Settling velocity and total ammonia nitrogen leaching from commercial feed and faecal pellets of gilthead seabream (Sparus aurata L. 1758) and seabass (Dicentrarchus labrax L. 1758)

Abstract

The physico-chemical characteristics of particulate wastes of Sparus aurata and Dicentrarchus labrax were investigted. Changes in dimensions, settling velocity and total ammonia nitrogen (TAN) leached from commercial feed pellets was investigated after soaking. Also, the settling velocity and TAN leached from faecal pellets of these fish were assessed at 15 and 25ºC. The settling velocity of feed pellets was influenced positively by pellet weight and negatively by immersion length as a result of changes in pellet dimensions after soaking. The settling velocity of faecal pellets was determined by pellet weight. The experimental design did not allow identifying any consistent effect of water temperature on settling velocity. TAN leaching over time from feed and faecal pellets was successfully explained by means of a first order kinetic equation. For feed pellets, water temperature significantly affected the speed of the process and the time at which the maximum TAN leached was reached, but did not influence the maximum TAN leached. Leaching was related to feed pellet size, so the smaller the pellet, the higher the leaching. TAN leaching from faecal pellets was greater per unit weight than in feed pellets. However neither water temperature nor fish species influenced on TAN leaching from faeces.