Populations of four species of juvenile fish- Rhabdosargus sarba, Acanthopagrus australis, Achoerodus
viridis and Girella tricuspidata-were sampled from a seagrass bed in Botany Bay, New South Wales.
Fish were collected eight times between 22 March 1990 and 22 February 1991, using a small seine-net.
Growth rates were calculated from the progression of cohorts in length-frequency distributions.
Cohorts of R. sarba, A. australis and A. viridis grew most slowly during winter (0.02, 0.04 and
0.21 mm day-1, respectively); growth then increased, peaking just prior to the loss of the cohort from
the habitat (0.3 1, 0.24 and 0.39 mm day-1). Populations of R. sarba, A. australis and A. viridis were
comprised of one or two cohorts that remained in the habitat for at least 3-4 months. Conversely, up
to seven cohorts of G. tricuspidata were found between October and February, and most cohorts did
not remain in the habitat for more than 2 months. As a result, there were only two confident estimates
of growth for G. tricuspidata: 0.23 mm day-1 between October and November, and 0.34 mm day-1
between January and February. Individuals of each species were also kept in a flow-through 4000-L
tank of sea water. Growth of cohorts of fish kept in the tank was very similar to that found in natural
populations during the same time period. The rates of recruitment and loss of cohorts from seagrass
can be rapid and these factors must be considered in designing a sampling programme to assess growth
by analysis of length-frequency distributions.
REARING OF JUVENILE DONKEY-EAR ABALONE (Haliotis asinina) IN FLOW-THROUGH TANKS WITH THE ADDITION OF DIFFERENT SUBSTRATES
