Abstract Aeolosomatidae are cosmopolitan meiofaunal Annelida characterised by small size and almost exclusively asexual reproduction. This study is the first report on the chromosome morphology of ...two aeolosomatid species. Giemsa staining and propidium iodide labelling were performed. The somatic chromosome number of Aeolosoma viride was 2n=30 with many biarmed elements, whereas A. hemprichi showed 60 small chromosomes with a dot-like appearance. Asexual reproduction, with its clonal transmission of chromosomal repatternings, probably ensures the fixation of new karyotypes in species of Aeolosoma .
Agametic reproductive activity (via paratomy) of Aeolosoma viride was analyzed throughout the life cycle in individually reared specimens. Aeolosoma viride is organized in linear chains of 3–4 ...zooids; the main zooid is anterior, and the secondary zooids are positioned posterior to the main zooid in inverse order with respect to their degree of growth, the most advanced being at the posterior end, and those less advanced nearer the main zooid. On average, worms lived 66±10 d and produced 57±6 offspring. A budding area located in the sub-terminal part of the main zooid produced chaetigers that formed the origin of the secondary zooids. A growth zone was located in the posterior end of each secondary zooids. Fission occurred between the penultimate and the last zooid of the chain. Just before fission, the growth zone of each secondary zooid became a budding area. Agametic reproduction was via multiple paratomy with linear succession of the secondary zooid and terminal fission. The structure of the chain was therefore modulated by the interaction of the processes of budding, growth, cephalic differentiation, and fission, which occurred continuously and on different timescales. Values of parameters describing paratomic activity (interval between origin of the zooids, time to produce a chaetiger, growth time of the zooids, and interval between the fission of the filial chains) are low early in an individual's life, but increase during senescence. Due to its relatively rapid lifecycle and high reproductive activity, A. viride is a convenient experimental organism for the study of agametic reproduction.
Abstract
Fishery discard survival depends on multiple conditions; caution is essential when survival study outputs are employed to support management decisions. The study presents a stepwise ...procedure, devised to estimate discard survival, that accounts for the variability characterizing commercial fishing practices. The procedure was applied to the first survival study performed onboard rapido trawlers targeting Solea solea in the Mediterranean Sea. Undersized specimens collected during sorting were assessed for vitality; some were retained for captive observation. The main drivers affecting discard survival at the time of catch sorting (immediate survival) were identified and used to outline four different operational conditions set (scenarios). Immediate survival in each scenario was subsequently modified by applying a hazard coefficient of survival after 5 days of captive observation in relation to each vitality class, thus obtaining relative survival estimates following discarding. Temperature and air exposure duration were found to exert a major effect on survival, with catch weight and seabed type being additional important factors. The relative survival rate showed an aggregate value of 22.9% (10.5–33.4%). Scenario approach can enhance our understanding of the stressors influencing discard survival. The outcomes are discussed to explore the potential applications of the procedure to the identification of mitigation strategies.
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