The effect of fasting on nutritional status, organs size and isotopic composition in a Neotropical fish species (Jenynsia multidentata)

Abstract

Digestive flexibility is considered an adaptive response that allows individuals to minimise maintenance costs during periods of food scarcity. Here, we evaluated changes in body condition and digestive (and energy storage) organs size during short-term (7 days) fasting in Jenynsia multidentata. Also, we analysed changes in the isotopic composition and C:N ratio (a proxy of lipids content) in the intestine, liver and muscle. Fasted animals were compared against two feeding groups: field animals and animals fed ad libitum in the laboratory. We found that intestinal length was larger in feeding and field animals than in fasting fish, while intestine and liver masses were heavier in feeding animals, followed by field animals and then by fasting individuals. Liver and intestine δ15N was higher in fasting fish than in field animals, but δ13C did not differ between both groups. Finally, body condition, C:N ratios and perivisceral fat mass, were greater in feeding and field individuals than in fasting animals. This way, our results indicate that (i) changes in digestive and energy storage organs size during fasting in fish are ubiquitous and noticeable, and (ii) nutritional status of animals should be taken in account for a proper interpretation of stable isotope results, particularly for splanchnic tissues (such as intestine and liver).