Potential Interactions of Sediment Characteristics and Oxygen Availability: Effects on Embryonic Development of Rainbow Trout (Oncorhynchus mykiss)

Abstract

Increasing sediment influx from construction activities threatens salmonid spawning habitats, impacting the development and hatching success of embryos due to finer sediments. This study investigates the interplay between sediment coverage, grain size, and low dissolved oxygen levels on the mortality and hatching success of Rainbow trout (Oncorhynchus mykiss) embryos, from fertilization to hatching, using a dual-experiment approach in a laboratory setting. The first experiment evaluated fine sediment characteristics, while the second examined reduced oxygen levels, both focusing on egg mortality, development, growth, and hatching success.

Results indicated that finer sediments (<2 mm) influenced all biological endpoints to varying degrees. Thick layers caused early underdevelopment and death before hatching, while thin layers led to underdeveloped embryos and alevins with reduced growth. Mortality rates and hatching success were dependent on sediment fraction and layer thickness. Developmental delay and growth were primarily influenced by sediment fraction, with thick layers exaggerating these effects. Silt (0.063-0.002 mm) was the most harmful fraction, causing high mortality rates. Sand (0.63-0.2 mm) also significantly impacted parameters, with coarse sand (2.0-1.0 mm) causing high mortality post-hatching due to pre-hatching developmental issues, challenging previous studies. Mixed sediments (<2 mm), containing clay, resulted in the highest early mortality rates.

While a 70% oxygen level posed no significant effects, 40-50% oxygen levels led to high mortality rates, predominantly post-hatching. A notable correlation between finer sediments (<0.63 mm) and reduced dissolved oxygen (DO) levels was observed, suggesting oxygen availability may contribute to developmental delays and mortality in these sediments. However, even with sufficient oxygen, finer sediments still caused developmental delays and mortality, indicating that sediment characteristics and physical effects affect outcomes.

This study supports the theory that fine sediment characteristics and low dissolved oxygen levels detrimentally affect Rainbow trout embryo development. Nevertheless, further research is needed to explore embryo development and survival under sufficient oxygen levels beneath sediments. The findings highlight the need for effective mitigation strategies addressing both sediment size and quantity to reduce fine sediment runoff during construction activities.