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Following the classic lines of evidence of Hunter et al. (Hunter, J. R., Macewicz, B., Lo, N. C. H., and Kimbrell, A. 1992. Fecundity, spawning, and maturity of female Dover sole Microstomus pacificus, with an evaluation of assumptions and precision. Fishery Bulletin US, 90: 101–128.) on the fecundity type of fishes (determinate vs. indeterminate), the stock of horse mackerel (Trachurus trachurus) in Atlantic Iberian waters (ICES Division IXa) was shown to exhibit a mixed picture. Total fecundity, the total number of secondary growth (SG) oocytes dropped during the spawning season and there were reproductively active individuals with a distinct size hiatus between primary growth (PG) oocytes and SG oocytes, while no massive atresia was observed in late-season spawners. All of these characteristics matched with evidence for determinate fecundity. However, daily decrease rate of total fecundity was lower than daily specific fecundity (i.e. the number of eggs produced daily per unit weight) by orders of magnitude which suggested that the stock of SG oocytes was replenished during the spawning period through de novo oocyte recruitment. In addition, the maximum number of batches in reproductively active females was lower than the predicted annual number of spawnings, while total fecundity in recent spawners—those containing post-ovulatory follicles—was not lower than the fecundity of the remaining reproductively active females. All of these results suggest that, despite the aforementioned mixed lines of evidence, the fecundity of horse mackerel is clearly indeterminate. We attribute these mixed characteristics to the fact that, unlike most typical indeterminate spawners, horse mackerel ceases to recruit new SG oocytes during the latter part of its spawning season.

Cells of the parasitic, unicellular eukaryote Ichthyodinium chabelardi were isolated from eggs of sardine (Sardina pilchardus) and from a previously unrecognized host, bogue (Boops boops), off the Atlantic coast of Portugal. Immediately after release from the infected fish egg or newly hatched larva, I. chabelardi cells were spherical and non-motile. After few minutes, spherical cells became flagellated and motile. Following 2-3 days of incubation and several divisions, spherical flagellated cells developed a twisted elongate shape and moved vigorously. Sequences of the small-subunit ribosomal RNA gene (SSU rDNA) were identical for I. chabelardi of both hosts and so were sequences of ITS1, ITS2 and the 5.8S rRNA gene. This genetic similarity suggests that eggs of sardine and bogue were infected by one single population of I. chabelardi. The SSU rRNA gene sequence of I. chabelardi was, in turn, 97% similar to those of two identical Asian isolates of Ichthyodinium sp. Phylogenetic analyses showed high support for the inclusion of Ichthyodinium in the so-called Marine Alveolate Group I (MAGI). Two morphologically well-described genera, namely Ichthyodinium and Dubosquella, have now been shown to belong to this group of seemingly exclusively parasitic alveolates.