Relationship between Body and Otolith Morphological Characteristics of Sabre Squirrelfish (Sargocentron spiniferum) from the Southern Red Sea: Difference between Right and Left Otoliths

Otolith morphology analysis is one of the main tools used for fish or fish stock identification. Moreover, otolith shape can also be used in animal dietary studies (stomach content) for the identification of prey fishes and their size according to the relationship between fish and otolith sizes. In the present study, the relationship between fish length and otolith morphological dimensions was investigated for the sabre squirrelfish, Sargocentron spiniferum (Forsskål, 1775) (family: Holocentridae). Samples of 185 fish were collected from the coast of the Red Sea, Egypt. To analyze the relationship between fish and otolith, otolith morphometric measurements (length, width, area, perimeter, weight, sulcus, and ostium) and shape factors (aspect ratio, compactness, form factor, rectangularity, roundness, ellipticity, squareness) describing the outline shape were extracted using image analysis. Generalized linear models were applied for the relationship between body length and each otolith morphology feature. From the relationships between the total length of fish and fourteen morphology features, only otolith length, caudal length, and squareness were significantly correlated with fish size. Our results provide more information for the relationship between fish length and otolith morphometric features.

Use of otolith morphology and morphometry for species discrimination of megrims Lepidorhombus spp. in the Central Eastern Adriatic Sea

Sagittal otolith morphology and otolith shape of two megrim species, Lepidorhombus boscii and Lepidorhombus whiffiagonis, were compared using descriptive morphological characters and Wavelet shape coefficients. Differences in otolith shape were examined by linear discriminant analysis (LDA). The first discriminant axis explained 66.6% of the variation between the groups, and the second axis 28.5%. Otolith classification based on LDA showed that in 79.5% of cases an otolith can be correctly classified based only on its shape. Relationships between otolith morphometric parameters (length and width) and fish size (total length) were described by fitting simple linear regression models. For L. boscii the highest positive correlation was found between right otolith width and total body length (R2 = 0.82), and for L. whiffiagonis between left otolith length and total body length (R2 = 0.39).

Relationship between Fish Length and Otolith Morphological Characteristics of Sargocentron spiniferum (Forsskål, 1775) from the Southern Red Sea

Otolith morphology analysis is one of the main tools used for fish or fish stock identification. Moreover, otolith shape can also be used in fish dietary studies (stomach content) for the identification of prey fishes and their size according to the relationship between fish and otolith sizes. In the present study, the relationship between fish length and otolith morphological dimensions was investigated for the sabre squirrelfish, Sargocentron spiniferum (Forsskål, 1775) (family: Holocentridae). Samples of 185 fish were collected from the coast of the Red Sea, Egypt. To analyze the relationship between fish and otolith, otolith morphometric measurements (length, width, area, perimeter, weight, sulcus, and ostium) and shape factors (aspect ratio, compactness, form factor, rectangularity, roundness, ellipticity, squareness) describing outline shape were extracted using image analysis. Generalized linear models were applied for the relationship between body length and each otolith morphology feature. From the relationships between the total length of fish and fourteen morphology features, only otolith length, caudal length, and squareness were significantly correlated with fish size. Our results provide more information for the relationship between fish length and otolith morphometric features.

Long-term temporal stability of Northeast Arctic cod (Gadus morhua) otolith morphology

Otolith shape analysis provides a robust tool for the discrimination of many fish stocks in the context of fisheries management. However, there has been little research to examine within-stock temporal stability of otolith morphology in relation to changes in the environment and stock conditions. This study investigated the variability of Northeast Arctic (NEA) cod (Gadus morhua) otolith shape between 1933 and 2015, using elliptical Fourier descriptors extracted from archived material of 2968 mature fish. Series of hierarchical multivariate models were developed to relate shape to the identified optimal windows of some environmental drivers. Differences between years accounted for <3% of the observed variation and no significant differences were found between the average cohort shapes. The models not only confirmed that fish growth was the strongest driver of shape differences, but also highlighted effects of temperature and biomass-related variables at different life stages. Extrinsic factors described only a small fraction of the observed variance, which indicates that environmental changes over time likely account for less than the natural inter-individual variability in otolith shape. These results suggest that overall shape remains relatively stable through time within NEA cod, which further contributes towards a consensus on the biological interpretation of shape differences.