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The growth and nutritional condition of Engraulis anchoita larvae in the Argentine-Uruguayan Common Fishing Zone (AUCFZ) were determined. The condition was estimated considering the standardized RNA/DNA ratio (RDs) of the muscle trunk. Growth was studied calculating an instantaneous growth rate on the basis of a model that includes RDs and temperature. Otoliths growth was also calculated measuring the thickness of the last three fully formed daily increments. Samples were collected in March 2014. The 12 oblique tows performed with a Bongo net 300 μm mesh size showed presence of larvae in 6 of them. They were separated on board and fixed in liquid nitrogen. Afterwards, they were measured, heads dissected with a scalpel and muscle trunks individually lyophilized (N = 128). Two oceanographic sections located on the southern margin and northern margin of the AUCFZ (COSTAL I and II, respectively) were compared. The RDs ratio of larvae evidenced a good nutritional condition. No significant differences in the larval condition or growth between both sections were found. A positive correlation between the RDs index and size was observed; thus, comparisons were made considering the larval developmental stage. The RDs for pre-flexion larvae in COSTAL I was 2.53 ± 1.29 (n = 53) and 2.92 ± 1.22 (n = 7) in COSTAL II. For larvae in flexion it was 3.41 ± 1.07 (n = 22) and 2.91 ± 0.86 (n = 32) in sections I and II, respectively. The high nutritional condition of anchovy larvae indicates that the environmental characteristics observed in March in the study area would be appropriate for their growth and survival.

La población patagónica de Engraulis anchoita habita el sector costero comprendido entre los 42° y 46° S. Sus áreas de desove y cría se asocian al frente de marea de Península Valdés, que se forma a fines de la primavera y desaparece a principios de otoño. Las condiciones oceanográficas del frente generan una alta productividad primaria y elevada biomasa del zooplancton asociado, potencial alimento para larvas de peces. Se estimó la condición nutricional de larvas de anchoíta por medio de tres índices: el Factor de Condición de Fulton, la relación ARN/ADN y la performance de crecimiento. Se compararon dos secciones oceanográficas: una en la que se detectó la presencia del frente de marea y otra sin ese efecto. Los resultados de los índices evidenciaron una condición nutricional mejor en las larvas de anchoíta en la sección oceanográfica con persistencia del frente de marea. Para determinar las variables ambientales que influencian la condición larval de E. anchoita serealizó un estudio aplicando Modelos Lineales Generalizados, empleando el índice ARN/ADN como variable dependiente y la clorofila superficial, la abundancia de nauplii, el volumen de plancton gelatinoso y el largo estándar de las larvas como variables explicativas. Se observó una mejora de la condición nutricional con el incremento de la abundancia de nauplii de copépodos, alimento potencial de las larvas. En cambio, el índice ARN/ADN disminuyó con la abundancia de plancton gelatinoso, lo cual sugiere que en la zona estudiada, estos organismos competirían con las larvas de E. anchoita. The Patagonian population of Engraulis anchoita inhabits the coastal sector comprised between 42° and 46° S. Its spawning and rearing areas are associated with the tidal frontal system of Peninsula Valdés, which forms in late spring and breaks during early autumn. Oceanographic frontal conditions can enhance primary production and zooplankton biomass, representing an enriched food source for fish larvae. Larval nutritional condition was estimated using three indices: Fulton’s Condition Index, RNA/DNA ratio and growth performance. Two oceanographic sections were compared, one in which the presence of the frontal system was observed and another devoid of such effect. Condition indices reflected an enhanced nutritional condition of anchovy larvae in the section where the front persisted. Generalized linear models were applied to determine the effect of environmental variables on larval condition. RNA/DNA ratio was considered as the dependent variable, whereas surface chlorophyll concentration, copepod nauplii abundance, jellyfish volume and larval standard length were used as predictors. In general, the nutritional condition improved with the abundance of copepod nauplii, potential food source for the anchovy larvae. In contrast, the RNA/DNA ratio decreased with the increase of jellyfish abundance, suggesting that, in the study area, these organisms might act as competitors of anchovy larvae.

Diversos índices han sido empleados para caracterizar la condición nutricional en larvas de peces. Los criterios histológicos han demostrado ser confiables para diagnosticar la condición ya que involucran el estudio del aspecto de las células y la estructura e integridad de diferentes tejidos de las larvas. Sin embargo, debido a que el aspecto microscópico de los tejidos varía tanto como consecuencia de la condición nutricional como del estadio de desarrollo de las larvas, se hace necesario caracterizar las estructuras empleadas para diagnosticar su condición nutricional y tener en cuenta el estadio de desarrollo de los ejemplares. El objetivo principal de este trabajo fue una descripción micro-anatómica de los tejidos utilizados para determinar la condición nutricional de larvas de peces con larvas de Engraulis anchoita recolectadas en el mar Argentino. Se determinó un índice de condición histológica (ICH) para diferentes estadios de desarrollo de larvas de anchoíta, discriminándose entre los tejidos que muestran inanición sufrida a largo plazo y los que muestran inanición a corto plazo. Se observó una reducción en el ICH luego de la reabsorción del vitelo y hacia el final de la etapa larval. Los tejidos de corto plazo mostraron mayor sensibilidad a pequeños cambios en la condición nutricional. Diverse indices have been used to characterize the nutritional condition of fish larvae. Histological criteria were shown to be reliable in diagnosing nutritional condition, because they involve the study of cellular aspect, structure and tissular integrity. However, since the microscopical appearance of larval tissues varies both as a consequence of nutritional status and developmental stages, it becomes necessary to characterize the employed structures and to take into account the developmental stage of the studied specimen. The aim of this study was to develop a typical micro-anatomical description to assess the nutritional condition of Engraulis anchoita fish larvae collected in the Argentine Sea. Several tissues were diagnosed to calculate a histological condition index (ICH) in regards to anchovy larvae ontogeny. In addition, the tissues analysed were divided into short and long-term indices. A reduction of HCI was observed during yolk exhaustion and at the end of the larval stage. In order to detect slight changes in histological condition, short term tissues proved to be more sensitive to starvation than long term tissues.

El estudio de la condición nutricional de las larvas de peces permite evaluar individualmente el estado fisiológico de los ejemplares y detectar así áreas de cría favorables para la supervivencia y el crecimiento larval. En el presente trabajo se emplearon técnicas morfométricas, histológicas y bioquímicas para determinar la condición nutricional de larvas de anchoíta, Engraulis anchoita, recolectadas en el mar. Los resultados obtenidos fueron complementados con los datos oceanográficos y las abundancias de diferentes componentes del plancton, tanto predadores como presas de las larvas de anchoíta. Se ha observado que los factores que determinan la distribución de las larvas de esta especie serían principalmente de naturaleza físico-química. Si bien no se encontraron diferencias significativas entre áreas, la condición nutricional fue algo mejor en las zonas caracterizadas por aguas de mezcla dentro las estructuras frontales presentes en el área de estudio. Por otra parte, la condición nutricional se vería favorecida durante las estaciones del año en las que no se observan altas densidades larvales. Probablemente las condiciones sean propicias para el crecimiento larval durante todo el año y las densidades bajas o intermedias de larvas de peces permitan a las larvas de anchoíta evitar o reducir la competencia intra e interespecífica por el alimento. Por otra parte, muy pocas larvas presentaron valores bajos de condición nutricional, esto podría indicar que E. anchoita encuentra durante todo el año en la zona estudiada las condiciones ambientales adecuadas para su supervivencia y crecimiento larval. Nutritional condition studies allow the assessment of physiological state of each larva and thus, the establishment of favourable nursery areas which provide better survival and growth. In the present work, morphometrical, histological and biochemical techniques were employed to assess nutritional condition of anchovy, Engraulis anchoita, larvae captured in the sea. Its results were complemented with oceanographic data and information about zooplankton abundances, both prey and predators of anchovy larvae. Anchovy larvae abundance and distribution would be mainly determined by physico-chemical variables. Even though no significant differences were found in larval nutritional condition among the studied areas, larval condition was slightly better in frontal areas characterized by mixed water masses. On the other hand, anchovy larvae condition seems to be favoured during seasons when larval abundances remain low. Probably, ocean conditions are almost always favourable for larval growth and survival during the whole year, but low or intermediate larval densities allow avoiding both intra and inter-specific competition. As only a small number of anchovy larvae were described as in starving condition, it can be assumed that E. anchoita finds environmental conditions that favour its growth and survival. during all seasons in the studied area. Fil: Diaz, Marina Vera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.