Size, fecundity and condition factor changes in endangered delta smelt <i>Hypomesus transpacificus</i> over 10 generations in captivity

Ellison, Lars M.; Rahman, Md. Moshiur; Finger, Amanda J.; Sandford, Marade; Hsueh, Chih-Hsin; Schultz, Andrew A.; Hung, Tien‐Chieh

doi:10.1002/aff2.116

Cited by 5 publications

(7 citation statements)

References 68 publications

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“…Therefore, we hypothesize that the loss of plasticity in high DI fish may be adaptive in that they can direct energy toward other processes (such as growth and reproduction) rather than energy required for plasticity maintenance. Indeed, higher DI fish are larger and have a higher body conditioning (Ellison et al., 2023). While there are likely many selective pressures in the hatchery that have contributed to the observed higher fitness of high DI genotypes, one possible contribution could come from the lower fitness costs related to plasticity maintenance.…”

Section: Discussionmentioning

confidence: 99%

“…The FCCL sorted through tagged fish twice per week to identify ripe females (i.e., ready to spawn). Once a suitable genetic match was identified for the selected ripe females (see Genetic management of spawning ), the FCCL conducted strip spawning by combining manually expressed eggs from a ripe female with manually expressed milt from a mature male (Ellison et al., 2023). Approximately equal numbers of fertilized eggs from eight single‐pair crosses were then combined into one incubator for hatching, creating a multi‐family group.…”

Section: Methodsmentioning

confidence: 99%

“…Measuring growth and the size of delta smelt at age at maturity may also elucidate possible mechanisms of plasticity (Mobley et al, 2020(Mobley et al, , 2021. Captured delta smelt individuals have been shown to have longer fork lengths and higher body conditions than wild-caught individuals at the time they are spawned (Ellison et al, 2023), but growth indices were not collected when fish were tagged as mature (fish are not usually spawned as soon as they are mature, thus allowing more time for growth before they are spawned). Further research could investigate whether age at maturity is correlated with growth indices among different DI groups.…”

Section: Age At Maturity Is a Plastic Trait Relative To When Fish Are...mentioning

confidence: 99%

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Loss of plasticity in maturation timing after ten years of captive spawning in a delta smelt conservation hatchery

LaCava,

Griffiths,

Ellison

et al. 2023

Evolutionary Applications

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Adaptation to captivity in spawning programs can lead to unintentional consequences, such as domestication that results in reduced fitness in the wild. The timing of sexual maturation has been shown to be a trait under domestication selection in fish hatcheries, which affects a fish's access to mating opportunities and aligning their offspring's development with favorable environmental conditions. Earlier maturing fish may be favored in hatchery settings where managers provide artificially optimal growing conditions, but early maturation may reduce fitness in the wild if, for example, there is a mismatch between timing of reproduction and availability of resources that support recruitment. We investigated patterns of maturation timing in a delta smelt (Hypomesus transpacificus) conservation hatchery by quantifying changes to the median age at maturity since the captive spawning program was initiated in 2008. Over the span of a decade, we observed a small, but significant increase in age at maturity among broodstock by 2.2 weeks. This trait had low heritability and was largely controlled by phenotypic plasticity that was dependent on the time of year fish were born. Fish that were born later in the year matured faster, potentially a carryover from selection favoring synchronous spawning in the wild. However, higher DI (domestication index) fish showed a loss of plasticity, we argue, as a result of hatchery practices that breed individuals past peak periods of female ripeness. Our findings suggest that the hatchery setting has relaxed selection pressures for fish to mature quickly at the end of the year and, consequently, has led to a loss of plasticity in age at maturity. Hatchery fish that are re‐introduced in the wild may not be able to align maturation with population peaks if their maturation rates are too slow with reduced plasticity, potentially resulting in lower fitness.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Age At Maturity Is a Plastic Trait Relative To When Fish Are...mentioning

confidence: 99%

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Loss of plasticity in maturation timing after ten years of captive spawning in a delta smelt conservation hatchery

LaCava,

Griffiths,

Ellison

et al. 2023

Evolutionary Applications

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“…However, one female (ID: YT04) was used in a partial-factorial cross and a pooled cross due to the limited availability of ripe females (Table S2). The experimental crosses were made by manually expressing and combining gametes from the fish that were selected for each cross (Ellison et al 2023). For the pooled crosses, milt from three males was admixed in an extender vial (Rahman et al 2023) and then added into a container with premixed eggs from three females (Figure 1A).…”

Section: Experimental Crossesmentioning

confidence: 99%

Assessing captive spawning strategies for supplementation production of Delta Smelt

LaCava,

Donohue,

Badger

et al. 2023

Trans Am Fish Soc

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To support the declining wild population of Delta Smelt, a conservation hatchery has expanded its mission from maintaining a backup population as insurance against extinction to also producing fish for release into the wild. The substantially higher production demands require a balance between producing large numbers of fish while adhering to conservation genetic principles that maximize retention of effective population size (Ne) and thus overall diversity. We performed spawning experiments at the hatchery to evaluate the genetic consequences of two spawning strategies: 1) a pooled strategy where we fertilized premixed eggs from three dams with premixed milt from three sires and 2) a partial‐factorial strategy where eggs from three dams were mixed and then apportioned among three containers; each container then received milt from one sire. We used genetic parentage analysis of larval offspring to determine the reproductive success of spawners in ten replicate crosses of each strategy. Contributions of parents to offspring were more even in partial‐factorial crosses and consequently resulted in higher Ne (average Ne = 5.50 ± 0.38; expected Ne = 6.0), suggesting its potential for maintaining genetic diversity over time. In contrast, our pooled spawning experiment produced lower and more variable Ne values (average Ne = 3.86 ± 1.30), demonstrating that this more efficient method of production entails high costs in terms of long‐term genetic management. Treating our experiments as hypothetical pools of fish for release, we combined Ne values for pooled or partial‐factorial crosses to calculate the effective size of a release population (NeR). Unequal family sizes reduced the NeR for our pooled experiment to half of the expected value, whereas the partial‐factorial experiment NeR was 88% of the expected value. We discuss the benefits and risks of each method and how these can be considered when designing a spawning strategy for Delta Smelt supplementation.

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“…Cultured Delta Smelt also differ from wild conspecifics in several ways. For example, cultured females are longer, heavier, and more fecund than wild ones (Ellison et al 2023). However, the complete extent and nature of these differences has not been fully explored.…”

Section: Researchmentioning

confidence: 99%

A Qualitative Comparison of Spawning Behavior Between Cultured and Wild Delta Smelt (Hypomesus transpacificus)

Tsai,

Chase,

Carson

et al. 2023

SFEWS

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For many imperiled species, comparisons between wild and cultured populations are invaluable for informing conservation measures, though opportunities to do so may be rare. In this study, we asked whether spawning between and among wild and cultured Delta Smelt varies in terms of behavior or resulting egg fertilization success. We conducted two laboratory experiments in which we allowed wild females to spawn with wild males (wild × wild) and cultured females to spawn with wild males (cultured × wild). Due to small sample sizes, we qualitatively compared our results to published studies of all cultured Delta Smelt (cultured × cultured). Across all three groups, Delta Smelt exhibited spawns that were similar in sequence and manner, varied widely in diel timing, and occurred predominantly between a single female and one or two males. Egg fertilization success was higher in wild × wild trials than in cultured × wild ones, but both fell within the wide range observed among cultured × cultured fish. Thus, spawning was generally similar between cultured and wild Delta Smelt, whether they were in same- or mixed-origin groups. These findings provide rare insight into the spawning behavior of wild Delta Smelt and inform ongoing conservation efforts.

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Size, fecundity and condition factor changes in endangered delta smelt Hypomesus transpacificus over 10 generations in captivity

Cited by 5 publications

References 68 publications

Loss of plasticity in maturation timing after ten years of captive spawning in a delta smelt conservation hatchery

Loss of plasticity in maturation timing after ten years of captive spawning in a delta smelt conservation hatchery

Assessing captive spawning strategies for supplementation production of Delta Smelt

A Qualitative Comparison of Spawning Behavior Between Cultured and Wild Delta Smelt (Hypomesus transpacificus)

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