No tanking: estimating the age of pelagic fish eggs directly from field samples

<p dir="ltr">This study establishes procedures which allow the daily egg production method (DEPM) to be applied to species for which descriptions of egg development stages have not been established and temperature egg development experiments have not been conducted. A method is described for staging pelagic fish eggs that can be applied to a wide range of species, negating the need for species-specific stage descriptions. The morphological characteristics used to distinguish stages are easily recognised in the laboratory and are present in the pelagic eggs of a large number of fish species. Individual stages are of similar duration and larval development through stages is approximately linear over time. Methods are also established for estimating spawning time and egg age directly from data obtained from ichthyoplankton surveys. A key benefit of this approach is that instead of assigning each egg stage a specified age for each temperature range based on model outputs from incubation studies, each individual cohort in each sample is assigned an age that aligns most closely with the age predicted for that cohort from the field data. The approach is simple, cost effective, and eliminates the potential for “tank effects” associated with laboratory-based incubation experiments</p>