Recent publications demonstrate arginine sparing potential of guanidinoacetic acid

I think the issues are much more complex than any of these papers suggest. You may be interested in papers by Marissa Chamruspollert. I think her dissertation is available on line. Below is a little AI summary I just got through Google. The rather small "plateau" before toxicity from GAA is particularly interesting in that similar responses have been seen from nutrients involved in methyl metabolism. DS MicKittrick observed something similar for choline and methionine (before B12 supplements) and we saw it from folic acid.

The Core Research Findings

Chamruspollert, Pesti, and colleagues established foundational rules for how poultry process arginine:
• The Arginine-Methionine-Creatine Pathway: Unlike mammals, chickens cannot synthesize arginine on their own because they lack a fully functional urea cycle, making it an absolute dietary requirement. The researchers demonstrated that the relationship between arginine and methionine is closely tied to the biosynthesis of creatine (which provides energy to skeletal muscles).
• Arginine Toxicity & Alleviation: They confirmed that if a diet has excess arginine but is low in methionine, the chicks suffer from a significant growth depression. This occurs because the overabundance of arginine drives up the demand for methyl groups to create creatine, which rapidly strips the body of methionine. This "toxicity" or growth depression can be easily mitigated by supplementing extra methionine back into the diet.
• The Three-Way Amino Acid Interaction: Their papers (such as those published in Poultry Science and British Poultry Science) showed a complex three-way interaction among arginine, methionine, and lysine. High levels of dietary lysine can aggravate arginine issues by competing for the exact same cellular transport mechanisms.
• Impact of Heat Stress: They also mapped out how ambient temperatures affect these pathways. When chickens are raised in hot temperatures (around 35°C / 95°F), the rate at which arginine is metabolized through arginase or converted into creatine slows down drastically.

Could you please explain—with full scientific clarity and a few examples—the concept of sparing cysteine ??and arginine in aquaculture and poultry feeds? This could significantly help expand the market for GuanAMINO!.

Anyone wanting to understand the nutrition of methionine and related compounds could start with a book by Vincent duVigneaud. It is a wonderful read for anyone interested in how biochemistry and nutritional sciences developed together and anyone wanting to understand sulfur and methyl nutrition. After you have studied it, the Chamruspollert dissertation will make more sense. There are plenty of examples in both.
https://www.abebooks.com/first-edition/Trail-Research-DuVigneaud-Vincent-Cornell-University/30654091737/bd. You may be able to get a copy through many libraries. The book was based on a series of lectures given at Cornell in the 1950's after duVigneaud won the Nobel Prize in chemistry for his work. One thing I have noticed missing from many discussions of methionine metabolism is an alternative pathway of methionine degradation through methyl thio propreinate. I think that work has mainly been done in rats and people. You could start by looking at work in NJ Benevenga's laboratory for the rat work and I'm sure it cites others. I know little about fish nutrition. You will find out from duVigneaud's book that some shellfish contain a compound called dimethylthetin, which also acts as a methyl donor for some reactions. After you have studied these, it will be nice to discuss more specifics. Good luck.