No abstract

The alpha taxonomy of the globally distributed shark genus Squalus has been under intense investigation recently, and many new species have been described over the last decade. However, taxonomic uncertainty remains about several taxa. Without consistent nomenclature and the ability to reliably distinguish between the different Squalus species, basic data collection, downstream conservation and management efforts are seriously compromised. To aid in clarifying the taxonomic status of Squalus species in the eastern Atlantic and Mediterranean, we assessed species diversity at the molecular level and evaluated the consistency in species identification in the region. Samples from all nominal Squalus species recognized in the above regions were collected in an international effort and sequenced for regions of the mitochondrial COI and ND2 genes. These data were further analysed alongside publicly available sequences, including 19 of the 26 Squalus species globally recognized, to compare the regional genus‐level diversity with that found elsewhere. Our results confirm inconsistent species identification in the eastern Atlantic and Mediterranean Squalus, particularly concerning S. blainville and S. megalops, and reinforce the need to revise the status of S. megalops and S. mitsukurii as they may include several distinct species distributed around the world. The status of S. blainville is also discussed in the light of the current findings and its problematic taxonomic history.

-Otolith shape analyses were conducted on three different species of Mullidae (Mullus barbatus barbatus, M. b. ponticus and M. surmuletus). The otolith shape was described by 19 harmonics from elliptic Fourier descriptors. In a first step, their comparison through canonical discriminant analyses (CDA) was run for all fish with right otoliths, left otoliths and both otoliths pooled. The latter possibility had a higher discriminating power and allowed much more visually explicit results. This implied that the two otoliths were not similar as often claimed, and had each their specific information. In a second step, the CDA demonstrated strong spatial discrimination of local populations from various areas within the Mediterranean basin, i.e. NW Mediterranean, Aegean Sea and Black Sea, and between sites within each area. The percentage of well classified individuals of M. barbatus in predefined groups varied between 78 to 100% depending on sites, and even reached 100% for each site for M. surmuletus. These spatial patterns were most likely linked to differences in environmental conditions between areas and sites, such as effects of strong river runoffs and differences in depths and/or habitat types. In a third step, CDA also evidenced ontogenetic discriminations of mullet populations that could be linked (i) to influence of diet of fish of various sizes and (ii) to changes in physiological conditions according to the stage of development of the fish.

A miniature fiberoptic endoscope was used to observe the processes of particle encounter and retention inside the buccopharyngeal cavity of suspension-feeding tilapia. Small particles (38 µm to 1.0 mm in diameter) were trapped in strands and aggregates of mucus, which usually slid posteriorly on the ceratobranchials of arches I­IV towards the esophagus while the fish pumped water through the buccopharyngeal cavity. During stage 1 of periodic reversals of water flow inside the buccopharynx, mucus-bound particles usually lifted off the arch surfaces and travelled a short distance in an anterior or anterodorsal direction. During stage 2 of a reversal, the mucus usually resumed travel in a posterior or posteroventral direction and exited the field of view. Mucus was present less often during feeding on large particles (3­10 mm in diameter) than on small particles, and large particles were rarely observed to be attached to mucus. We discuss the advantages to suspension-feeding fishes of using aerosol filtration by mucus entrapment rather than sieving, and predict that many cichlid and cyprinid suspension feeders that consume bacteria and phytoplankton use mucus for aerosol filtration.