaris, environmental parameters should be tested before using a chemical. It's simpler and cheaper.

I agree that environmental parameters are better and more practical especially for commercial scale production. I've used temp and salinity shock which worked to some extent and will try other methods such as reducing the pH because the adults of the spices live in an acidic environment. what chemical to use to lower the pH without harming the emerging larvae

As proposed by several people, did you try short egg emersion (about 20-30 seconds) ? Short hypoxia may accelerate hatching.

For pH lowering, you can use HCl. For pH = 6, the incubation water contain 1 µmol/L H+. Therefore, for example, for 900 mL of incubation water of pH>7, you should add 100 mL of a 10 µmol/L HCl solution (approx. 1 mL of 37% HCl + 1 L of water). Reminder: always put the acid into the water, and not the water into the acid because the reaction is highly exothermic. Always check the pH after preparation.

Hoping this helps.

thanks for the answer.