Physiology and performance of wild and domestic strains of diploid and triploid rainbow trout (Oncorhynchus mykiss) in response to environmental challenges

Abstract

Physiology and performance of wild and domestic strains of diploid and triploid rainbow trout 1 (Oncorhynchus mykiss) in response to environmental challenges 2 3 by 4Abstract 11To determine the factors that may contribute to the poor survival of triploid (3n) rainbow trout 12 (Oncorhynchus mykiss) in lake stocking programs, we compared the physiology and responses to 13 environmental challenges of four wild strains and one domestic strain of diploid (2n) and 3n juvenile 14 rainbow trout. Over four successive years, wild trout were caught from nature, spawned and progeny 15 reared in a hatchery along with hatchery-bred domestic trout. Offspring of each strain were raised for 16 up to 12 months as both 2n and 3n and growth rate, critical swimming speed, routine oxygen 17 consumption rate, critical oxygen tensions, thermal tolerance, and hypoxia tolerance were assessed in a 18 laboratory setting. Cohorts of the 2008, 2009, and 2010 wild strains were also stocked into two 19 experimental lakes and recaptured as adults using traps and fyke nets in 2011 for laboratory analysis. In 20 the juvenile trout, the only measure of performance to show a consistent difference between 2n and 3n 21 individuals across all strains was hypoxia tolerance, where 3n trout had a shorter time to loss of 22 equilibrium (LOE) at 16torr than their 2n counterparts, but this effect was not seen in adult lake-reared 23 trout. Strain had a significant effect on specific growth rate, U crit and time to LOE in hypoxia, although 24 the effects of strain on these variables was not consistent from year-to-year. Overall, this study suggests 25 that poorer hypoxia tolerance in 3n trout compared with 2n trout may be a contributing factor to the 26 higher lake stocking mortalities in 3n trout. 27 28 the direction and magnitude of the difference. For example, even for growth rate, some studies show no 48 difference between 2n and 3n fish (O'Flynn et al. 1997) while other studies show that 3n fish grow faster 49 (Galbreath et al. 1994) or slower (McGeachy et al. 1995;McCarthy et al. 1996) than 2n fish. Many other 50 studies have shown minor or inconsistent differences in physiology and stress responses between 2n 51 and 3n fish, and there is little explanation for why 3n fish show higher mortality rates when stocked into 52 potentially stressful natural lake systems. To date, the best possible explanation for why 3n fish may 53show higher mortality rates in natural lakes is due to 3n fish being less tolerant of hypoxia exposure 54 compared with 2n fish (Yamamoto and Iida 1994;Lilyestrom et al. 1999), and hypoxia can be prevalent 55 in lakes due to turnover, eutrophication, and winter ice cover (Diaz and Breitburg 2009). However, 56comparing the effects of triploidy on fish across studies is difficult and confounded by differences in the 57 choice of species, strain, year, and rearing conditions, all of which can have their own effects on 58 physiology and performance (e.g. Guo et al. 1990). 59Numerous studies have shown that strain and population can affe...

A rainbow trout Oncorhynchus mykiss strain with higher aerobic scope in normoxia also has superior tolerance of hypoxia

“…The results of the present study clearly demonstrate intraspecific variation in O 2max , AAS, FAS, EPOC, O 2crit , ILOS and CT max among three strains of O. mykiss . In contrast, the majority of the previous studies that have independently examined variation in metabolic traits, hypoxia tolerance or upper thermal tolerance among strains of O. mykiss have found little evidence of intraspecific variation (Bidgood & Berst, ; Myrick & Cech, ; Rodnick et al., ; Scott et al., ). For instance, Scott et al .…”

“…Intraspecific differences in metabolic rate, aerobic scope, critical oxygen level, hypoxia tolerance and upper thermal tolerance are not novel observations in fish generally and several previous studies have assessed at least one of these traits in domestic or wild strains of O. mykiss from the U.S.A., Canada, Austria, Italy, Australia and Japan (Fry, ; Bidgood & Berst, ; Klar et al., ; Lee & Rinne, ; Wieser et al., ; Scarabello et al., ; Strange et al., ; Alsop & Wood, ; Currie et al., ; McGeer et al., ; Myrick & Cech, , ; Carline & Machung, ; Faust et al., ; Molony et al., ; Rodnick et al., ; Ineno et al., ; Galbreath et al., ; LeBlanc et al., ; Recsetar et al., ; Chen et al., ; Scott et al., ; Verhille et al., ). In particular, these studies have demonstrated substantial variation in upper thermal tolerance, hypoxia tolerance, routine O 2 and O 2max in O. mykiss , which could be indicative of a large amount of intraspecific variation in this species.…”

“…The main goals of the current study were to use individuals and strains of hatchery‐raised rainbow trout Oncorhynchus mykiss (Walbaum 1792) parr to assess: the relationships between critical oxygen level (O 2crit ) and standard metabolic rate (SMR), maximum oxygen uptake rate (O 2max ) or absolute aerobic scope (AAS); the incipient lethal oxygen saturation (ILOS; a measure of hypoxia tolerance) and critical oxygen level (O 2crit ) or accumulated oxygen deficit (AOD). Oncorhynchus mykiss is a good candidate species in which to study these relationships, because several of these traits have been independently demonstrated to differ among stains of this species (Carline & Machung, ; Chen et al., ; Scott et al., ). In the current study, these traits were measured as components of the integrated respiratory assessment paradigm (IRAP) (Zhang et al., , ), which also includes calculations of factorial aerobic scope (FAS), excess post‐exercise oxygen consumption (EPOC), scope for oxygen deficit (SOD) and factorial scope for oxygen deficit (FSOD), allowing strain‐level differences in these traits to be assessed as well.…”

Selection for upper thermal tolerance in rainbow trout (Oncorhynchus mykissWalbaum)

“…5). CT max has a smaller range between 27.5 and 30°C for indigenous strains in British Columbia, Canada, when acclimated at 10°C (Scott et al, 2014) and in California, USA Cech, 2000, 2005), and in recently established strains in Pennsylvania, USA (Carline and Machung, 2001). For related redband trout that have adapted to a desert environment (Rodnick et al, 2004), where summer water temperature can oscillate from 18 to 30°C daily, CT max (29.7±0.3°C) was close to the upper daily water temperature recorded for those streams.…”

The effects of strain and ploidy on the physiological responses of rainbow trout (Oncorhynchus mykiss) to pH9.5 exposure

“…This lake-stocking program uses trout from at least 6 different strains of which roughly half are stocked as triploids. Triploidy is a condition that is produced by hatcheries in an attempt to induce sterility and promote growth, but triploid fish tend to be more sensitive to environmental challenge (Ojolick et al, 1995;Cotter et al, 2002;Scott et al, 2014). The increasing pH in many of BC lakes, particularly popular fishing lakes such as Green Lake, which has already reached a pH of~9.3, is of great concern for fisheries biologists and puts continued stocking efforts in jeopardy.…”