For many reasons, for walleye larvae production, we need to increase light scattering effect in the tank water column. This is actually possible by adding suspended solids like clay, resulting in an increase in turbidity and therefore in light diffusion in the water column. However, this addition of clay causes some filtration problems in a recirculating system and it's why I'm looking for an alternative idea : dissolved matter like dyes? Mirrors setup? A kind of screen over the tank ? Special light diffuser?
Benjamin,
I work in the area of light propagation in turbid media. To mimic highly scattering biological tissues a common practice is to use soy oil bean emulsions. They are made commercially and are called Intralipid(c). You can buy it from Sigma-Aldrich Canada in ~100 mL(?) bottles (10%), cost ~$220 (check the site). This concetration (i.e., 10% concentration) produces really too much of scattering, so we dilute it by volume to get Intralipid-1%. It will look like skim milk. Perfect scattering, no problem for recirculation. Optical properties of Intralipid-1% were published in the article below:
https://www.researchgate.net/publication/228069709_Experimental_spectro-angular_mapping_of_light_distribution_in_turbid_media?ev=prf_pub
Contact me if you have have more questions about Intralipid.
Serge
Article Experimental spectro-angular mapping of light distribution i...
This is a very interesting approach. Intralipids could be the solution I need. Thank you very much, I will read about it.
We are actually testing the toxicity of TiO2 on walleye eggs at different concentration. I don't have the result yet, but at the turbidity needed, the concentration of TiO2 is very low. Further, I will test this compound on the biofilter.
I keep you in touch.
Also, the density of TiO2 is a bit high. Because I work on a low water flow, the sedimentation could be too fast.
I'd expect no toxicity from TiO2 but sedimentation may a problem indeed. I hoped that re-circulating water in the tank would re-suspend the particles but it may not work at a low flow...
Unfortunatly, TiO2 is not a solution because of the high level of sedimentation.
However, I'm thinking about a polarized screen sheet or freshwater microalgaes to produce turbidity. The turbidity needed is between 20 and 30 FTU (or NTU).
Because my eggs will hatch soon, I will use clay and postpone further tests to the next year.
I would be concerned about the possibility of lipid products interfering with swim bladder inflation in tank culture of walleye larvae. I think an algae product (live algae, algae paste, or even Spirulina powder) may be better - I have used these in flow through tank culture of walleye larvae to produce turbidity and normal spatial distribution of the fry (to keep them off the sides of the tank). I have also used algae products in marine larval fish culture. Algae products should not be a problem for recirculating culture systems.
Next year, microalgaes (alive) will be in my experimentation design. For the info, polarized screen didn't work.
It might be too late now but a semi tranparent cloth like Muslin cloth should scatter light.
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