Ontogenetic variation of food intake and gut evacuation rate in larvae of the doncella Pseudoplatystoma punctifer, as measured using a non-destructive method Etienne Baras 1 , Grace V. Montalvan Naranjos 2,3 , Dustin V. Silva del Aguila 2 , Fred Chu Koo 2,4 , Re ´mi Dugue ´ 1,4 , Carlos Chavez 2,4 , Fabrice Duponchelle 1,3,4 , Jean-Franc ¸ois Renno 1,2,4 , C. Carmen Garcia-Da ´ vila 2,4 & Jesus Nun ˜ ez 1,3,4 1 IRD, UMR 226, ISE-M, Montpellier Cedex, France 2 IIAP-AQUAREC, Iquitos, Peru ´ 3 UNFV-FOPCA, Miraflores, Lima, Peru 4 LMI EDIA (Evolution et Domestication de l’Ichtyofaune Amazonienne), Iquitos, Peru Correspondence: E Baras, IRD, UMR 226, ISE-M, BP 5095, Rue Jean-Franc ¸ois Breton, 361, F-34196 Montpellier Cedex 05, France. E-mail: etienne.baras@ird.fr Abstract Food intake (FI) and gut evacuation (Rg) were mea- sured in larvae of Pseudoplatystoma punctifer (4.5– 18.4 mm SL) fed Artemia nauplii, taking advantage of the translucence of their abdominal region to achieve this in a non-destructive way, using digital photographs and mathematical reconstruction of gut volume content (ellipsoidal and cylindrical mod- els for stomach and intestine respectively). The inac- curacy of the method, with reference to counts of nauplii following fish dissection, was low (2.9 ± 1.5%) and independent of fish size (P = 0.6153). Pigmentation hampered measurement in fish >18– 19 mm SL. Anaesthesia was needed in fish >9.5 mm SL, thereby preventing the measurement of Rg in individual fish. The FI increased rapidly during the ontogeny, passing from <7% M at 0.6 mg, to 14% M at 1 mg and 21% M at 15– 40 mg, and then decreased slightly in larger fish. At 28.5°C, Rg (% M h 1 ) was modelled as Rg = 8.22 + 12.11 log FI + 6.30 log M – 12.67 (log M) 2 (R 2 = 0.904, d.f. = 27, with FI in% M and M in mg). Extrapolations of Rg over 24 h gave estimates of daily food rations that fit well with those mea- sured in cannibalistic P. punctifer. Keywords: food intake, gut evacuation, larva, catfish, Artemia, method Introduction The knowledge of how metabolism, growth and food consumption vary between fish species, devel- opmental intervals and environments is essential to understand their adaptive capacities and opti- mizing their culture. In particular, information on meal size and gut evacuation (Rg) rate is crucial for a correct adjustment of feeding levels and meal frequency (Elliott & Persson 1978; Jobling 1986; Canino & Bailey 1995), which are prerequisites to minimize size heterogeneity and cannibalism (Kubitza & Lovshin 1999; Baras & Jobling 2002). Several methods have been developed to measure the food intake (FI) of fish under controlled condi- tions (Jobling, Cove `s, Damsga ˚rd, Kristiansen, Kosk- ela, Petursdottir, Kadri & Gudmundsson 2001), with variable accuracy and success, depending on food type and fish size. In particular, numerous methodological restrictions concern fish larvae, which in addition to being small and delicate to handle, generally necessitate live prey (Rønnestad, Rojas-Garcı ´a, Tonheim & Conceic ¸a ˜o 2001). The removal method can be accurate for large prey (Baras, Hafsaridewi, Slembrouck, Priyadi, Moreau, Pouyaud & Legendre 2010), but is gener- ally less accurate for small prey, which can decay rapidly, be confused with faeces and pass unno- ticed (Kamler 1992), and so it is generally neces- © 2011 Blackwell Publishing Ltd 1 Aquaculture Research, 2011, 1–13 doi: 10.1111/j.1365-2109.2011.02982.x