Comparison of Three Methods for Estimating the Food Intake of a Fish

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Majkowski, Jacek, Hearn, William S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1984
• Subjects: Gadus morhua
• Online Access: http://dx.doi.org/10.1139/f84-024; http://www.nrcresearchpress.com/doi/pdf/10.1139/f84-024

Majkowski and Waiwood's (1981. Can. J. Fish. Aquat. Sci. 38: 1199–1206) method for evaluating the food intake of a fish involves numerically solving a first-order ordinary differential equation and using a minimization procedure. In this note, that method is compared with its two modifications created by (1) the elimination of a mathematical approximation ("improved method") (but this makes the food intake estimation computationally even more difficult), and (2) the introduction of a different mathematical approximation ("simplified method") to involve only simple algebraic calculations. As a result of the latter modification, a certain assumption in the original and improved methods is relaxed and the required experimental information is reduced. Growth and bioenergetic data concerning Gulf of St. Lawrence cod (Gadus morhua) are used to illustrate the three methods and to examine the validity of the mathematical approximations introduced. The use of the original method results in larger errors in food intake estimates for cod than the simplified method. The food intake estimates using the improved method differ considerably (by 3.6–23.5% and 1.7–10.4%, respectively) from those based on the original and simplified methods, if the corresponding ratio of the weight increment to the initial weight is large (>2.3).