The Use of Hepatic and Somatic Indices and Histological Information to Characterize the Reproductive Dynamics of Atlantic SardineSardina pilchardusfrom the Portuguese Coast

Abstract

Samples of Atlantic sardineSardina pilchardus (also known as European pilchard) were collected bimonthly from 2004 to 2008 off the central west coast of Portugal to describe the reproductive activity of this indeterminate batchspawning species; compare the seasonality of somatic growth, condition, and feeding; and evaluate differences between sexes. Monthly assessments of individual biological information for both males and females were complemented by histological analysis of ovaries during 1 year and liver tissues (both sexes) at different times of the reproductive cycle. The temporal patterns of the gonadosomatic index and various histological indices (most advanced oocyte stage, atresia incidence and prevalence, and spawning activity) indicated that Atlantic sardine were reproductively active mainly from October to March and that residual activity occurred in the remaining months. For both sexes, condition indices (hepatosomatic index, relative weight, and amount of fat stored) increased mainly during spring, reached a maximum at the end of summer just before the subsequent spawning season began, and then decreased during autumn and winter, declining to minimum levels at the beginning of spring coincident with a significant reduction in reproductive activity. Somatic growth took place mainly during spring and early summer for both sexes. The observed seasonal patterns in these biological properties suggest a seasonal transition from a period in which energy resources are allocated to reproduction (autumn and winter) to a period in which resources are allocated to growth and fat deposition (spring and summer). The only exception was the distinct hepatosomatic index pattern and the histological differences in hepatocytes between males and females during the spawning season, which may be related to the dual function of the liver in females (lipid metabolism and yolk precursor synthesis).Fish reproductive investment is the result of essential life history trade-offs in resource allocation (Stearns 1992). Energy that is surplus to the essential standard metabolic requirements (i.e., maintenance, locomotion, predation avoidance, and feeding activity) is allocated to somatic growth, energy storage, or reproduction after the fish reaches sexual maturation. The priority with which this surplus energy is allocated

Predicting the age of sardine juveniles (<em>Sardina pilchardus</em>) from otolith and fish morphometric characteristics

“…The distribution of birthdates of sardine juveniles sampled in this study is broadly consistent with the species spawning season in the Portuguese waters, which takes place from October to March, with a maximum between December and February (Coombs et al 2006, Nunes et al 2011 (Nunes et al 2011), successful births in summer might be explained by higher survival of early life stages due to improved female condition (Nunes et al 2011), higher temperatures and the onset of the upwelling season (Relvas et al 2009). Nevertheless, the above findings should be viewed with caution since our sampling was not designed for a quantitative estimation of the juveniles' birthdate distribution.…”

Are Portuguese coastal fisheries affected by river drainage?

“…Several pelagic fish species have their reproductive strategy adapted to coastal upwelling systems. They spawn in winter, when the northerly winds that cause upwelling are weaker, thus reducing the risk of Ekman transport offshore and ensuring inshore transport and larval retention (Nunes et al 2011;Stratoudakis et al 2007). The increase in productivity from summer upwelling will later benefit the feeding of the larvae (Santos et al 2001).…”

Bathymetric segregation of spawning stages in the Atlantic sardine Sardina pilchardus

“…The most important physiological mechanisms controlling buoyancy and bathymetric positioning in teleosts are somatic fat deposition, tissue-density control, and swimbladder dynamics (Brix et al 2009). Among these mechanisms, fat deposition should be excluded as a trigger of bathymetric segregation at spawning because fat cycling in sardines occurs on a seasonal basis (Nunes et al 2011a) while spawning cycling occurs several times within the breeding season (Nunes et al in 2011b). However, the remaining 2 mechanisms, i.e.…”