Larval condition and growth of <i>Sardinella brasiliensis </i> (Steindachner, 1879): preliminary results from laboratory studies

Abstract

SUMMARY: Brazilian sardine, the most important resource along the southeastern Brazilian coast, presented great variations and declines in its stocks. The main factors contributing to this are: oceanographic structure changes; recruitment failures; excessive catches of juveniles and increase in fishery effort. In spite of this, no alterations in the density-dependent parameters were detected. Consequently, methods analysing the condition of the larvae coupled with methods determining growth using sagittae otolith increment width were applied to evaluate growth under experimental conditions. The results of the readings on the sagittae were compared with the age of the laboratory-reared sardine larvae and confirmed that increments are formed on a daily basis. Under poor feeding conditions, sardine larvae showed a low growth expressed by dry weight, RNA/DNA ratio and tryptic enzyme activity and by the narrow and low contrast increments in the otoliths. The results of the biochemical indices showed an unexpected decline in the feeding group coupled with a decrease in width of increment numbers 8 and 10. Other factors than food availability were affecting the condition of the larvae and might be indicative of physiological processes and ontogenetic changes occurring in sardine larvae.Key words: Brazilian sardine larvae, larval condition and growth, RNA/DNA ratio, tryptic enzyme activity, otolith microstructure.RESUMEN: CONDICIÓN LARVARIA Y CRECIMIENTO DE SARDINELLA BRASILIENSIS (STEINDACHNER, 1879): RESULTADOS PRELIMI-NARES A PARTIR DE ESTUDIOS DE LABORATORIO. -La sardinela brasileña, el recurso más importante en la costa sudeste del Brasil, presentó grandes variaciones y disminuciones en sus poblaciones. Los principales factores que contribuyeron a dicha situación fueron: los cambios en la estructura oceanográfica, los fallos en el reclutamiento, las capturas excesivas de juveniles y el aumento del esfuerzo pesquero. A pesar de ello, no se detectaron alteraciones en los parámetros denso-dependientes de la población. Consecuentemente, se aplicaron métodos de análisis de condición larvaria junto a métodos de determinación del crecimiento mediante la anchura de los incrementos de los otolitos sagitta para evaluar el crecimiento bajo condiciones experimentales. Los resultados de las lecturas de los sagitta se compararon con la edad de las larvas de sardinela cultivadas en el laboratorio y confirmaron que los incrementos se forman diariamente. Las larvas de sardinela sometidas a bajos niveles de alimentación mostraron un bajo crecimiento expresado en peso seco, relación RNA/DNA y actividad de la tripsina, y un bajo contraste de los incrementos en los otolitos. Los resultados de los índices bioquímicos mostraron un inesperado descenso en el grupo de larvas alimentadas, acompañado de una disminución en la anchura de los incrementos 8 y 10. Además de la disponibilidad de alimento, otros factores afectaron a la condición de las larvas y podrían indicar procesos fisiológicos o cambios ontogenéticos que tienen lugar en el desa...

Live diet for first feeding of Brazilian sardine, Sardinella brasiliensis (STEINDACHNER, 1879), larvae in captivity

“…In marine fish larvae, pancreatic and intestinal enzymes are generally low at first feeding and in some species are even not detected (Kolkovski, 2001). Previous studies of Brazilian sardine larvae also showed low levels of tryptic enzyme activity at a similar age and development stage (Bianco Rossi-Wongtschowski et al, 2003;Dias et al, 2004). Therefore, it is necessary to use more sensitive methods to clarify protease activity in Brazilian sardine larvae.…”

“…The use of microalgae in marine fish hatcheries is interesting from an economic, nutritional and environmental perspective (Benetti et al, 2008;Nielsen et al, 2017). One positive effect of the green water technique is the stability of the water (Conceição et al, 2010;Naas & Harboe, 1992), since microalgae release oxygen and consume nitrogen compounds (Muller-Feuga, 2000;Shan & Lin, 2014). To reduce costs, alternative products, such as preserved microalgae, have been proposed to replace live microalgae in marine aquaculture (Nielsen et al, 2017;Richmond & Hu, 2013).…”

“…Copepods, which are the main component in natural zooplankton, normally improve larvae growth, even if they are available in small amounts (Conceição et al, 2010).…”

“…Nevertheless, digestive enzymes from rotifer and copepods seem to have a low contribution to total digestive enzyme activity of clupeoid fish, such as Japanese sardine Sardinops melanoticus and herring Clupea harengus (Kolkovski, 2001). The distinct lipid profile commonly found in wild zooplankton or copepods (DHA 17-40% and EPA 4.4-17% of total lipids) compared with rotifer (DHA 11-12.4% and EPA 3.6-7% of total lipids) (Conceição et al, 2010;Kandathil Radhakrishnan et al, 2020;Van der Meeren et al, 2008) may have stimulated enzyme activity in Brazilian sardine larvae, rather than a direct contribution from lipase from live feed. Lipase activity in gilthead seabream larvae, for example, was clearly influenced by the fatty acid composition of dietary lipids (Izquierdo et al, 2000).…”

“…ones (incomplete digestive system and feed composition) (Cahu & Zambonino Infante, 2001;Conceição et al, 2010;Kolkovski, 2013).…”