Forster, I. | bioRxiv Science

bioRxiv2022

Food quantity does not compensate for poor food quality in fitness of juvenile Chinook salmon (Oncorhynchus tshawytscha)

The global temperature increase due to global change is predicted to be between 3.3 - 5.7{degrees}C by 2100 leading to changes at the base of the marine food web in species composition, abundance, and quality at the base of the marine food web leading to flow-on effects of higher trophic levels such as fish and humans. Changes in marine prey availability and nutritional quality can affect juvenile salmon conditions (i.e., growth, condition, and mortality) during the early marine phase. There is limited knowledge of the interplay between prey availability and prey quality and the importance of food quality under food-satiated conditions. Here, a three-phase feeding experiment measured the effects of nutritional quality (fatty acid composition and ratios) on juvenile Chinook salmon (Oncorhynchus tshawytscha) condition. Experimental diets represented the present three different climate scenarios with a present-day diet (Euphausia pacifica), a control diet (commercial aquaculture diet), and a predicted IPCC worst-case scenario diet with low essential fatty acid concentrations (IPCC SSP5-8.5). We tested how potential future low quality food affects growth rates, body condition, fatty acid composition and mortality rates in juvenile Chinook salmon compared to present-quality prey. Fatty acids were incorporated into the salmon muscle at varying rates but, on average, reflected dietary concentrations. High dietary concentrations of DHA, EPA and high DHA:EPA ratios resulted in increased fish growth and condition. In contrast, low concentrations of DHA and EPA and low DHA:EPA ratios in the diets were not compensated for by increased food quantity. This result highlights the importance of considering food quality when assessing fish response to changing ocean conditions. HighlightsO_LIClimate change may decrease the quality of salmon prey through changes in the fatty acid composition. C_LIO_LILow dietary essential fatty acid levels reduce growth and condition and increase mortality rates in juvenile Chinook salmon. C_LIO_LIFood quality changes within zooplankton species but also by changes between species. C_LIO_LIResults suggest potential cascading effects on higher trophic levels when zooplankton species composition shifts to lower quality species. C_LIO_LIHigher food intake cannot compensate for low food quality. C_LI

ecology↗

bioRxiv2022

Dynamic coastal pelagic habitat drives rapid changes in growth and condition of juvenile sockeye salmon (Oncorhynchus nerka) during early marine migration

Migrating marine taxa encounter diverse habitats that differ environmentally and in foraging conditions over a range of spatial scales. We examined body (RNA/DNA, length-weight residuals) and nutritional (fatty acid composition) condition of juvenile sockeye salmon (Oncorhynchus nerka) in British Columbia, while migrating through varied oceanographically waters. Fish were sampled in the stratified northern Strait of Georgia (NSoG); the highly mixed Johnstone Strait (JS); and the transitional zone of Queen Charlotte Strait (QCS). In 2015, body and nutritional condition were high in the NSoG and responded rapidly to reach lowest levels in JS with its low prey availability, and showing signs of compensatory growth in QCS. In 2016, juvenile salmon had significantly lower condition in the NSoG than in 2015, although zooplankton biomass was similar, condition remained low in JS, and no compensatory growth was observed in QCS. We provide evidence that differences in juvenile salmon condition between the two years being due to changes in the food quality available to juvenile fish. Further, we propose that the TGH needs to be extended to incorporate food quality as a parameter to understand changes in fish condition and survival between years.

ecology↗