Male age at maturity in Chinook salmon Oncorhynchus tshawytscha is a heritable trait in which the physiological “decision” to mature depends on an individual's exceeding a body size or condition threshold at critical developmental periods. In Chinook salmon, high juvenile growth rates promote the so called “jack” male life history. Jack males mature 1 year earlier than the youngest females in a population and are substantially smaller than older (hereafter, “adult”) males from the same population. We tested the hypothesis that the offspring of jack Chinook salmon males grow faster than the offspring of adult males, consistent with the heritability for age at maturity already demonstrated for this species. We controlled for maternal effects by artificially spawning individual jack and adult males with the same female, incubating the eggs, and testing offspring growth and survival in a common, quasinatural stream environment. Paternal life history had a significant effect on final length and weight over all stream channel sections combined. The mean difference in body size between the offspring of jack and adult males ranged from essentially none to 31% among the eight stream channel sections. The size differences we detected could significantly affect which fish mature and thereby suggest that paternal effects on juvenile growth rate constitute a plausible proximate mechanism in maintaining life history diversity in Chinook salmon. Maternal body size was positively correlated with offspring growth rate and egg size was negatively correlated with growth rate, suggesting that fairly complex mechanisms regulate the growth rate through early ontogeny. The effect of sire life history on offspring growth is consistent with estimates of high heritability for age at maturity in Chinook salmon and a genetic effect of alternative mating tactics on offspring performance.
Female steelhead trout (Oncorhynchus mykiss) reared for 1 year (traditional, “S1”) and 2 years (experimental, “S2”) in captivity in the Methow River Basin, Washington, produced very similar numbers of offspring in replicate spawning channels over 3 consecutive years. In contrast, S1 anadromous males outcompeted S2 males for access to nesting females and, as a result, produced significantly more offspring. Male dominance was positively associated with body mass, but body mass did not account for differences between S1 and S2 males. Much smaller precocious S2 males that matured during rearing in hatchery raceways sired offspring in all six breeding groups. Contributions from precocious males were nearly always the result of sneak spawning events, although on rare occasions, precocious males were able to stimulate females to spawn in the absence of an anadromous male. Similarities in female breeding success suggest that S1 and S2 hatchery steelhead should exhibit similar productivity under natural conditions, but S1 male steelhead may result in greater rates of gene flow from hatchery to natural populations.
The effects of domestication selection on fitness are of serious concern in hatchery‐reared anadromous salmonids, which often experience selection for rapid growth and associated deviations from natural agonistic and feeding behaviors. The high rations that are used to raise age‐1 smolts and the reduced rations that are used to produce age‐2 smolts potentially result in very different behavioral tactics and social dynamics of competition in hatchery tanks. Consequently, steelhead Oncorhynchus mykiss hatchery programs with recovery or conservation goals may need to change their aquaculture practices to minimize domestication selection. This study investigated how the feeding rate (proportion of presented food items that were successfully captured) and relative competitive ability (ability to monopolize food items in small groups) of age‐1 and age‐2 steelhead corresponded to feeding location (surface or bottom) and growth rate in hatchery rearing tanks. We raised steelhead from a common broodstock to smolt at age 1 or age 2 by manipulating their rations (age‐1 fish received the high ration, age‐2 the low ration). The fish in the age‐1 treatment had a lower feeding rate than did those in the age‐2 treatment. Feeding rate was positively correlated with both body size and with growth rate in the rearing tanks at both rations. The age‐2 steelhead were more likely to be detected at a single feeding location than were the age‐1 fish, which were more frequently detected at both locations. The more competitive age‐1 fish were more frequently detected at both feeding locations, and the less competitive fish were detected at only one location. Relative competitive ability was not associated with feeding location in the age‐2 treatment, nor was it associated with growth rate in either treatment. Age‐2 steelhead that were detected only at the bottom or at both feeding locations had higher growth rates than those that were detected only at the surface, suggesting greater scramble competition near the point of food delivery under the restricted ration. Feeding location was not associated with growth rate in the age‐1 treatment. The results indicate that ration directly affects feeding rate and that ration and relative competitive ability interact to influence feeding rate. Because feeding rate was positively associated with growth rate at both ration levels in the hatchery tanks, behaviors that are associated with feeding motivation may be an important trait under selection in salmonid hatcheries.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.