Otolith shape analysis is an efficient fish stock identification tool. However, most applications used left and right otoliths or only one of them arbitrarily chosen without testing for biases resulting from potential directional bilateral asymmetry (DA) in otolith shape, i.e. a unimodal population-level deviation form bilateral symmetry between right and left otolith shapes. In this study, 560 bogues (Boops boops) were sampled from 11 geographical locations from the Canary Islands to the Aegean Sea and elliptical Fourier descriptors were used to describe their otoliths’ shape. First, a significant otolith DA was observed at the global scale with an average amplitude of 2.77%. However, at the scale of sampling locations, DA was not always significant and varied in amplitude and direction. Second, population structure was investigated using the shape of either right otoliths or left otoliths or both together. Analyses based on right otoliths or both otoliths together, suggested three stock units: a North-Western Mediterranean Sea stock, an Eastern Mediterranean Sea stock, and a Central-Eastern Atlantic Ocean and South-Western Mediterranean Sea stock. In contrast, no coherent geographical pattern was found based on left otoliths. Our results highlight the importance of accounting for potential otolith DA in otolith shape-based stock identification.

A total of 455 Boops boops (Linnaeus, 1758) and 953 Trachurus trachurus Linnaeus, 1758 from the east coast of Algeria were examined for their parasitic Nematoda. Two hundred ninety-five specimens of larval stages L3 and L4 were collected from the peritoneal cavity of these two examined fishes. Photonic and scanning electronic microscopy (SEM) studies were performed on these larvae specimens in order to characterize their morphology. Two different species of Nematoda (Anisikidae) were identified: Anisakis simplex (Rudolphi, 1809) and Hysterothylacium aduncum (Rudolphi, 1802). These two parasitic species were reported for the first time on T. trachurus and B. boops from the eastern coast of Algeria. These parasites were attached on different organs in the abdominal cavity (particularly on ovaries and testes). The infestation rate changed according to the month and the host size. The parasitism did not show a significant negative impact on the condition of the examined fishes.

Otolith-shape analysis was examined to determine its utility for biological stock identification of the bogue Boops boops along the Algerian coast of the Mediterranean Sea. The outlines of 179 sagittal otolith pairs from fish collected at three locations (Oran, Bejaia and Annaba) between 2013 and 2016 were digitised and analysed for shape variation by elliptical Fourier analysis. Potential confounding sources of variation (fish length, age and sex, and left or right otolith position) were examined and accounted for in the analyses before interpretation of spatial differences in distribution of the stock. Redundancy analysis showed a significant difference between the left and right otoliths. No difference was correlated with sex and age, but fish length and sampling location had a significant effect on otolith shape. Differences in otolith shape between fish from the three locations (a span of approximately 1 000 km) were not large enough to support the concept of separate biological stocks of B. boops along the Algerian coast, as illustrated by the scatterplot of discriminant scores. This study emphasises the need to carefully evaluate the confounding effects of the otolith side (left or right) on the Fourier descriptors of otoliths before drawing conclusions about stock structure of the bogue on the basis of otolith-shape differences among samples of fish from different stocks or areas.

A study of the Algerian Branchiura, Argulus vittatus (Rafinesque-Schmaltz, 1814) was conducted using the scanning electron microscopy (SEM). New morphological features are reported for the first time (mouth con, first maxilla, second maxilla, structures and ornamentation of thoracic segments, structure of semen papillae, etc.). The morphology of small and large female specimens was compared. Two new hosts, Pagellus erythrinus L. and Sparus aurata L., are reported for this species. Until now, six host species were reported for A. vittatus, and stenoxenic specificity for Sparid fishes was observed for Algerian specimens. The biogeographical distribution of this species seems to be restricted to the eastern coast of Algeria. Additional information about the host specificity, ecology, and life cycle of this parasitic species were given.

The otolith, found in both inner ears of bony fish, has mainly been used to estimate fish age. Another application that has been developing significantly in recent years, however, is the use of otolith shape as a tool for stock identification. Often, studies have directly used the shape asymmetry between the right and left otoliths. We tested the magnitude of directional asymmetry between the sagittal otoliths (left vs. right) of 2991 individuals according to their catch locations, and we selected species to evaluate whether directional asymmetry may itself be a tool to evaluate stock boundaries. Elliptical Fourier descriptors were used to describe the otolith shape. We used a flatfish, the common sole (Solea solea, n = 2431), from the eastern English Channel and the southern North Sea as well as a roundfish, the bogue (Boops boops, n = 560), from the Mediterranean Sea. Both species showed significant levels of directional asymmetry between the testing locations. The bogue otoliths showed significant asymmetry for only 5 out of 11 locations, with substantial separation between two large areas: the Algerian coast and the western part of the Italian coast. The sole otoliths showed significant asymmetry in the shape analysis (3.84%–6.57%), suggesting a substantial separation between two large areas: the English and French parts of the English Channel and the southern North Sea. Consequently, directional bilateral asymmetry in otolith shape is a potential new method for stock identification.

The family Blenniidae inhabiting freshwater systems has been scarcely studied, particularly in North Africa. The present study focused on the biology of Salaria fluviatilis (Asso, 1801) from Kabylie region (northern Algeria). A total of 198 specimens were sampled from May 2015 to May 2016. The total length of this fish varied between 4.9 and 12.7 cm and its total weight varied between 1.2 and 23.7 g. The age of this fish species varied between 1 and 3 years. The sex ratio of S. fluviatilis was in balance (SR = 0.98). The results of our investigation of length-weight relationship show highly significant correlation (p > 0.001); the correlation coefficient r varied between 0.966 and 0.985. The specimens of this fish species exhibited positive allometry in males (b = 3.195) and negative allometry in females (b = 2.782). Growth parameters were higher in males than in females, except for the growth rate (K) where the values were close. The growth performance index (Φ) was similar in both sexes, which confirms the same growth potential for males and females. In Kabylie region, the breeding period of S. fluviatilis occurred between April and July. Our results of analysis of the hepatosomatic index (HSI) and Fulton’s K show that liver energy reserves are not devoted for reproduction; however, muscle reserves seem to support this physiological activity. In perspective, more biological studies must be carried out on this rare and poorly studied fish.