Ana L. Ibáñez

Does compensatory growth modify fish scale shape

Although the shape of fish scales is useful for determining stock membership, the role of extrinsic (e.g. habitat, food type) and intrinsic (e.g. growth) factors in determining variation in fish scales shape has not been determined. This study examined whether fish scale shape changes as a result of compensatory growth in juveniles of the cyprinid roach, Rutilus rutilus (L.) reared on a fish farm in the UK. This was analyzed using geometric morphometric methods. Sufficient evidence was generated to accept the assumption that food availability and type between different growing-out facilities resulted in compensatory growth and this was sufficient to cause scale shape differences. This was tested using multivariate analysis of variance (MANOVA) analysis with the principal components scores of specimens (PCs) as dependent variables, to investigate whether fish scale shape (where the configuration of landmark coordinates were scaled, translated and rotated) form (where the configuration of landmark coordinates were translated and rotated not scaled) and allometry free (allometrically adjusting scale shape according to length) are related to holding facility (as fixed factor). Cross validated discriminant analysis was used to assess and compare the efficacy of shape, form and allometry free information. Identification rates are much better than chance with allometry free and shape alone, and classification is improved when size is taken into account.

Comparative morphometrics and relative growth of Cherax quadricarinatus (Von Martens, 1868) males and females

The relative growth of Cherax quadricarinatus (Von Martens, 1868) males and females under laboratory conditions was analysed using eight somatic measurements. The allometry of each measurement was estimated in relation to total length. The morphometrics were analysed using the original values, as well as normalized data from each group. Two multivariate analyses were carried out: reciprocal averaging and principal components. The results showed that the two sexes have a similar relative growth. However, differences between the sexes were recorded with respect to shape, though not to size. This was observed through the reciprocal averaging analysis after normalization of the individuals in each group. The morphometric variables that differentiated the sexes were the width and length of the chela, followed by the length of the abdomen. Thus, this analysis was useful to determine the shape differences between the sexes in culture.

Scale deformity descriptions for 23 species of fish, from various geographical areas and habitats

A renewed interest in fish scale anomalies prompted the present study, wherein we document a wide range of scale morphological abnormalities, including deformities in shape and structure, of a large number of species. In the present study, 63 cases of deformities were reported from 23 fish species collected from five countries. The abnormalities observed are discussed within the framework of contaminated aquatic environments, with a goal of recognising the cause of abnormality. Deformed scales exhibited different shapes, showing both slight (n=52 cases) and severe (n=9 cases) abnormalities. The scale deformations described in the present study should help direct future work on the relationships between environmental condition and fish health.

Can the name Mugil cephalus (Pisces: Mugilidae) be used for the species occurring in the north western Atlantic?

Menezes et al. (2010) show that Mugil cephalus Linnaeus, 1758 is different from Mugil liza Valenciennes 1836, the latter being the mullet found along the Atlantic coast of South America. They also suggest that individuals identified as M. cephalus from the northwest Atlantic could represent a population of M. liza in this region, since they doubt the presence of M. cephalus in waters colder than the ones of the West Indies. In order to clarify the presence of M. cephalus in the northwest Atlantic, this study compares meristic and morphometric measurements of M. cephalus and M. liza from the Gulf of Mexico with those obtained by Menezes et al. (2010) for M. liza from South America and for M. cephalus in the Mediterranean Sea. Results show that there are differences in both morphometric and meristic data between the two species. The morphometric measure that differentiates these species is the distance from the snout to the dorsal fin, which is positioned backwards in M. liza compared with M. cephalus. The body width is consistently greater in M. cephalus than M. liza. The meristic character that discriminates between both species is the number of scales in the longitudinal series that, in M. cephalus, ranges from 38 to 43 while in M. liza between 32 to 39. The information presented in this work confirms the presence of M. cephalus in the Gulf of Mexico and the sympatric presence of M. liza is established, even if its abundance is quite low.