Abstract
SUMMARY: Diet analysis of larval fish may clarify the role that zooplankton—not only its abundance but also its size structure and taxonomic composition—may have on larval growth and subsequent recruitment levels. Taking into account the increase in size during larval stages, we followed a larval size-dependent approach for the analysis of prey size in the diet of larval sardine (Sardina pilchardus). Studies on feeding patterns of clupeid larvae typically involve a problem due to regurgitation and defecation of gut contents during capture. Therefore, an alternative sampling method was tested in this study, but no significant differences from conventional methods were found. Despite the low feeding incidence observed (23%), we found a circadian feeding pattern with the highest mean gut contents after dawn, decreasing during the day and with the lowest values at night. Diet was mostly composed of copepod developmental stages, mainly nauplii, and prey size increased with larval size following a power function. Maximum and mean prey size were related to larval mouth gape, though other factors may be restricting the maximum prey size ingested, since most prey width values were between 20 and 40% of larval mandible width.
Highlights
Food availability is considered to be one of the main factors affecting the growth rate of pelagic fish larvae (Hjort, 1914)
The objective of our study was to analyse some characteristics of Sardina pilchardus larval diet in the Cantabrian Sea, namely to determine circadian feeding patterns, number of prey in the gut and feeding incidence, and type and size of consumed prey, taking into account the increase in size during the larval period
We considered station (S) and sampling time (T) as independent factors for the general linear modelling (GLM) analysis, taking four levels for S and five levels for T since sampling times were different for each S
Summary
Food availability is considered to be one of the main factors affecting the growth rate of pelagic fish larvae (Hjort, 1914). The match/mismatch hypothesis (Cushing, 1975) argues that recruitment variability in pelagic fish populations is caused by massive mortality of larval stages under low food availability conditions. Houde (1987) demonstrated that small changes in growth and mortality rates may. GONZÁLEZ-QUIRÓS cause high variability in the magnitude of recruitment. Precise characterisation of larval diet is needed in order to understand which particular food availability conditions may cause growth variability
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