Biología reproductiva de Diplodus sargus sargus en el golfo de Túnez (Mediterráneo)

The sexual activity of Diplodus sargus sargus in the Gulf of Tunis takes place from January to May. Spawning occurs in spring (March to May), as the water temperature rises from 15 to 18°C, just after the winter minimum. The spawning period increases as the latitude decreases. The overall male to female ratio was statistically different from unity. Size at sexual maturity (TL50) was 21 cm (4 years old). The length-weight relationship for all individuals was described by the following parameters: a = 0.015 and b = 3.051. D. s. sargus from the Gulf of Tunis is a rudimentary hermaphrodite with partial protandry.La actividad sexual de Diplodus sargus sargus del golfo de Túnez tiene lugar de enero a mayo. La puesta tiene lugar en primavera (marzo a mayo), cuando la temperatura del agua sube de 15 a 18°C, justo tras el mínimo invernal. A medida que la latitud decrece se observa un periodo reproductivo progresivamente más extenso. La relación machos/hembras fue significativamente distinta de uno. La talla de madurez sexual (TL50) fue 21 cm (4 años). La relación talla-peso para todos los individuos se describió por los siguientes parámetros: a = 0.015 y b = 3.051. D. s. sargus del golfo de Túnez es un a hermafrodita rudimentario con proterandría parcial.

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

Age, growth and mortality of the starry weever Trachinus radiatus Cuvier, 1829 in the Tunisian waters

Age, growth and mortality of the Starry weever Trachinus radiatus were studied for the first time from 214 individuals collected in the Gulf of Tunis between February 2014 and January 2016. The significant relationship between length-weight was observed for males (a = 0.011, b = 2.992, R2 = 0.981, n = 77) and females (a = 0.010, b = 3.036, R² =0.957, n = 109). Age was estimated by the observation of otoliths transverse thin sections. Age of individuals ranged from 1 to 15 years. The precision was measured by two age estimations from two experts and indicated a good agreement between them (PA = 85.6%, CV = 3.8% and IAPE = 4.1%). The growth parameters of the von Bertalanffy model were TL∞ = 38.41 cm, W∞ = 507.47 g, K = 0.3396 year-1, t0 = 0 year for males and TL∞ = 45.46 cm, W∞ = 914.04 g, K = 0.2136 year-1, t0 = 0 year for females. Age at first sexual maturity (tm) of T. radiatus was 3.5 years, while the age at optimum length (topt) was 6.6 years. The natural mortality (M), total mortality (Z), fishing mortality (F) and exploitation (E) rates were respectively M = 0.429 yr-1, Z = 0.453 yr-1, F = 0.024 yr-1 and E = 0.053.Age, croissance et mortalité de la vive à tête rayonnée Trachinus radiatus Cuvier, 1829 dans les eaux tunisiennes. L’âge, la croissance et la mortalité de la vive à tête rayonnée Trachinus radiatus Cuvier, 1829 ont été étudiés pour la première fois à partir de 214 individus échantillonnés dans le golfe de Tunis entre février 2014 et janvier 2016. Les coefficients a et b de la relation longueur total/poids ont été déterminés pour les mâles (a = 0,011, b = 2,992, R2 = 0,981, n = 77) et pour les femelles (a = 0,010, b = 3,036, R2 = 0,957, n = 109). L’estimation de l’âge a été réalisée à partir des coupes transversales d’otolithes. Les âges ainsi estimés étaient compris entre 1 et 15 ans. La précision de l’estimation de l’âge a été testée et les résultats montrent une bonne reproductibilité des estimations (PA = 85,6%, CV = 3,8% et IAPE = 4,1%). Les paramètres du modèle de croissance de Bertalanffy ont été estimés pour les mâles (L∞ = 38,41 cm, W∞ = 507,47 g, K = 0,3396 an-1, t0 = 0 an et pour les femelles (L∞ = 45,46 cm, W∞ = 914,04 g, K = 0,2136 an-1, t0 = 0 an. L’âge à la première maturité sexuelle (tm) de T. radiatus était de 3,5 ans, alors que l’âge à la taille optimum était de 6,6 ans. Les taux de la mortalité naturelle (M), la mortalité totale (Z), la mortalité par pêche (F) ainsi que l’exploitation (E) étaient respectivement M = 0,429 an-1, Z = 0,453 an-1, F = 0,024 an-1 et E = 0,053

Biometrical parameters and biological indices of the migratory species Conger conger (Linnaeus, 1758) from the northern coastal waters of Tunisia (Mediterranean Sea) / Paramètres biométriques et indices biologiques de l’espèce migratrice Conger conger (Linnaeus, 1758) des eaux côtières du nord de la Tunisie (mer Méditerranée)

The European conger eel Conger conger represents an important economic resource. Previous studies have provided some information about the biometry of C. conger. This paper presents the first research on biometrical parameters and biological indices of this species in Tunisia. Our sample includes 353 specimens, among them 66.57% females, 32.29% of undetermined sex and only 1.13% males. The length and weight of specimens ranged from 25.5 to 135 cm and from 17.26 to 5087 g, respectively. For the meristic characteristics, the number of pre-pectoral pores was 6, the total number of pre-anal pores ranged between 44 and 47 and the total number of vertebrae varied between 148 and 154. Five allometric relationships were examined. The comparisons of slope and intercept show differences between individuals of determined sex (males and females grouped) and those of undetermined sex. Analysis of the weight-length relationship showed a positive allometric growth. Our data provided the first investigation on the seasonal variation of three bio-physiological indices ; the condition factor does not show variations among seasons, the gonadosomatic index variation reinforces the hypothesis that sexual maturation of C. conger females occurs during the migration from coastal waters towards spawning areas in the deep sea and the hepatosomatic index was highest in spring for females. Since C. conger is widely distributed in the Mediterranean Sea and the Atlantic Ocean, our contribution allows useful comparisons and clarifies the morphological and bio-physiological aspects of this species.Le congre Conger conger représente une ressource économique importante. Des études antérieures ont fourni des informations sur la biométrie du Congre. Cet article présente les premières données sur les paramètres biométriques et les indices biologiques de cette espèce en Tunisie. Notre échantillon comprend 353 spécimens dont 66,57 % de femelles, 32,29 % de sexe indéterminé et seulement 1,13 % de mâles. La longueur et le poids des spécimens variaient respectivement de 25,5 à 135 cm et de 17,26 à 5 087 g. Pour les caractéristiques méristiques, le nombre de pores pré-pectoraux était de 6, le nombre total de pores pré-anaux variait entre 44 et 47 et le nombre total de vertèbres variait entre 148 et 154. Cinq relations allométriques ont été examinées, les comparaisons de pente et d’ordonnée à l’origine montrent des différences entre d’une part mâles et femelles groupés et d’autre part les individus de sexe indéterminé. L’analyse de la relation poids-longueur a montré une croissance allométrique positive. Nos données ont fourni les premières informations sur la variation saisonnière de trois indices bio-physiologiques ; le facteur de condition ne montre pas des variations significatives entre les saisons, la variation de l’indice gonadosomatique renforce l’hypothèse selon laquelle la maturation sexuelle des femelles se produit pendant la migration des eaux côtières vers les zones de frai et l’indice hépatosomatique était le plus élevé au printemps pour les femelles. C. conger est largement distribué dans la mer Méditerranée et l’océan Atlantique, aussi, nous avons contribué à travers cette étude à permettre des comparaisons utiles et à clarifier les aspects morphologiques et bio-physiologiques de cette espèce.Sallami Balkis, Ben Ibrahim Aymen, Ben Salem Mohamed, Chakroun-Marzouk Nadia. Biometrical parameters and biological indices of the migratory species Conger conger (Linnaeus, 1758) from the northern coastal waters of Tunisia (Mediterranean Sea) / Paramètres biométriques et indices biologiques de l’espèce migratrice Conger conger (Linnaeus, 1758) des eaux côtières du nord de la Tunisie (mer Méditerranée). In: Ecologia mediterranea, tome 46 n°1, 2020. pp. 5-15

Age, growth and mortality of the striped seabream Lithognathus mormyrus (Linnaeus, 1758) in the Gulf of Tunis (Central Mediterranean Sea)

Despite the high commercial value of the striped seabream Lithognathus mormyrus (Linnaeus, 1758) in the Gulf of Tunis, biological data on its age, growth and exploitation rate are lacking. With the aim of estimating growth parameters, 516 individuals, ranging from 6–27.5 cm total length and from 3.5–293.5 g total weight, were collected from the artisanal fishing fleet between February 2014 and July 2016. The somatic growth presented a positive allometry and was described by the equation TW = 6.54 10−3TL3.213. The monthly analysis of the marginal increment of the otoliths revealed that only one annulus was deposited per year. The estimated von Bertalanffy growth parameters were: L∞ = 30.18 cm, k = 0.303 year−1 and t0 = −1.42 years. Total and natural instantaneous rates of mortality were respectively Z = 0.784 year−1 and M = 0.698 year−1. Exploitation rate (E = 0.1) showed that the Gulf of Tunis stock of L. mormyrus is not overexploited. The estimated length class giving highest yield (Lopt) was 17.15 ± 1.71 cm

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