The notion came from men of science, that determined long ago that mammal meat, and lipids, were not digested well by most of the commercial finfish they were feeding them to. As far as cost, some of those fats are now far less costly than oil from fish, cost is not a factor. In fact, typically commercial aquaculture has always taken the least costly path when designing food formulas. Plenty of lower cost, lower grade ingredients were used in the past .
(PDF) Review: Use of Animal Fats in Aquaculture Feeds (researchgate.net)
"Rendered animal fats are economical lipid sources that have been used in fish feeds for decades but their use
has been greatly limited for various reasons, such as poor digestibility and nutritive value,
and more recently, fear of disease transmission."
That was a paper written by a very well known aquatic feed researcher here in Canada, 20 yrs ago. There's plenty more where that came from - google is your friend for those interested.
From a previous post of mine here on MFK on this subject .......
Dr. Peter Burgess MSc, Ph.D.,of the Aquarium Advisory Service in England, is not only an experienced aquarium hobbyist, but also a scientist that specializes in the health & disease in fish. He has written over 300 articles and five books on fish health and is a visiting lecturer in Aquarium Sciences and Conservation at Plymouth University, where he works with the University of Plymouth training students in scientific research. Among his other positions, Dr. Burgess is a senior consultant to the Mars FishCare business and regularly runs fish health & husbandry courses for aquarists, fish scientists and vets. He's also a regular contributor & Fish Health consultant for the Practical Fishkeeping Magazine, as well as other magazines devoted to the fish keeping hobby.
Below is an excerpt from the Practical Fishkeeping Magazine and written by Dr. Burgess, titled;
Liver Damage and Red Meats
The routine of feeding beef heart and other red meats to Cichlids can ultimately give rise to health problems. Poultry meat is also suspect. Red meats, including lean meats such as beef heart, contain the wrong sorts of fats - these harden within the cold-blooded fish, leading to blockages and fatty deposits around the liver.
Also, the relative proportions of amino acids within the mammalian proteins are different to those required by fish. Hence, feeding red meats will cause the cichlid to excrete more nitrogenous (ammonia) wastes, thereby placing an extra burden on the biological filter."
The OP should have enough information to make an informed decision on how best to proceed.
Good luck
