Digestion of algae by Stegastes nigricans and Amphiprion akindynos (Pisces: Pomacentridae), with an evaluation of methods used in digestibility studies

Abstract

An investigation of the digestive physiology of two species of damselfish (family Pomacentridae) was undertaken, comparing a herbivore Stegastes nigricans with an omnivore/ planktivore Amphiprion akindynos. Apparent digestibility of Enteromorpha flexuosa (Chlorophyta) was calculated using both total collection and a range of ash‐marker methods. In addition, Van Soest's system of fibre analysis was used to determine the digestibility of algal cell walls. A comparison of total collection methods (comparing food intake v. faeces output) with ash‐marker methods showed that the calculated digestibility estimate will depend on the method used. Total dry matter digestibilities varied from 75 to 20% for S. nigricans and from 79 to 15% for A. akindynos. Comparable ranges were obtained for organic matter, cell wall, nitrogen and soluble carbohydrate. Digestibility estimates calculated using total collection methods were larger and less variable than estimates calculated using ash‐marker methods. Despite major methodological variation, there was no significant difference in the digestibility of algae between the two species.

Quality and digestibility of food ingested by various trophic fish groups in the Upper Paraná River floodplain

“…Protein digestibility of macrophytes (LFec) in this study was similar to that found in Najas guadalupensis for T. zilli (75.1%) by Buddington (1979) and for the algae Enteromorpha for S. nigricans by Galetto & Bellwood (1994).…”

“…Total diet ADCs, which recorded only plants (RIvi and Lfec), were lower than those found for cichlid Etroplus suratensis fed with Hydrilla verticellata (50-51.9%) by De Silva & Perera (1983), Tilapia nilotica fed with Cyanophyta (43%) by Moriarty & Moriarty (1973) and Stegaster nigricans fed with Enteromorpha algae (75%) by Galetto & Bellwood (1994). On the other hand, they were higher than those values reported by Buddington (1979) for T. zilli feeding on Najas guadalupensis (29.3%).…”

“…In this study, acid-insoluble ash was used as the internal marker, which according to Buddington (1980), Bowen (1981) Galetto & Bellwood (1994), Yossa &Araújo-Lima (1998) andvidal et al (2004), constitutes a good indicator in fish digestibility studies because it is not affected by the digestion process and is not assimilated.…”

Gut characteristics and assimilation efficiencies in two species of herbivorous damselfishes (Pomacentridae: Stegastes dorsopunicans and S. planifrons)

“…The assimilation efficiencies measured for both dusky and threespot damselfish fed artificial diets were higher than those reported for other pomacentrids feeding on algal foods (Lassuy 1984;Polunin 1988;Galetto and Bellwood 1994); this was clearly the result of an artificial diet formulated specifically for easy digestion. Nonetheless, on this diet threespot damselfish assimilated a larger fraction of the available protein than did dusky damselfish.…”

“…We collected feces from individual fish prior to feeding every morning ($0830 hours) and afternoon ($1530 hours) for five consecutive days (Edwards and Horn 1982;Galetto and Bellwood 1994;Sturm and Horn 1998). Destructive sampling of fish for intestinal contents would have interfered with retention time experiments, thus we are unable to assess any leaching of nutrients from fecal material; however both species were held, and samples were taken, under the same conditions.…”