Frank, I already addressed the first question, that being when you add anything to a sheet sandwhich (typical farm feed pellet) the feed conversion ratio should improve. That's all that study found when duck weed was added. As far as protein, that would be based on dry weight, not wet weight, so first factor in 95% moisture content - then figure out your protein level. Almost nothing compared ot the protein in your pellet foods.
Duane, I totally agree with this; "And probably because of their diets low nutrient value, is one of the reasons for the constant eating.While carnivores such as dovii get away with every other day, or every 3 day feedings of high quality food, the above vegetarians have evolved to have a constant supply of this marginal food to be running thru their gut."
Having said that, science has proven that many of these cichlids, including those found in Lake Tanganyika, such as the various Tropheus sp, are very plastic when it comes to their gastrointestinal system, and their diet. I have posted about this in the past, including in my bloat sticky in the African folder.
http://monsterfishkeepers.com/forums/threads/bloat-causes-cures-and-big-myths.456034/
For decades Tropheus keepers felt that due to the intestinal length & long digestive process in that species, it should only be fed low protein "green" food, and that any amount of animal based protein could cause bloat. Yet science has proven that in captive bred species of Tropheus the intestinal length can be half of what's found in wild specimens.
A more recent study that was published in 2009 demonstrates just how great intestinal plasticity can be in response to the diet quality of various species of fish found in Lake Tanganyika.
Diet predicts intestine length in Lake Tanganyika’s
cichlid fishes
http://mcintyrelab.weebly.com/uploa..._functional-ecology-lt-cichlid-gut-length.pdf
"There is a striking inverse relationship between intestine length and algal nutrient content among populations of T. brichardi, suggesting substantial plasticity in response to food quality,
and thus a strong dietary influence on patterns of intraspecific variation.
Diet is a strong predictor of intestine length at both intra- and interspecific scales, indicating
that fish adjust their phenotype to balance nutritional needs against energetic costs. Furthermore, functional explanations for trophic diversification of cichlid fishes in the African Great Lakes have long focused on jaw structures, but our results indicate that intestinal plasticity in response to diet quality may also be an important mechanism for accommodating trophic shifts during evolutionary radiations.
Our use of nitrogen isotope data to
distill the complexity of tropical fish diets into a single axis
of trophic position provides the first quantitative evidence
that gut length varies in a continuous fashion as a function of
diet. These results suggest that intestine length in cichlids
reflects a trade-off between maximizing nutrient and energy
absorption and minimizing the energetic demands of digestive
tissues.
The nutrient content, energy content and digestibility of
food resources all influence the overall quality of an animal’s
diet. As these components of food quality are often correlated
(e.g. low-nutrient, low-energy, high-fibre plant material
vs. high-nutrient, high-energy, easily-digestible animal tissue),
their relative influences on intestine length are difficult
to separate.
Second, intestinal plasticity has been demonstrated experimentally in perch (Olsson et al. 2007), prickleback fish (German et al. 2006) and Tropheus (P.McIntyre
and Y. Vadeboncoeur, unpublished data), and observations in Lake Malawi cichlids suggest shortening of the gut in mouthbrooding females that are unable to feed regularly (Reinthal 1989). More generally, plasticity in internal organs in response to environmental stimuli has been documented in many vertebrates (reviewed in Piersma & Lindstrom 1997; Starck 1999), including fasting snakes (Starck & Beese 2002), migrating birds (Karasov et al. 2004) and rodents in fluctuating environments (Naya, Bozinovic & Karasov 2008), and the physiological mechanisms underlying gastrointestinal plasticity are well understood in several taxa (Starck 2003).
Thus, we believe that the observed variation in T. brichardi
intestine length is a largely plastic response to differences in
the nutrient content of their algal diet.
Both our broad phylogenetic survey and our intraspecific
comparisons suggest that the intestine length of Tanganyikan
cichlids is determined in large part by diet quality.
That paper clearly demonstrates just how adaptive wild Rift Lake cichlids can be when it comes to their diet. As long as one feeds a quality food, diet will generally be a non issue, and will not cause any type of major gastrointestinal stress. These fish were born to adapt. I do not believe that one could say the same thing about cattle, or Bison.
So moral of the story is if you want to feed fresh greens by all means do so, but from a nutritional standpoint if one is already feeding a quality dry diet, the gains from feeding foods such as duckweed will be minimal at best.
HTH
