A Laboratory Study of Particulate and Filter Feeding of the Northern Anchovy (Engraulis mordax)

Abstract

Observations of feeding behavior demonstrated that Engraulis mordax captures food by two distinctly different kinds of attack—biting and filtering. Artemia adults in high concentration evoke a biting attack and Artemia nauplii in high concentration evoke a filtering attack.Feeding trials with Artemia adults produced the equation w = 18.1 T^0.359 W^1.138, where w is weight of food consumed in milligrams, T is time in minutes, and W is fish weight in grams. Density had no effect over the range of 1–25 organisms per liter. Trials with adult Artemia also indicated that the maximum capacity of the digestive tract in milligrams is 93.3 W + 53.1.Feeding trials with Artemia nauplii produced the equation n = 6.31 T^0.970W^0.520 D^0.594, where n equals the number of nauplii consumed. Density (D) had a noticeable effect over the range 292–1120 organisms per liter. The volume of water filtered per minute was determined on the basis of this equation.The difference between the exponents for weight in the two kinds of feeding can be explained by the probability that when food is abundant filtering rate varies largely with area of mouth opening whereas particulate feeding rate varies largely with capacity.From the filtering rates determined in this study and estimates of filter food concentration in the sea it is hypothesized that E. mordax cannot obtain its daily nutritional requirement by indiscriminate filtering alone.