• Source: Owens sucker

The Owens sucker (Catostomus fumeiventris) is a fish in the family Catostomidae that is endemic to California. The name fumeiventris has a Latin origin, with fumeus meaning "smoky" and ventris meaning "belly". Originally described as a population of sandbar suckers, it became recognized as its own species in 1938. Owens suckers are closely related to the Tahoe suckers and possess the ability to hybridize with Santa Ana suckers.




Description



The Owens sucker has an inferior mouth facing the bottom of water sources, and it has pectoral fins flattening out, suggesting it prefers staying near the bottom of the river or lake bed. Tending to feed at night, this fish often feeds on algae and other organic matter that sinks to the bottom of these waterways. It has 10 dorsal fin rays with a dusky abdomen more pronounced in nuptial males and lacks the red lateral stripe of a similar species, the Tahoe Sucker. The Owens sucker is similar to the Tahoe sucker (Catostomus tahoensis), but it has coarser scales and is duller in colour. The Owens Sucker larva has a more complete line of melanophores around its gut when compared to the Tahoe sucker. Owens suckers also have differently shaped mouths when compared. The Owens sucker has fewer than 80 lateral line scales as opposed to the Tahoe suckers possessing more than 80 lateral line scales, making for easier distinctions. The adults are slaty coloured, although some individuals can be very dark, with dusky bellies, which are especially noticeable in spawning males. It grows to a maximum size of 50 cm but is usually found around 30 cm in total length.




Environment


Owens suckers prefer to live in water with temperatures between 7 and 13 degrees Celsius and pH values ranging from 7.9 to 8.0. Despite their "least concern" conservation status, rising temperatures from climate change could potentially push water temperatures beyond the preferred range for Owens suckers, making continuous monitoring of this species important for its survival. Owens suckers favour waterways with finer substrates as opposed to areas with gravel or rocks. Although they have been introduced to other waterways, they are only native to one watershed, and the territories they occupy are very scarce due to human interaction. These fish, however, are very adaptable and succeed in their ability to repopulate habitats and compete with non-native species.




Distribution



It is endemic to the Owens River in the Owens Valley of eastern California and has been introduced into June Lake in the Mono Lake basin and to the Santa Clara River system as a result of a release of water from the Owens River through the Los Angeles Aqueduct. It is abundant in the Crowley Lake with populations in Convict Lake and Lake Sabrina and populations have been established in the Owens River sanctuary. This species is also present in Sespe Creek near the outlet of the Fillmore Hatchery and Piru Creek above Piru Lake California. The endemic location of the Owens sucker, Owens Valley, originally lacked aquatic diversity with only 2 minnow species, the Owens Sucker, and a killifish notably missing any species of trout which were common in areas North and West of the Owens Valley. The exact population in the Santa Clara system is uncertain but introduced Owens Suckers often end up hybridizing with the native Santa Ana suckers in this region.




Conservation status


During the 1870s, irrigation projects diverted water away from Owens Valley drastically altering the aquatic systems. Around 1890, catfish, carp, and salmon were introduced into this basin leading to a serious decline in native fish populations for the past 75 years. While several native fish such as the Owens Pupfish and Owens Tui Chub are endangered and Owens speckled dance are a "species of concern" , the Owens Sucker is seen as least concerned. Approximately 83% of California's inland fish species are either extinct or experiencing population declines. Despite this, when evaluated on a 1–5 scale taking into account factors such as area occupied, climate change resistance, and overall tolerance, the Owens Sucker received a value of 3.9 inferring its population is relatively stable but should still be monitored. Threats that pose the largest threat to the Owens Sucker include the construction of dams regulating the Owens river, urbanization of areas near the Owens river, and predation of alien species. Factors such as grazing,wildfires, and harvesting are seen as negligible when considering the conservation of this species. Formerly large numbers of adults would gather below the outlet of the Fillmore Hatchery for weeks in March but have had decreasing numbers losing roughly half of their numbers within the past 4 years.
California has looked into an umbrella species program, where the conservation and monitoring of select species enhances overall aquatic community protection and ensures the maintenance of streamflow conditions. The selection of which Freshwater California species that would become the umbrella species remains controversial but upon the list of potential candidates the Owens Sucker is present alongside other California freshwater fish including the White Sturgeon, Santa Ana Sucker, and Sacramento Pikeminnow.




Biology


Owens suckers are nocturnal, their diet consists of aquatic insects, algae, detritus, and organic matter. They spawn from May through to early July over gravel substrates, in tributaries, although lake living populations will also spawn over gravelly areas of the lake beds and springs. The lifecycle of the Owens Suckers can be split into 3 phases of prolarvae, postlarvae, and juveniles. Prolarvae measure at around 11–12 mm in length and have yolk the full length of their gut. At around 12mm most prolarvae have successfully transitioned into postlarvae. The pelvic fin for the Owens Sucker does not appear until the fish reaches lengths of around 18–22mm in which they are small buds. The larvae become juveniles once the attain a total length of 19–22mm.At this stage the fin rays become fully developed and the anterior gut begins having a darker pigment.The juveniles hide along stream margins and in backwaters among weeds.
When reproducing, the genes undergo "gene silencing" where one pair of genes becomes inactive, often allowing for evolutionary advancements in their morphology. While being tetraploid, the Owens Sucker may behave as if it were a diploid due to many of their genes being silenced. On average, the Owens Sucker only expresses 42% of their duplicated genes. It grows to a maximum size of 50 cm but is usually found around 30 cm in total length. Closely related species such as the Tahoe sucker have diploidization events occurring in their genome inferring that with more research the Owens sucker may also be capable of returning its genomes back to its diploid state.
Comparisons between the Owens Sucker and the Owens Tui Chub supports the hypothesis that the Lahontan basin and the Owens River Basin were once connected and split apart due to geological changes such as the formations of the Owens River gorge. Additionally the genetic values or FST values when compared to the Speckled Dace furthermore prove this theory that these species may have separated due to a volcanic event around 760,000 years ago.




References

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