I also wanted to revisit a previous comment. In the terrestrial vs aquatic plant matter discussion I posted the following, a quote from the study that the German group performed on Tanganyika, regarding gastrointestinal plasticity. It's not something just seen in various species of cichlids, or even fish, but also seen in reptiles, birds, and rodents.
"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in perch (Olsson et al. 2007), prickleback fish (German et al. 2006) and Tropheus (P. McIntyre and Y. Vadeboncoeur, unpublished data), and observations in Lake Malawi cichlids suggest shortening of the gut in mouthbrooding females that are unable to feed regularly (Reinthal 1989).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."
I understand that in nature many complicated and often misunderstood processes take place, and that we are always left somewhat guessing at a lot of how this will all play out in a glass box, IME, many of the species that were once considered specialized feeders (in nature) that required specialized diets (in captivity) has not played out to be true.
