Basis of an alternative method of utilizing low-resolution ovary-weight data for the assessment of seasonal spawning trends of the batch-spawning pilchardSardinops ocellatusin the northern Benguela system

Abstract

To cite this article: F. Le Clus (1989) Basis of an alternative method of utilizing low-resolution ovary-weight data for the assessment of seasonal spawning trends of the batch-spawning pilchard

Reproduction in Odontesthes bonariensis (Atherinidae: Pisces) from north-western Argentina

“…In many fishes the seasonal spawning cycle is partially determined from the GSI, which is relatively easy to interpret in species that spawn only once each year over a short period (Le Clus 1989). However, in multiple spawning fishes such as the silver fish which have an extended reproductive season (Calvo and Morriconi 1972), the onset of spawning, the peak and the end thereof are less easy to identify because these fish show a smaller magnitude of changes in the GSI.…”

Size-specific seasonal trends in spawning of pilchardSardinops ocellatusin the northern Benguela system, 1973/74

“…The average oocyte volume of the batch to be spawned was used as an index of the active-ripe stages of ovarian development of the batch-spawning pilchard (Le Clus 1989). Ovaries in which the average oocyte volume of the batch to be spawned was > 0,08 mm 3 were characterized as advanced.…”

“…The mean ovary weight at the commencement of hydration was used as the boundary above which the incidence of females with advanced ovaries was estimated. That mean ovary weight at the commencement of hydration and the associated standard length were calculated from the antilogarithm of the relationship between standard length (L), oocyte volume (V) and ovary weight (W) -Le Clus (1989) -where log w= 2,66 log L + 0,52 log V -1,97 . (1) The oocyte volume at the commencement of hydration (0,08 mm 3 ) was substituted into Equation I to give the lower boundary weight of advanced ovaries for the four length classes (Table II).…”

“…The incidence of ovaries close to spawning was estimated from size-differentiated ovary-weight data, taking boundaries for ovary weight established from the relationship between ovary weight, oocyte volume and fish length (Le Clus 1989).…”