The results in this study were no different than the vast majority of these studies, it lasted only 10 weeks, and targeted only certain species. The other literature cited did not all show the same results, I'm familar with a number of those papers and they all conclude different things based on different species, and even different forms of soy. Not all soybean has the same effect on fish, as an example soy isolate & soy concentrate are not only much higher in crude protein (approx 80%), they also do not contain the anti-nutitional matter that is sometimes found in regular soybean meal.
So first off none of these studies monitor the health of
any of these fish long term. These are ALL short term studies based on the growth & condition of commercially grown species that are grown out as fast as humanly possible, for as cheap as humanly possible, before they are sold for human consumption.
Even the commercial feed utilized as the control food in this study (a grow out trout chow from Skretting), at 50% protein & 18% lipid, could be very dangerous to many fish if fed to captive warm water tropical species. Foods with lipid levels in that range have been shown to have some very negative effects on various species of cichlids, including carnivorous species. (Ruth Francis-Floyd et al) Again, an epic failure if one was actually monitoring those same fish long term, on that diet.
Secondly, there can be different results from different species. In their study it was noted with regards to Red Snapper:
However, fish fed the high (soybean) replacement diets (36% and 48% SBM) had lipid deposits in the liver and low hematocrit levels, indicating a decline in fish health.
Oops, I guess you missed that part, which is exactly what I have already stated in this discussion.
Most of these feed studies in commercial studies last weeks, a few months if one is lucky, so the value of their data isn't always as impressive as it seems on the surface. The reality is that when fed these diets long term most tropical fish will not do well on foods that are high in terrestrial based plant matter, they simply aren't hard wired to assimilate those types of proteins, and those types of fatty acids. There are also studies that show severe liver damage caused from feeding some species of fish terrestrial based plant matter over an extended period of time due to the incorrect type of fatty acids found in those foodstuffs. This is especially true with marine fish.
This is also from that study;
Zhou et al. (2005) fed diets containing 0 to 60% SBM in increments of 10% to juvenile cobia, Rachycentron canadum. In terms of growth rate, up to 40% SBM was successful, but lipid levels in the liver, blood cell composition, and feed conversion ratio were negatively affected as SBM content increased. A replacement level of 18.9% was recommended.
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The study also said that omnivorous freshwater fish did much better on the diet. They could eat 100% SBM without side effects.
Actually, no they did NOT say that - and if anyone did, they would be talking out of their arse.
What they said was .......
Studies on freshwater species have generally shown higher maximum replacement levels of SBM for fishmeal. However; some of the freshwater species studied, such as catfish and tilapia, are herbivorous. Khan et al. (2003) were able to successfully replace 100% of the fish meal with SBM in the diets of Rohu, Labeo rohita.
Which I have already noted with regards to why species such as carp/koi will do much better on this pond diet, vs a cichla.
For anyone in interested further about what's actually found in this paper written by a graduate student, here is the correct link.
http://dl.uncw.edu/etd/2008-3/sullivank/katherinesullivan.pdf
Today there are numerous "least-cost" computer software programs designed to formulate commercial feeds, all geared towards a specific "human consumption" species of fish. Trout, salmon, catfish, tilapia, shrimp, etc. But none exist for any of the thousands of warm water tropical species that hobbyists keep in their tanks. Some of the info can be extrapolated, the rest is a bit of guessing game where one can only go by what they see in their tanks and their fish over years of use. But the bottom line is these cost saving methods for raw ingredients such as soybean meal, ground corn, wheat middlings etc, are only done to suit the commercial farmer, as in best growth for quick market sales - NOT the longevity of the fish, which is all I personally care about.
Manufacturers do not use these types of raw ingredients (soybeans, corn, middlings etc) because they are preferred over the quality and digestibility of other (more expensive) sources of raw ingredients - they use these types of ingredients to save production costs. Period!
The bottom line is many of these lower cost ingredients can have negative side effects, and cause negative health issues in fish, even in short term studies involving only "weeks" of feeding. The results thus far have proven to be species dependent, duration dependent, and inclusion rate dependent. And last but not least, ALL of these lower cost types of ingredients mentioned in studies such as this one (soybean meal, feather meal, poultry by product meal, meat/bone meal, and even fish meal) are all ingredient type & source dependent!
That is to say that not ALL soybean is created equally, anymore than ALL fish meal is created equally. This is where protein is NOT protein, as some people believe. Not even close. There are various grades of everything on the market, they all carry a different price tag, and they all can have different results when fed to a fish. This is quite common in feedstuffs, and is often why sometimes we can see such different results in different studies or papers utilizing the same apparent raw ingredients.
The beauty of all this is we as hobbyists can remove ALL of those potential problems, by simply feeding foods that do not contain large inclusion rates of terrestrial based plant matter, such as soybean meal, corn, low cost middlings, etc, and feed higher quality foods that have withstood the test of time, in millions of tanks around the world.
Or, we can argue until we are blue in the face how feeding a crap sandwich to our fish is somehow improving their lifestyle (and color?) while in our care.