Nutritional condition of fish larvae in South African estuaries: an appraisal of three biochemical methods

Abstract

Estuaries are exposed to a number of threats and many South African estuarine systems are functionally and structurally altered. The extent to which fish are affected by these alterations is not fully understood. The estuarine round herring Gilchristella aestuaria is an appropriate species to use when examining such effects. The most widely used approaches to evaluating the nutritional condition of fish larvae are based on biochemical methods. In order to identify the most suitable technique for assessing body condition of fish larvae in estuaries, the nutritional condition of post-flexion larvae of G. aestuaria from the Sundays and Kariega estuaries on the south-east coast of South Africa was evaluated using three different biochemical techniques: (i) total lipid content analysis and the triacylglycerol/cholesterol (TAG/CHOL) ratio; (ii) protein content analysis; and (iii) the RNA/DNA ratio. Results from techniques (ii) and (iii) revealed that G. aestuaria larvae from the Kariega Estuary were in better condition than larvae from the Sundays Estuary, probably due to a recent plankton bloom. It is concluded that the individual RNA/ DNA ratio can provide a reliable, sensitive and cost-effective method to assess the immediate effects of environmental changes on the nutritional condition of estuarine fish larvae.

Lipids as biomarkers to assess the nutritional and physiological status of two diadromous fish (Anguilla anguilla and Chelon auratus) at early life stages in a temperate macrotidal estuary

“…TAGs are catabolized early during a period of starvation while PLs remain constant for a given organism size. Following this assumption, Fraser (1989) developed the TAG:PL indice to assess the level of available reserves and the nutritional status of early life stages of fish (Costalago et al, 2014; Di Pane, 2019; Giraldo et al, 2011; Peters et al, 2015; Rainuzzo et al, 1997). Additionally, the nutritional status of larvae directly influences their survival probability.…”

eDNA metabarcoding vs metagenomics: an assessment of dietary competition in two estuarine pipefishes

“…Estuaries are semi-closed bodies of water with simultaneous connections to both rivers and the ocean (Costalago et al, 2014). The resulting fluctuations in salinity and temperature (James & Harrison, 2010) make estuaries unique and challenging habitats, inhabited only by species that can tolerate such conditions (Harrison & Whitfield, 2012).…”