Oxygen concentration in the water boundary layer next to rainbow trout (Oncorhynchus mykiss) embryos is influenced by hypoxia exposure time, metabolic rate, and water flow

Abstract

The objective of this study was to examine the influence of hypoxia exposure time, metabolic rate, and water flow rate on the O2 concentration in the boundary layer outside and inside the chorion of rainbow trout ( Oncorhynchus mykiss ) embryos. Oxygen consumption, growth, and dissolved O2 in the boundary layer were measured at 15, 22, and 29 days post fertilization (dpf) from embryos reared in normoxia (O2 concentration at 100% saturation) and chronic hypoxia (>24 h, 50% saturation) and exposed to acute hypoxia (30 min, 50% saturation). Chronic and acute hypoxia exposure decreased the dissolved O2 in the boundary layer to the same extent at 15 and 22 dpf; however, at 29 dpf, O2 levels were significantly lower in acute relative to chronic hypoxia. At 29 dpf, O2 uptake per individual was significantly lower in embryos exposed to chronic relative to acute hypoxia. In addition, mass-specific O2 uptake in chronic hypoxia-exposed embryos was ~40% less than that of controls but the same as that of acutely exposed embryos. This correlates with reduced growth in embryos exposed to chronic hypoxia. We conclude that boundary layer O2 is lower after 30 min of hypoxia compared with 2 weeks of hypoxia simply because embryos exposed to chronic hypoxia grow slower and consume less O2.

Fish embryos on land: terrestrial embryo deposition lowers oxygen uptake without altering growth or survival in the amphibious fishKryptolebias marmoratus

“…We propose that the lower metabolic rate in the terrestrial environment is related in part to fewer opercular movements. In encapsulated fish embryos, relatively thick boundary layers develop in low flow environments that may impair oxygen transport in aquatic environments (Ciuhanda et al, 2007;Miller et al, 2008;Dhiyebi et al, 2013). We found evidence to support the hypothesis that embryos manipulate their micro-environment to maintain oxygen delivery.…”

“…Matschak et al, 1997;Barrionuevo and Burggren, 1999;Miller et al, 2008). Hypoxia delays development in fishes (e.g.…”

Hypoxia delays hematopoiesis: retention of embryonic hemoglobin and erythrocytes in larval rainbow trout,Oncorhynchus mykiss, during chronic hypoxia exposure

“…This level of O 2 saturation has been observed previously in salmonid redds (Coble, 1961;Peterson and Quinn, 1996;Youngson et al, 2004) and was shown to significantly affect metabolic rate and cardiac development in embryonic rainbow trout (Miller et al, 2008;Miller et al, 2011). Hypoxia was generated by introducing N 2 gas into a header tank (~16 l).…”

“…Dissolved O 2 was monitored daily in the normoxic (98.7±0.4%) and hypoxic (29.7±0.5%) treatment tanks throughout the experiment (Hach LDO101 electrode connected to Hach HQ30d meter, Hach Company, Mississauga, ON, Canada). Because hypoxia exposure delays salmonid development (Shumway et al, 1964;Hamor and Garside, 1976;Ciuhandu et al, 2005;Miller et al, 2008), embryo sampling was stage-matched for the two treatment groups. Embryos were sampled at Vernier Stages 27 (prehatch; circulatory system is formed and functioning), 30 (hatch), 32 and 33 (in preliminary experiments a large increase in P 50 was observed between these stages), and 35 (near-complete yolk absorption; Fig.…”

“…1) (Garside, 1966;Miller et al, 2008), as well as distinct alterations of the blood-O 2 transport system. The first possibility is that the decrease in overall Hb concentration and retention of embryonic erythrocytes in stage-matched hypoxia-reared larvae may be associated with a general metabolic depression.…”