Sex-related growth differences in the sagittae of Prionotus nudigula Ginsburg, 1950 (Pisces: Triglidae)

The objetive of the present paper is to study the morphology of the sagittaand calculate the morphometric parameters of the otolith in relationship to growth in length and weight of the fish. These parameters are necessary in age and growth studies of Prionotus nudigula Ginsburg 1950.For each one of the 354 Prionotus nudigula specimens sex, total weight (P) and height (LT) were recorded, as well as maximum length (LO) and maximum width (AO) of the sagittae. The following relationships were analysed: P vs LT, LO vs LT, AO vs LT, LO vs P and AO vs LO for female and males, as well as without discriminution between sexes. For the study of these relationships, the regression model with potential adjustment roas used.The right and left sagittae of the same individual did not present meaningful differences; therefore, they are morphometrically and morphologically equal. The otoliths of males and female did not present differences in the topography of the internal and external side.y, though is was observed that the sagittae of females are longer than those of males.The analysis of relationships P vs LT and LO vs LT and P show that at the same length, females are heavier than males. The relationships LO vs LT and P and AO vs LO indicated a differential growth between sexes.El objetivo de este trabajo es el estudio de la morfología de la sagitta y el cálculo de los parámetros morfométricos del otolito en relación al crecimiento en longitud y peso del pez. Dichos parámetros son necesarios en estudios de edad y crecimiento de Prionotus nudigula Ginsburg 1950.De cada uno de los de 354 ejemplares de Prionotus nudigula estudiados se registraron sexo, peso total (P) y talla (LT), midiéndose asimismo la longitud máxima (LO) y la anchura máxima (AO) de las sagittae. Se analizaron las relaciones entre: P y LT, LO y LT, AO y LT, LO y P, AO y P, AO y LO tanto para hembras y machos como sin discriminación entre sexos. Para el estudio de dichas relaciones se empleó el modelo de regresión con ajuste potencial.Las sagittae derecha e izquierda de un mismo individuo no presentaron diferencias significativas, por tanto son morfométrica y morfológicamente igual. Los otolitos de machos y hembras no presentaron diferencias en la topografía de las caras interna y externa, aunque se observó que las sagittae de las hembras son más largas que las de los machos.El análisis de las relaciones entre P y LT y de LO con LT y P muestran, para una misma talla, que las hembras son más pesadas que los machos. Las relaciones entre LO y LT y de P y AO con LO permitieron observar un crecimiento diferencial entre sexos.Instituto Español de Oceanografí

¿El otolito de pejerrey (Odontesthes bonariensis), refleja el estrés ambiental?

It has been proven that otoliths reflect morphology, morphometry and chemical composition of the environment that fish frequent. However, it has not been established if extreme environmental changes can be reflected by such structure. In this study, we analyze the morphology and morphometry of otolith sagitta of silverside (Odontesthes bonariensis) living in a setting that shows important environmental changes as Chasicó lake in Buenos Aires province (38°37.380’S- 63°4.735’W). We compared physicochemical parameters of water (pH, conductivity, ion concentration Ca2+, Mg2+ y Cl-) measured in the lake in 2010 with bibliographic data of 1999, 2003 and 2004 and different morphometric variables of silverside otoliths captured in 1998 and in 2010. The ion concentration of Ca2+, Mg2+ y Cl- increased between 11% and 90% in the period 1999-2010; the lake reduced its surface 20% in conjunction with a decrease in precipitations. We observed alterations in the distinctive morphological otolith pattern in about 18% of the individuals sampled, like irregular edges and perforations. We found a smaller width-length relation of the otolith for the year 2010 thus, indicating a decrease in its circularity. These morphological variations could be provoked by alterations in calcium carbonate deposition related to an increase in salinity and conductivity due to reduction in the surface of the lake. In conclusion, this study would indicate that morphology and morphometry of otoliths reflect environmental stress.Instituto de Limnología "Raúl A. Ringuelet

¿El otolito de pejerrey (Odontesthes bonariensis), refleja el estrés ambiental?

It has been proven that otoliths reflect morphology, morphometry and chemical composition of the environment that fish frequent. However, it has not been established if extreme environmental changes can be reflected by such structure. In this study, we analyze the morphology and morphometry of otolith sagitta of silverside (Odontesthes bonariensis) living in a setting that shows important environmental changes as Chasicó lake in Buenos Aires province (38°37.380’S- 63°4.735’W). We compared physicochemical parameters of water (pH, conductivity, ion concentration Ca2+, Mg2+ y Cl-) measured in the lake in 2010 with bibliographic data of 1999, 2003 and 2004 and different morphometric variables of silverside otoliths captured in 1998 and in 2010. The ion concentration of Ca2+, Mg2+ y Cl- increased between 11% and 90% in the period 1999-2010; the lake reduced its surface 20% in conjunction with a decrease in precipitations. We observed alterations in the distinctive morphological otolith pattern in about 18% of the individuals sampled, like irregular edges and perforations. We found a smaller width-length relation of the otolith for the year 2010 thus, indicating a decrease in its circularity. These morphological variations could be provoked by alterations in calcium carbonate deposition related to an increase in salinity and conductivity due to reduction in the surface of the lake. In conclusion, this study would indicate that morphology and morphometry of otoliths reflect environmental stress.Instituto de Limnología "Raúl A. Ringuelet

Trophic niche partitioning of five skate species of genus Bathyraja in northern and central Patagonia, Argentina

Overexploitation of marine communities can lead to modifications in the structure of the food web and can force organisms like elasmobranchs to change their feeding habits. To evaluate the impact that fisheries have on food webs and on the interactions between species, it is necessary to describe and quantify the diet of the species involved and follow it through time. This study compares the diet of five skate species using the data obtained from the by-catch of the Argentine hake (Merluccius hubbsi) fishery in north and central Patagonia, Argentina. Diet composition was assessed by analysing the digestive tract contents and trophic overlapping between species of the genus Bathyraja: Bathyraja albomaculata, Bathyraja brachyurops, Bathyraja macloviana, Bathyraja magellanica and Bathyraja multispinis. A total of 184 stomachs were analysed. The diets of B. albomaculata and B. macloviana mainly comprised annelids, whereas that of B. brachyurops primarily comprised fish, including hake heads discarded by the fishery. The diets of B. magellanica and B. multispinis were largely based on crustaceans. Despite the morphological similarities and their shared preference for benthic habitats, no complete diet overlaps were found between the different species. These results suggest that these skate species have undergone a process of diet specialisation. This is a common feeding strategy that occurs to successfully eliminate competition when resources are limited, which corresponds to the conditions found in an environment being affected by the pressures of overfishing.Fil: Tschopp, Ayelen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Cristiani, Franco. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales y Ciencias de la Salud - Sede Puerto Madryn. Departamento de Biología y Ambiente; ArgentinaFil: Garcia, Nestor Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Crespo, Enrique Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales y Ciencias de la Salud - Sede Puerto Madryn. Departamento de Biología y Ambiente; ArgentinaFil: Coscarella, Mariano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales y Ciencias de la Salud - Sede Puerto Madryn. Departamento de Biología y Ambiente; Argentin

Otolith and vertebral morphology of marine atherinid species (Atheriniformes, Atherinopsidae) coexisting in the southwestern Atlantic Ocean

Studies on marine ecosystems rely on the identification of fish prey species of piscivores (fish, aquatic mammals, and aquatic birds) based on their bones and otoliths. The stomach contents of piscivores show predation on marine atherinids of commercial value; however, their identification is difficult due to the coexistence of these species. The objective of the present study is to propose the use of hard structures (otolith, caudal vertebrae) as a tool for the identification of marine atherinid fishes occurring in the southwestern Atlantic Ocean. Sagittae (200 pairs) were removed from the otic capsules for further examination and measurement. The vertebral column of individuals from each species was also removed for examination. The morphological pattern of the sagitta otoliths of five marine species belonging to the genus Odontesthes was consistent with that of the subfamily Atherinopsinae, with these patterns being species specific. In Odontesthes argentinensis, O. platensis, and O. smitti, the caudal vertebrae present an expansion of the haemal arch walls forming a haemal funnel with distinctive morphology, while this characteristic is absent in O. incisa and O. nigricans. The hard structures used in this study proved to be a useful tool for the correct identification of the atherinids found in the diet of piscivorous species from the southwestern Atlantic Ocean. A key based on the major morphological features of sagittae and hemal arches is provided.