Models of temperature-dependent rate of development of pilchard Sardinops sagax eggs, to be used in routine procedures for estimating daily egg production

Abstract

Routine ageing of planktonic eggs requires mathematical models to describe the relationship between the time elapsed after spawning to reach a developmental stage and the ambient temperature of the water in which the eggs are developing. In this study, the temperature-dependent development time of II stages of pilchard Sardinops sagax eggs was determined for 10 temperatures between 12, 55 and 22, 05°C. The pilchard eggs were collected in late summer in the northern Benguela and incubated on board ship. Stages were not equal in duration, the earliest and latest stages being shorter than the intermediate stages at all temperatures. The duration of Stages VII and VIII deviated most with temperature, varying from 2 to 13 hours over the temperature range of the experiment. Two models, an exponential and a power function, were assessed to describe the development of the stages in relation to temperature. At lower temperatures, the power function fitted the observed data better than did the exponential function, and it was therefore chosen as the appropriate model for ageing pilchard eggs. These functions can now be used to construct automated procedures for ageing eggs, as a step in the estimation of daily egg production of pilchard. © 1995 Taylor & Francis Group, LLC.