Resumen del producto

We evaluated the relative size of the hepatopancreas (HP) in relation to the cephalothorax length (as a hepato-somatic index, HSI) and its association with instantaneous growth rate (IGR) from five euphausiids species: Euphausia pacifica and Thysanoessa spinifera collected off Oregon, USA in August-September 2010, Nyctiphanes simplex and Nematoscelis difficilis collected in the Gulf of California, Mexico in March and October 2010, and Euphausia mucronata collected off Antofagasta and Concepcion, Chile in Autumn/Spring/Summer 2010. Previous studies using this method have focused on Antarctic krill species. Euphausiids had significantly higher HSI in spring-summer when coastal upwelling promotes more favorable conditions for feeding. HPs with opaque and bright coloration were associated with poor/famine and healthy/well-fed conditions, respectively. Krill incubations showed that changes in the HSI are strongly associated with the food concentration and that they responded relatively fast (days) to changes in trophic conditions. Total length-HP regressions allowed us to identify a similar pattern for all krill species studied even though they inhabit different latitudes and ecosystems. Due to variability in HP shape, we propose to estimate the area of the HP and cephalothorax rather than measure only the longest axis of the HP, as in previous studies. We suggest that the study of the change of the HSI is a useful indicator of physiological condition at both the individual and population levels and can be utilized in regions with high environmental variability (temperate and subtropical regions) in addition to polar ecosystems.

Palabras clave: Nyctiphanes simplex; Growth; hepatopancreas

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