Effect of dietary protein and lipid level on growth and metamorphosis of juvenile axolotl (Ambystoma velasci) reared under culture conditions

Abstract

Objective: To evaluate the influence of dietary protein and lipids levels in diets for survival, growth and metamorphosis of juvenile axolotls for its maintenance and conservation in captivity. Design/methodology/approach: Survival, growth, and metamorphosis were evaluated in two completely randomized trials, each lasting 90 days, using juvenile axolotls under laboratory conditions. In the first trial, growth and feed efficiency were evaluated using four isolipidic diets (12% lipid) with four protein levels (35, 40, 45, and 50%), and a commercial diet (manufacturer label: 46% crude protein; analyzed value: ~55%) as a control. In the second experiment, five isoproteic diets (40% protein) with five lipid levels (8, 10, 12, 14, and 16%) were used to assess their effects on growth and metamorphosis. Results: In the protein trial, growth was similar in all axolotls fed with the experimental diets, and significantly higher than the CT (P < 0.05). In the lipids trial, final weight (FW) and daily weight gain (DWG) of axolotls fed L16 were significantly higher (P < 0.05) than those of the other treatments, whereas the lowest growth was obtained with the lowest lipid level (L8); additionally, metamorphosis frequency increased as dietary lipid content increased, coinciding with a rise in ammonium concentration in the culture water. Limitations on study/implications: Despite originating from the same spawning, the individuals exhibited heterogeneous growth, thus limiting the availability of organisms per treatment. Furthermore, the species is characterized by facultative neoteny, which led to unexpected metamorphosis during the second study. Findings/conclusions: In conclusion, juvenile axolotls’ requirement of protein (%) is between 35–40% and 12–16% lipids to sustain efficient growth, whereas 16% lipids, together with environmental stressors such as elevated ammonium, may trigger metamorphosis.