Bubyr caucasicus (Iljin 1930), Bubyr caucasicus kosswigii (Sözer 1941), Gobius caucasicus (Kavraiskii 1899), Gobius lencoranicus (Kessler 1877), Pomatoschistus caucasicus (Berg 1916)

Nonindigenous Occurrences: Knipowitschia caucasica has been introduced to the Aral Sea (Baimov 1963), to reservoirs in the Metsamor River, and Ararat Valley reservoirs of Armenia (Gabrielyan 2001). It has been recorded in the Morinj Bay, Kaštela Bay, Prokljan Lake, Karišnica River, the mouth of the Pantan River, and Cetina River in Croatia (Kovacic and Pallaoro 2003). It has been accidentally introduced to Lake Trichonis, and has been recorded in the Aliakmon and Itamos Rivers in Greece (Economidis et al. 1981; Economidis and Miller 1990; Daoulas et al. 1993). A Knipowitschia caucasica female was collected in a freshwater Szamos River in the Carpathian basin, Hungary, and it is thought to have been accidentally introduced (Halasi-Kovács et al. 2011). It has been reported to occur in Lake Manyas, Lake Sapanca, Sea of Marmora, Lake Eber, Lake Egirdir , and Demirköprü Barrier Lake in Turkey (Gheorghiev 1964; Economidis and Miller 1990; Van Neer et al. 1999).

Knipowitschia caucasica exhibits short generation time and early maturation (Kevrekidis et al. 1990). Eggs are found attached to gravel, dead bivalve shells, and dead roots of reeds (Baimov 1963). After hatching, the fish grows rapidly in its first summer and continues through the fall, reaching maturity after its first winter. In the northern hemisphere, this species reproduces from the end of April to the end of July in water temperatures of 15–27°C. Fecundity in the North Aegean Sea was 60–217 eggs per female, with an average of 109.8 eggs, while it was 97–343 per female in the Aral Sea. The highest reported fecundity was 1389 eggs in the Black Sea (Gheorghiev 1964). The fish usually lives for 1 to 2 years.

Potential pathway(s) of introduction: Transoceanic shipping (ballast water)

Knipowitschia caucasica does not occur near waters connected to the Great Lakes basin. This species is not known to hitchhike or foul. Knipowitschia caucasica is not stocked, commercially cultured, or sold in the Great Lakes region. It occurs in the Mediterranean Sea, which has shipping traffic that goes directly to the Great Lakes, however, there is insufficient information to determine if this species occurs in the Mediterranean ports that are in direct trade with the Great Lakes. Knipowitschia caucasica may be introduced to the Great Lakes via ships declaring “No Ballast on Board” (NOBOB), which are exempt from ballast water exchange. Holeck et al. (2004) specifically states this introduction will be through BOB (ballast on board) water or NOBOB residual water. The majority of ships entering the Great Lakes are NOBOB vessels and 43% of these ships contain residual water with less than 10‰ salinity (NOAA Final Report 2005). In the study, the temperature of the residual water from the vessels sampled ranged from -0.7 to 23.9°C; thus Knipowitschia caucasica is likely to survive the salinity and temperature of the NOBOB ballast water.

Knipowitschia caucasica has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: Moderate).

The native and introduced ranges of Knipowitschia caucasica have similar climatic and abiotic conditions as the Great Lakes (Reid and Orlova 2002; Grigorovich et al. 2003; U.S. EPA 2008). This species inhabits shallow waters that have varied bottom structures (Kovacic and Pallaoro 2003), which are available in the Great Lakes region. Knipowitschia caucasica can tolerate a wide range of abiotic conditions. It resides in hypersaline and fresh waters (Kevrekidis et al. 1990), so it may survive the transition in salinity between ballast water and Great Lakes fresh water. Further, increased salinization due to climate change would make the Great Lakes a better environment for the establishment of this species.  It occurs in the eutrophic Lake Egirdir (Gülle et al. 2008) as well as Lake Trichonis, a mesotrophic lake (Daoulas et al. 1993). It tolerates water temperatures of 1.6–26.9°C and oxygen levels of 5.3–8.96 ppm (Kevrekidis et al. 1990; Gülle et al. 2008); thus it is somewhat likely that this species can overwinter in the Great Lakes but its capacity to do so is limited by the amount of dissolved oxygen in the water. In its current range, Knipowitschia caucasica migrates into deeper waters over the winter (Baimov 1963) where temperatures may be slightly higher, but dissolved oxygen is lower.

Knipowitschia caucasica has a broad and flexible diet, and feeds primarily on benthic amphipods, polychaetes, chironomid larvae, copepods, and cladocerans (Kevrekidis et al. 1990). These fish are also known to feed on Dreissenid polymorpha larvae (Daoulas et al. 1993), and may benefit from the presence of Dreissenids that are already established in the Great Lakes (Benson et al. 2021). Occasionally it feeds on planktonic organisms. It is likely that this species will find an appropriate food source in the Great Lakes. Larger fish in the Great Lakes may prey on Knipowitschia caucasica but it is unknown whether that would prevent establishment. In the Aral Sea, it is one of the most abundant fish and is not a very important component of the diets of piscivorous fish (Baimov 1963). In contrast, it was found in only 0.6% of 767 sites in Hungary, with a relative abundance of 0.004% (Takács et al. 2017). It is unknown whether prastism will prevent the  establishment of Knipowitschia caucasica. Knipowitschia caucasica is a host to the parasites Aphalloides coelomicola, Cryptocotyle spp., Paratimonia gobii, Timoniella imbutiforme, Dichelyne minutus (Krasnoyd et al. 2012), Gyrodactylus bubyri, and Contracacaeum sp. (Stoyanov et al. 2015, 2016, 2018); however, there is currently insufficient information to determine if these parasites negatively impact the health of Knipowitschia caucasica, or its chances of establishing in the Great Lakes. Aphalloides coelomicola reduces the female gonad weight of the common goby (Pomatoschistus microps) (Pampouli et al. 1999). There is no evidence that Aphalloides coelomicola, Cryptocotyle spp., or Paratimonia gobii currently occur in the Great Lakes. Timoniella spp. has been found in the Great Lakes and reduces the ruffe’s (Gymnocephalus cernua) ability to survive in low oxygen waters (Pronin et al. 1997). Dichelyne spp. is reported to occur in the St. Lawrence River, but its occurrence and infection of native fish is low, and has not infected the nonindigenous round goby (Gendron et al. 2012).

Knipowitschia caucasica reproduces from the end of April to the end of July in the northern hemisphere at water temperatures of 15–27°C (Kevrekidis et al. 1990). The Great Lakes basin contains a number of areas that have appropriate spawning temperatures during those months. Knipowitschia caucasica has a slightly lower fecundity than other fish in the Knipowitschia genus. Its lowest reported fecundity is 60 eggs (Kevrekidis et al. 1990) and its highest reported fecundity is 1389 eggs (Gheorghiev 1964). Knipowitschia longecaudata has a fecundity of 350–2045 eggs (Zelenin and Vladimirov 1975; Ragimov 1986), and K. iljini has a fecundity of 2240 eggs (Ragimov 1986). In the Caspian Sea, Knipowitschia caucasica had a moderate relative fecundity relative to the other Knipowitschia gobies.

Currently, there is no evidence indicating that Knipowitschia caucasica would outcompete other species in the Great Lakes if introduced. There was some dietary overlap in Lake Egirdir between Knipowitschia caucasica and Atherina boyeri and A. anatoliae, however,  there did not appear to be competition as none of their respective populations were negatively impacted (Güçlü and Erdogan 2017). Its widespread distribution elsewhere has been attributed to its tolerance to a wide variety of environmental conditions, its non-specific diet, and early maturation (Kevrekidis et al. 1990). This species occurs in Lake Egirdir, Lake Eber, and Demirköprü, and is speculated to have been introduced by anthropogenic means due to this fish’s inability to cross hydroelectric dams to migrate up strong currents from the Asku River (Van Neer et al. 1999). No specimens of Knipowitschia caucasica were found in these lakes prior to 1992, but were abundant in Lake Egirdirby 1996, and were found in Lake Eber in 1997 and Demirköprü Dam Lake in 1998. There is a possibility that Knipowitschia caucasica was unintentionally introduced in these lakes with the stocking of common carp fry from Ipsala/Edirne hatcheries, which are located in the same region where this species is common. Kolar and Lodge (2002) predict that Knipowitschia caucasica may spread quickly after introduction using their models that take into account the fish’s growth rate, lower survival in high water temperatures, and tolerance of a wide temperature range. Further, Knipowitschia caucasica spread rapidly downstream the Tisca River basin from Romania (Antal et al. 2015) and from Tisza Lake to Csongrad, Hungary at 85 km/year (Harka et al. 2015a). After its introduction into the Carpathian Basin in Hungary in 2009, it spread to Serbia within 6 years, surpassing expectations of its potential distribution (Harka et al. 2015b).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Beneficial

Knipowitschia caucasica is host to the following parasites: Aphalloides spp. (Stoyanov et al. 2015), Gyrodactylys bubyri (Stoyanov et al. 2016), Paratimonia gobii and Contracacaeum sp. (Stoyanov et al. 2018), Cryptocotyle spp., Timoniella imbutiforme, and Dichelyne minutus (Krasnoyd et al. 2012). Knipowitschia caucasica had low parasite infection rates compared to native fishes in Hungary,  which may have contributed to their invasion success (Antal et al. 2015). There is no evidence that suggests that Knipowitschia caucasica poses a threat to native species or outcompetes native species for resources. There are no reports on how it affects or interacts with other species. This species does not degrade water quality or alter physical components of the ecosystem.

There is little or no evidence to support that Knipowitschia caucasica has the potential for significant socio-economic impacts if introduced to the Great Lakes.

There is no evidence that Knipowitschia caucasica poses a threat to human health or water quality, and that this species negatively impacts infrastructure, economic sectors, recreational activities and associated tourism, or the aesthetic appeal of the areas it inhabits.

There is little or no evidence to support that Knipowitschia caucasica has the potential for significant beneficial impacts if introduced to the Great Lakes.

It is unknown whether Knipowitschia caucasica can act as a biological control agent. Dressenid mussel larvae are part of their diet (Daoulas et al. 1993), but it is unknown whether this will significantly control dressenid populations. It is not known to be commercially, recreationally, or medically valuable. This species does not improve water quality or have positive ecological impacts.

There are no known regulations for this species.*

*Ballast water regulations applicable to this species are currently in place to prevent the introduction of nonindigenous species to the Great Lakes via shipping. See Title 33: Code of Federal Regulations, Part 151, Subparts C and D (33 CFR 151 C) for the most recent federal ballast water regulations applying to the Great Lakes and Hudson River.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control

Biological
There are no known biological control methods for this species.

Physical
There are no known physical control methods for this species.

Chemical
There are no known chemical control methods specific to this species. General piscicides (such as rotenone) may be used for control, but expect significant kill of non-target species.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.