You're right, I misunderstood your initial comment, so I see that my response was completely antithetical to your thoughts on nutrition. Sorry for the miscommunication!
Please note a few of the companies (italicized) are very young, so their websites don't have much info.
I recommend this site for keeping up with which companies are active in the alternative proteins space: https://newprotein.org/. For cultured meat, click "Alternative Protein V 3.0" and it's in the top left (or just head to page 2 for a more zoomed in view).
While I definitely understand your concern, I also think we can see this as a fascinating opportunity to improve the nutritional value of meat. These muscle cells in culture will generally speaking continue to produce the proteins, ECM components, etc. that they normally do, but we can also take advantage of genetic manipulation, metabolic engineering, and nutrition engineering to make them achieve more. A paper came out last year (https://www.sciencedirect.com/science/article/pii/S109671762...) in which mammalian cells (bovine primary and immortalized murine muscle cells) were modified to produce plant proteins without loss of phenotype. From the abstract:
"... to endogenously produce the antioxidant carotenoids phytoene, lycopene and β-carotene. These phytonutrients offer general nutritive value and protective effects against diseases associated with red and processed meat consumption, and so offer a promising proof-of-concept for nutritional engineering in cultured meat."
It may also be worth mentioning that cultured meat offers other potential gains in the arena of human health -- no need for antibiotics in a sterile manufacturing setting (so not contributing to antibiotic resistance), vanishingly low risk of foodborne illnesses and novel viruses like covid-19, etc..
I don't know about WildType specifically, but it's not necessarily true that a salmon would need to die at any point in the process. Cells from a simple muscle biopsy could be cultured for this purpose, and a single biopsy may have the potential to produce a great deal of cells depending on the culture conditions. Or they may have developed an immortalized salmon cell line from an initial biopsy that they can proliferate indefinitely (though this leads to questions about genetic drift after a certain number of population doublings; I'm sure they would have a bunch of frozen vials to restart from early passage numbers every few batches though).
I'm not an expert on WildType's specific process, but I've read that while mammalian cells need to be grown at ~37 C 5% CO2, fish cells can be grown at lower temps due to differences in biology. I just read a paper where salmon cells were incubated at 13 C and 3% CO2. Could be that they're expecting energy cost savings with no need to pre-warm media, heat bioreactor, etc., but it's also possible that cooling will be necessary (depending on the location of the plant) or that mammalian metabolism will produce enough heat that bioreactor heating may not be an issue. I think the jury is still out on that. So maybe they just looked at where they could find their niche in a market with lots of pork, beef, and poultry companies already? Or maybe the founders really cared about marine ecosystems?
I've got good news for you! The Shojinmeat Project's (https://shojinmeat.com/wordpress/en/) mission is the "democratization of cellular agriculture." They develop methods for DIY cultured meat (recently someone posted about developing a cell culture medium out of Red Bull). They do have a slack channel, but it's not super active recently. They're pretty active on Twitter though, and their website is a great resource. I would highly encourage you to also check out some of Yuki Hanyu's (founder) talks on YouTube; he's great.