Advances in methods for determining fecundity: application of the new methods to some marine fishes

Estimation of individual egg production (realized fecundity) is a key step either to understand the stock and recruit relationship or to carry out fisheries-independent assessment of spawning stock biomass using egg production methods. Many fish are highly fecund and their ovaries may weigh over a kilogram; therefore the work time can be consuming and require large quantities of toxic fixative. Recently it has been shown for Atlantic cod (Gadus morhua) that image analysis can automate fecundity determination using a power equation that links follicles per gram ovary to the mean vitellogenic follicular diameter (the autodiametric method). In this article we demonstrate the precision of the autodiametric method applied to a range of species with different spawning strategies during maturation and spawning. A new method using a solid displacement pipette to remove quantitative fecundity samples (25, 50, 100, and 200 milligram [mg]) is evaluated, as are the underlying assumptions to effectively fix and subsample the ovary. Finally, we demonstrate the interpretation of dispersed formaldehyde-fixed ovarian samples (whole mounts) to assess the presence of atretic and postovulatory follicles to replace labor intensive histology. These results can be used to estimate down regulation (production of atretic follicles) of fecundity during maturation

Advances in methods for determining fecundity: application of the new methods to some marine fishes

17 pages, 9 figures, 6 tables.Estimation of individual egg production (realized fecundity) is a key step either to understand the stock and recruit relationship or to carry out fisheries-independent assessment of spawning stock biomass using egg production methods. Many f ish are highly fecund and their ovaries may weigh over a kilogram; therefore the work time can be consuming and require large quantities of toxic fixative. Recently it has been shown for Atlantic cod (Gadus morhua) that image analysis can automate fecundity determination using a power equation that links follicles per gram ovary to the mean vitellogenic follicular diameter (the autodiametric method). In this article we demonstrate the precision of the autodiametric method applied to a range of species with different spawning strategies during maturation and spawning. A new method using a solid displacement pipette to remove quantitative fecundity samples (25, 50, 100, and 200 milligram [mg]) is evaluated, as are the underlying assumptions to effectively fix and subsample the ovary. Finally, we demonstrate the interpretation of dispersed formaldehyde-fixed ovarian samples (whole mounts) to assess the presence of atretic and postovulatory follicles to replace labor intensive histology. These results can be used to estimate down regulation (production of atretic follicles) of fecundity during maturation.T his study was jointly funded under Eu ropean Union Frame Work V Q5RS -2002 - 01825 and the Institutes in England (Department of the Environment, Food, and Rural Affairs), Norway (Institute of Marine Research), and Spain (Consejo Superior de Investigaciones Científ icas, and A ZTI Tecnalia (publication number 424))Peer reviewe

Horse mackerel fecundity in relation to lipid content

During the 2004 mackerel and horse mackerel triennial egg survey fecundity of horse mackerel (Trachurus trachurus L.) was estimated using a new gravimetric and image analysis system. The fecundity estimates and mean oocyte diameters showed great variation between and within different institutes. Horse mackerel fecundity increased during the spawning season and showed no decline at the end of the spawning season. This indicates that this species is likely to be an indeterminate spawner. The lipid content was estimated from whole horse mackerel collected during the three months prior and during the spawning season. Lipid content rapidly decreased during the period of ovary development prior to the onset of spawning, but remained rather constant during spawning. A relationship between fecundity and lipid content could not be found. A time series of lipid content estimates collected annually or triennially might provide an index for changes in fecundity over time. Sampling needs to be carried out prior to the onset of spawning, when fat content is at its highest. Annual stomach content estimates collected in successive years might provide an index for food availability and feeding success. The stomach analysis carried out in 2004 indicated that horse mackerel was feeding only at a low level during the spawning perio

Reproductive output traits of the simultaneous hermaphrodite <I>Serranus scriba</I> in the western Mediterranean

We studied multiple individual parameters that affect the reproductive output in the painted comber Serranus scriba, a simultaneous hermaphroditic fish that is widely exploited by recreational fishing in temperate marine coastal regions. Batch fecundity was significantly affected by maternal size, but was not related to maternal age or condition. However, egg quality as estimated by egg dry weight was significantly influenced by the interaction effect of maternal size and age. An empirical assessment demonstrated the existence of a diel spawning pattern based on a daily release of a partial fraction of eggs related to sunset time. Buoyancy varied during the incubation period, but it consistently resulted in positive buoyancy that situated the eggs near the top of the water column. This study represents the first estimation of reproductive output of the simultaneous hermaphrodites S. scriba and also provides a comprehensive study about the potential maternal factors that affect egg production. These results are a crucial step towards ongoing efforts to improve the stock assessment of this species.Peer Reviewe

Identifying spawning events in the Japanese flounder Paralichthys olivaceus from depth time-series data

Vertical swimming events (VSEs) of the Japanese flounder, Paralichthys olivaceus, recorded by high-frequency depth data loggers, were analysed to identify spawning events. In total 25,907 VSEs from 10 adult fish were classified into 4 clusters using a k-means method. VSEs in a specific cluster (cluster-S) characterised by accelerated vertical swimming were identified as possible spawning events. Both the descent (0.43 ± 0.22 body length s− 1) and ascent rates (0.43 ± 0.24 body length s− 1) of VSEs in cluster-S were more than 4 times faster than in any other VSE. Our analyses indicated that 4 individuals exhibited the spawning events during the recording periods. The estimated spawning frequency ranged from 0.74 to 0.90 events day− 1. These values were comparable to those obtained in other field and laboratory studies. The spawning condition of fish at the time of recapture was confirmed by separate histological and anatomical observations, which supported the cluster analysis results. These results suggest that a clustering technique can be successfully applied to identify spawning behaviour from time-depth data of free-swimming flatfishes that exhibit vertical swimming movements