WP1 focuses on a largely unknown aspect of pelagic fish production: allocation of energy to growth and reproduction; Strategies of energy allocation differ between the winter spawning species, like sardine, that capitalize energy in summer for subsequent reproduction in winter and summer spawning species that depend primarily on income energy during the spawning period to produce eggs (Somarakis et al. 2012). A detailed sampling is proposed that will follow the seasonal evolution and size-dependent changes in growth, egg production and somatic energy content in anchovy and sardine (Schismenou et al. 2012) and will provide new insights into energy allocation patterns. Knowledge acquired from this work-package is essential for the development of an egg production module in the fish bioenergetics models developed in WP2 as well as for their parameterization and validation.
The objective is to study seasonal patterns of growth, egg production and energy content in anchovy and sardine, i.e. how the surplus energy is allocated to growth and reproduction. This information is essential to properly parameterize the bioenergetics fish models in WP2 and it will allow the construction of a dynamic egg production algorithm for these models.
Description of work
Sampling of small pelagic fish will be carried out seasonally for one year to cover the reproductive and recruitment periods of both anchovy (summer spawner) and sardine (winter spawner). Fish will be collected onboard the commercial fishing fleet of the North Aegean Sea.
Task 1.1 Growth, condition and energy reserves (Month 1-16)
illustrate how the amount of energy allocated to growth and reproduction fluctuates seasonally, anchovy and sardine samples will be processed and the following parameters will be measured:
- Sex ratios; somatic and organ condition (condition factor, hepatosomatic and gonadosomatic index) and lipid content; for the latter it is essential to procure a fish fatmeter.
- Age and growth, through analysis of sagittal otoliths with image analysis techniques.
- Energy density.
Task 1.2 Egg production (Month 1-16)
To further investigate how fish size and the seasonal variations of energy reserves affect egg production, ovarian dynamics will be studied in detail:
- The numbers of oocytes per developmental stage will be estimated by applying advanced techniques and theories in reproductive biology of fish, i.e., the oocyte packing density theory, stereological techniques and the autodiametric method (Schismenou et al. 2012).
- Seasonal variations in egg size will be determined by measuring oocytes with image analysis techniques.
- Lengths-at-maturity will be calculated.
- Spawning frequency will be estimated using the post-ovulatory follicle method (Somarakis et al. 2012).
- Batch fecundity will be estimated from females in the stage of oocyte hydration or from oocyte size frequency distributions.
D1.1 Report on sampling design, field samples collected, laboratory analysis and preliminary results (Month 12)
D1.2 Manuscript on energy allocation to growth & reproduction in anchovy and sardine (Month 16)