Edad y crecimiento de Spondyliosoma cantharus (Sparidae) en el Golfo de Túnez

Age and the growth of the black seabream Spondyliosoma cantharus (Linnaeus, 1758) from the Gulf of Tunis were investigated using scales and otoliths. The length-weight relationship showed that the growth rates were isometric for females whereas males and the whole sample present a positive allometry. The monthly evolution in marginal increment data of scales and otoliths revealed that only one annulus is formed per year in April. Fish length and radii of the scales or otoliths were closely correlated. The von Bertalanffy growth equation was fitted on mean back-calculated length-at-age data, resulting in the parameter values L∞=35.4 cm, k=0.15 y–1 and t0=–0.19 y for scales and L∞=38.6 cm, k=0.10 y–1 and t0=–0.14 y for otoliths. Parameters estimated from scale and otoliths were significantly similar. However, taking into consideration the lower standard deviations of means for estimates based on otolith readings and the higher variance explained by the regression line fitted to otoliths, the latter seem to be more appropriate for ageing S. cantharus. The maximum age of the black seabream of the Gulf of Tunis is 10 years. Large discrepancies in growth parameters between geographic areas are the result of different growth patterns.Se han investigado la edad y el crecimiento de la cántara Spondyliosoma cantharus (Linnaeus, 1758) del Golfo de Túnez a partir de la lectura de las escamas y los otolitos. La relación talla-peso revela que las tasas de crecimiento son isométricas en las hembras, mientras que los machos y en toda la muestra existe una alometría positiva. La evolución mensual de los incrementos marginales de las escamas y los otolitos muestra que se forma un solo anillo anual en abril. La correlación entre la longitud de los peces y el radio de las escamas o los otolitos es muy elevada. La ecuación de crecimiento de von Bertalanffy se ha ajustado a la media talla-edad retrocalculada resultando en los siguientes valores para los parámetros de las escamas (L∞=35.4 cm, k=0.15 año–1, t0=–0.19 año) y los otolitos (L∞=38.6 cm, k=0.10 año–1, t0=–0.14 año). Los parámetros estimados a partir de las escamas y los otolitos resultaron significativamente similares. Sin embargo, teniendo en cuenta que las desviaciones estándar de las medias en las estimas son más bajas, y que la varianza explicada es mayor en la regresión ajustada a los otolitos, la lectura de los otolitos parece ser la más apropiada para datar la edad de S. cantharus. La edad máxima de la cántara del Golfo de Túnez es de 10 años. Las grandes diferencias en los parámetros de crecimiento entre áreas geográficas se deben a diferentes pautas de crecimiento

Length - Weight relationship and condition factor of Phycis phycis (Linnaeus, 1766) and Phycis blennoides (Brünnich, 1768) [Actinopterygii, Gadiform, Phycidae] in the Gulf of Tunis

In our study length-weight relationship are presented for 213 Phycis phycis and 270 Phycis blennoides caught between September 2007 and August 2008 and collected from trawler fishing in the Gulf of Tunis. The length-weight relationships and the condition factor were computed separately for sexes and for different seasons. The parameters of the length-weight relationship for the population as a whole are all well correlated (r²> 0.92, p 0.05) between seasons for P.phycis. However, it differs significantly (p 0.92, p 0,05) pour P. phycis alors qu'elle présente une allométrie majorante chez P. blennoides. L’étude des variations saisonnières de la relation taille-masse indique que la croissance est isométrique chez P. phycis quelque soit la saison. Chez P. blennoides, pendant les saisons estivale, automnale et hivernale, la croissance est isométrique ; cependant au printemps la croissance présente une allométrie majorante (t > 1,96 ; p > 0,05). Le facteur de condition calculé en fonction des sexes et des mois confirme bien ces constations

Growth and age estimation of the greater forkbeard, Phycis blennoides (Actinopterygii: Gadiformes: Phycidae), from the Gulf of Tunis (central Mediterranean)

Background. The greater forkbeard, Phycis blennoides (Brünnich, 1768), is a gadiform species, which has economical value and its population is dwelling in a 60–800 m depth range throughout the Atlantic and the Mediterranean. Along African north coast, there is a lack of information about the biology (age, growth, sex-ratio) of this species. This study provides the first data on population parameters of P. blennoides in Tunisia. Materials and Methods. Specimens of Phycis blennoides were collected from the landings of the artisanal fisheries between September 2007 and June 2010. The length–weight relations were determined according to the allometric equation: W = aTLb. Growth parameters were estimated using the von Bertalanffy growth equation. Results. Length (TL)–Weight (W) relations were allometrically positive for the females (W = 22.10–4TL3.409), males (W = 13.10–4TL3.674), and both sexes (W = 19.10–4TL3.460), without significant differences between males and females. The relation between otolith weight and age showed a significant difference between males and females. The growth parameters were calculated as TL∞ = 57.17 cm, K = 0.193 · year–1, t0 = –1.578 · year for the females, and 44.74 cm, 0.313 · year–1, and –1.210 · year for the males, respectively. The females grew faster than the males which did not exceed 45 cm. The growth performance index Ф' calculated for the females (2.80 cm· year –1) and males (2.79 cm· year –1) yielded similar results. Conclusion. Results reported in this work will contribute to the knowledge on the biology of P. blennoides in Tunisia, with the aim of generating sufficient information to improve future stock management and sustainable fisheries

Age, growth and mortality of Sciaena umbra (Sciaenidae) in the Gulf of Tunis

The growth and mortality of the brown meagre, Sciaena umbra from the Gulf of Tunis, were investigated using a sample of 276 specimens, ranging from 15.3 to 49.2 cm total length and from 43 to 1565 g total weight. Specimens were collected from artisanal fisheries between October 2008 and September 2011. Otoliths were extracted, thin cross-sections were realized and radii were measured. The log-linear morphometric relationships between total length-total weight and total length-otolith radius were significant (p < 0.05), showed positive allometry (b=3.15) and isometry (b=0.90), respectively. The marginal analysis suggested that only one growth increment was deposited per year. The maximum age of the brown meagre was 22 years for males and 31 years for females. The fit of the von Bertalanffy growth function was significantly different between sexes (p <0.05): TL∞=43.8 cm, k=0.145 y–1, t0=–4.88 y for males and TL∞=50.1 cm, k=0.105 y–1, t0=–5.71 y for females. The instantaneous total (Z) and natural (M) mortalities were estimated for each sex, resulting in an exploitation ratio (E=F/Z) of 0.43 for males and 0.46 for females.Se investigo el crecimiento y la mortalidad de Sciaena umbra del golfo de Tunez, utilizando una muestra de doscientos setenta y seis especimenes que miden de 15.3 cm a 49.2 cm de longitud total y pesan de 43 g a 1565 g. Las muestras se recogieron de pesquerias artesanales entre octubre de 2008 y septiembre de 2011. Se extrajeron los otolitos, se realizaron secciones transversales delgadas y se midieron los radios. Las relaciones morfometricas logaritmicas entre la longitud total y el peso total de una parte y la longitud total y el radio de otolito de otra parte resultaron significativas (p<0.05) y mostraron respectivamente alometria positiva (b=3.15) e isometria (b=0.90). El analisis marginal sugirio que se depositaba un solo anillo de crecimiento por ano. La edad maxima de la corvina negra es de 22 anos para los machos y de 31 anos para las hembras. El ajuste de la funcion de crecimiento de von Bertalanffy resulto significativamente diferente entre los sexos (p<0.05): TL‡=43.8 cm, k=0.145 y.1, t0=-4.88 y para los machos y TL‡=50.1 cm, k=0.105 y.1, t0=.5.71 y para las hembras. La mortalidad instantanea total (Z) y natural (M) se estimo para cada sexo, dando como resultado una tasa de explotacion (E=F/Z) de 0.43 para los machos y de 0.46 para las hembras

Otolith growth and age estimation of bastard grunt, Pomadasys incisus (Actinopterygii: Perciformes: Haemulidae), in the Gulf of Tunis (Central Mediterranean).

Background. Bastard grunt, Pomadasys incisus (Bowdich, 1825), is reported as a well-established species in the Mediterranean Sea. Although bastard grunt has rapidly expanded its area of distribution in the Mediterranean, there is no information about its age and growth. The aim of this study was to provide data about growth, condition, and first sexual maturity of the species in order to contribute to a better management of its fishery. Materials and methods. A total of 515 specimens of bastard grunt were caught in the Gulf of Tunis. The age was determined from otoliths. Length–weight relation, von Bertalanffy equation, and growth rate were employed to evaluate the fish growth. Also the condition factor and length at first sexual maturity were calculated. Results. In the Gulf of Tunis population, females were significantly predominant and the overall sex ratio (M : F) reached the value of 1 : 2.17. The two sexes showed a positive allometric growth. The marginal increment analysis validated the annual deposition of one single annulus in the winter. Growth in (total) length (TL) was approximately 65% during the first year of life. The von Bertalanffy growth equation was TL = 23.9 × (1 – e–0.186 × (t + 4.62)). The somatic condition of fish increased markedly during the late spring and summer. Length at first sexual maturity of the bastard grunt was 16.6 cm for males and 16.8 cm for females, which correspond to an age of about 2 years. Conclusion. The rapid growth during the first year of life, the early maturity and the moderately short life cycle contribute to the relatively fast spreading of the species