Thanks. I will give a shot and see
Anything that meets their nutritional needs and contains carotenoids like Astaxanthin should help them color up (it's a bit hidden the quotes below, but Spirulina helps with coloration too):
Yes, it has been demonstrated on a number of different fish both internally (like salmon) and externally (such as red tilapia* and other species listed in the block quote below), a few different inverts, and even flamingos.** It seems to primarily be a reddening agent (though it has been shown to have some other positive effects too), yes.
"Astaxanthin has been shown to promote growth and skin pigmentation in flame-red dwarf gourami Trichogaster lalius (Baron et al., 2008), blood parrotfish Cichlasoma synspilum × C. citrinellum (Li et al., 2018), green swordtail Xiphophorus helleri (Putra et al., 2020), discus fish Symphysodon (Song et al., 2017), rainbow kurumoifish Melanotaenia parva (Meilisza et al., 2018), and red swamp crayfish Procambarus clarkii (Cheng and Wu, 2019)."***
A similar effect has been noted for other colors with things like Spirulina (different carotenoids involved though).****
*Source:
**Source:
Effects of dietary astaxanthin enrichment on enhancing the colour and growth of red tilapia, Oreochromis sp.
The aim of this research was to examine the effects of dietary inclusion of astaxanthin from Haematococcus pluvialis in commercial fish feed on the co…www.sciencedirect.com
***Source:
****Sources:
Effect of dietary astaxanthin on growth, body color, biochemical parameters and transcriptome profiling of juvenile blood parrotfish (Vieja melanurus ♀ × Amphilophus citrinellus ♂)
To investigate the effects of dietary astaxanthin on fish growth and body color, blood parrotfish juveniles were assigned to three groups: control (CL…
