ISSN 00329452, Journal of Ichthyology, 2009, Vol. 49, No. 5, pp. 383–389. © Pleiades Publishing, Ltd., 2009. Original Russian Text © A.N. Pashkov, D.D. Zvorykin, 2009, published in Voprosy Ikhtiologii, 2009, Vol. 49, No. 3, pp. 396–401.
Some Morphoecological Specific Features of Cichlasoma Rocio octofasciata (Perciformes, Cichlidae) from the Population in Lake Staraya Kuban A. N. Pashkova, D. D. Zvorykinb a b
Kuban State University (KubGU), Krasnodar, Russia
Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences (IPEE RAN), Leninskii pr. 33, Moscow,119071 Russia * Email:
[email protected] Received March, 12, 2008
Abstract—Results of studies of cichlasoma Rocio octofasciata, a new species for Russia that naturalized in Lake Staraya Kuban (the city of Krasnodar) are presented. Estimates of the main meristic characteristics of the fish and a description of its coloration, as well as data on the feeding of cichlasomas in the lake and values of several most important morphofunctional characteristics of the studied fish are provided. Causes of natu ralization of the studied population and perspectives of its existence are discussed. DOI: 10.1134/S003294520905004X Key words: @,
Previously we (Zvorykin and Pashkov, 2008) reported the finding of an allochtonous species— cichlosoma Rocio octofasciata—new for Russia. The American cichlid fish has been inhabiting Lake Staraya Kuban (the city of Krasnodar) for over 25 years and has become so numerous that it serves as an item of amateur fishery. Despite this, R. octofasciata has not been included into any regional report on ichthyo fauna up to now (Moskul, 1998; Plotnikov, 2000; Emtyl' and Ivanenko, Ivanenko, 2002; et al.). It was first mentioned in scientific literature only at the beginning of the 21st century (Pashkov et al., 2004, 2005), and its species qualification has been estasb lished only quite recently (Zvorykin and Pashkov, 2008). Studies of the population of this species, alien for Lake Staraya Kuban, are at an initial stage; however, the data we obtained up to the present allow us to state that this species has completely naturalized in the water body: it formed a selfreproducing and rather numerous population. Over two years of studies we revealed several specific features of the ecology of R. octofasciata in the lake, which suggested several considerations with regard to the place of this species in the lake biocenosis and perspectives for the develop ment of its population. Besides our own data, we also analyzed and considered data on the biology of this eurybiontic cichlid fish in its natural range and outside it (Zvorykin and Pashkov, 2008).
The purpose of this investigation was to study the main morphological and morphofunctional charac teristics, as well as specific features of the feeding and habitat conditions of the population of R. octofasciata from Lake Staraya Kuban. MATERIAL AND METHODS The study was performed on 20 specimens of R. octofasciata: five of them were caught with fishing rods in August 2003 and 15 were caught with a gill net in September 2006. We used the scheme of measurements and conven tional designations used for the description of the morphology of Perciformes by Smirnov (1986) with regard to the recommendations for performing this procedure in respect to cychlids (Barel et al., 1977). All counts of meristic characteristics were performed on the left side of the fish by one operator. Total (TL) and standard (SL) lengths of the fish body and the number of spiny and soft rays were determined, as well as the total number of rays in dorsal, (D), anal (A), ventral (V), and pectoral (P) fins and number of perfo rated scales in upper (ll1) and lower (ll2) branches of the lateral line. Unsegmented and unbranched rays were assigned to spiny rays and segmented and branched rays were assigned to soft rays. Pectoral fins of some specimens had segmented but unbranched rays; when measuring them they were assigned to soft
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Krasnodar
ray
aK
ub a
n
Warm arm
La
ke
Sta
Cold arm
Kuban River
Figure. Scheme of Lake Staraya Kuban.
rays. If fins included rays fused for most part of their length, they were taken for one ray. The biological analysis and study of feeding were performed according to standard methods (Pravdin, 1966; Borutskii, 1974; Vol’skis et al., 1976) on the 15 specimens caught in September 2006. Body weight (Q), weight without entrails (q), and weight of liver and intracavity fat were determined; the sex of the specimen, maturity stage, and weight of gonads were identified; indices of fatness and liver were calculated; gastrointestinal content was also determined. The data obtained were processed using standard methods of variation statistics. For assessing habitat conditions of the population of R. octofasciata, the chemical water composition and the temperature conditions of Lake Staraya Kuban were studied. Analysis of the chemical composition of water samples taken in 2003 and 2006 was performed in the laboratory of the Biotechnology Center of Kuban State University. Water temperature dynamics was studied from November 2006 to the beginning of May 2007. Measurements were performed weekly at a depth of approximately 0.5 m: one point in the cold arm of the lake and three points in the warm arm at a distance of 250, 500, and 1000 m from the site of dis charge of waters of the Krasnodar Heat and Electric Power Plant. Temperature was recorded using electron thermometer Checktemp within an accuracy of 0.1°C.
RESULTS AND DISCUSSION Habitat conditions. Lake Staraya Kuban, located in the vicinity of the city of Krasnodar, is an oxbow lake of the Kuban River (figure). At the present time, the water body is used as a cooling water body of the Kras nodar Heat and Electric Power Plant as well as for rec reation and fish cultural purposes. The lake consists of eastern (cold) and western (warm) arms separated by a dam. Water intake for the Heat and Electric Power Plant is performed from the cold arm and the pro cessed warm water is discharged into the warm arm. The lake in the southern part is connected with the Kuban River by a system of locks. The area of the water body is slightly larger than 3 km2. Depths are comparatively small and water areas for the most part do not exceed 2.0–2.5 m, the maxi mum depth is 4.5 m. The ground is mainly siltysandy; there are some snagged sites and those covered with construction rubbish. Most part of the lake is covered with submerged and semisubmerged aquatic vegeta tion. Freezing in the western arm is lacking, and in the eastern arm is observed only in some most severe win ters. The lake is characterized by thermal conditions, atypical for other water bodies of the region, deter mined by the discharge in the western arm of warm waters of the Heat and Electric Power Plant. The most JOURNAL OF ICHTHYOLOGY
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warmed site is located in the western arm near the site of the discharge of warmed waters. Farther, in the direction of the Kuban River, water temperature grad ually decreases. In the period from November 2006 to April 2007, water temperature in the western arm at a distance of 250 m from the site of discharge fluctuated in the range of 19.0–26.0°C, at 500 m it ranged from 18.2–23.5°C, and at 1000 m it ranged from 17–23°C. In the eastern (cold) part of the lake, water tempera ture in the same period varied in the range of 7.5– 17.5°C. Water chemical composition in the lake was char acterized by the following values of the main indices: pH 6.85–7.23, hardness 3.55–10.40 mmol/l, per manganate oxidation 2.91–9.25 mg O2/l, nitrites 0.03–1.00 mg/l, nitrates 1.01–11.11 mg/l, ammo nium nitrogen 0.04–0.40 mg/l, total phosphorus 0.01–0.04 mg/l. An analysis of the main hydrological characteristics of the lake demonstrates that they are sufficiently favorable for the naturalization of R. octofasciata. It is known (Konings, 1989; Page, Burr, 1991; Obordo and Chapman, 1997) that this species prefers biotopes with large amounts of aquatic vegetation and soft grounds, is undemanding with respect to water chemical com position and the size of a water body, and can endure very low oxygen concentrations in water. The lethal water temperature determined experimentally is 8°C (Shafland and Pestrak, 1982). Structural indices of ichthyocenoses existing in the lake also possibly favor the development of a popula tion of R. octofasciata. Experimental seinings made with fry tuck net showed that the values of indices such as the total number of species, number of species per unit of area, fish density and Margalef index in the warm part of the water body are considerably lower than in the cold part. This can be regarded as evidence of the disturbance of the ichthyocenosis of the warm arm, which, as is known, increases the possibility of a successful introduction (Shvarts et al., 1993). The combination of factors such as the thermoph ication of waters, the impoverishment of ichthyo cenoses, and the activities of a fish farm, in which sev eral species of tilapia and common bullhead Ictalurus punctatus were cultivated led to the fact that the ich thyofauna of Lake Staraya Kuban is characterized by the highest diversity of transcontinental invaders in the Northwestern Caucasus. Representatives of North American, South American, and African ichthyofau nas (common bullhead Ictalurus punctatus, mosquito fish Gambusia holbrooki, tilapia Oreochromis aureus, and cichlasoma R. octofasciata) have naturalized in it (Pashkov et al., 2004, 2005; Zvorykin and Pashkov, 2008); cases of catch of guppy Poecilia reticulata and Mozambique tilapia O. mossambicus are known (Plot nikov, 2000; Emtyl’ and Ivanenko, 2002). Fish coloration. The intravital background colora tion of studied fish varies from grayolive to dark blue JOURNAL OF ICHTHYOLOGY
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green. The general coloration background of fixed specimens is violetgray; in larger fish, violet shade is manifested more strongly. Specific features of colora tion are 8–11 dark vertical stripes running along the body and extending to the fish’s head. These stripes are seen most distinctly in preserved fish of any size. Intravital coloration masks them partially: in some adult fish, stripes are noticeable only on the forehead and on the back. The species is characterized by two clearly noticeable dark spots: one of them is located on the middle part of the body, and the second is on the upper part of the caudal peduncle. In live specimens, they look like ocellate spots. The dorsal fin has a red boundary. The orbital envelope is gray with a bronze shade. Gill covers, unpaired fins, and the body are covered with numerous small iridescent spots. Color ation corresponds to the description of typical colora tion of this species of cichlid fish available in literature (Konings, 1989; Page and Burr, 1991; Conkel, 1993). Morphological characteristics. In studying and analyzing morphological characteristics of the popu lation of R. oscifasciata from Lake Staraya Kuban, we encounted a paradoxical situation. On the one hand, this is a widely distributed species, and the fact that it is undemanding allowed it to populate various water bodies (up to roadside trenches) both within its natural range and far beyond it. In particular, this species that originates from fresh water bodies of the Atlantic slope of Central America was recorded in the United States, Australia, and Thailand (Welcomme, 1988; Page and Burr, 1991). This is one of the popular model items widely used in various biological studies, including behavioral (Baerends, Baerends van Roon, 1950), his tological (Sire, 1988), and physiological (Bell, 1981). Finally, it is one of the most popular aquarium cichlid fish; it has been known to Russian aquarists since the beginning of the 20th century (Il’in, 1965). On the other hand, it appeared that the taxonomic position of this species has remained doubtful until now, and the data on its morphology, including those on meristic characteristics important for taxonomy are extremely scarce. The initial description made in the beginning of the 20th century (Regan, 1903), as well as modern field keys (Page, Burr, 1991), and taxonomic reports (Kullander, 2003) contain minimal information. Estimates of the main meristic characteristics in fish of the population studied by us are listed in Table 1. The fin formulas are: D XVII–XIX 9–11, A VII–IX 8–10, V I 5, P 12–14. The number of perforated scales in ll1 is 11–21 (more frequently, 17–19) and in ll2 is 5–11. A singlefactor dispersion analysis performed for each characteristic demonstrated that the size varia tion of most meristic characteristics is not pro nounced. A statistically significant relation between standard body length and the characteristic value was revealed for only one of 12 analyzed characteristics— the number of perforated scales in the lower branch of the lateral line (F = 7.31, p = 0.006). Therefore, con
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Tаble 1. Body length and meristic characteristics of Rocio octofasciata from the population in Lake Staraya Kuban (n = 20 specimens) Characteristic values Characteristic SL, mm TL, mm Total number of rays in D Number of spiny rays in D Number of soft rays in D Total number of rays in A Number of spiny rays in A Number of soft rays in A Total number of rays in V Number of rigid rays in V Number of soft rays in V Number of soft rays in P ll1 ll2
min–max
M±m
38–106 49–135 27–30 17–19 9–11 16–18 7–9 8–10 6 1 5 12–14 11–21 5–11
57 ± 4.2 72 ± 5.1 28.1 ± 0.15 18.1 ± 0.12 9.9 ± 0.14 17.1 ± 0.12 8.3 ± 0.13 8.8 ± 0.12 6.0 ± 0.00 1.0 ± 0.00 5.0 ± 0.00 13.6 ± 0.13 17.8 ± 0.47 8.7 ± 0.50
Here and in Table 3: min–max is the minimal and maximum values of the characteristic; M ± m is the average value of the characteristic and its standard error.
Таble 2. Number of rays in dorsal and anal fins of Rocio octo fasciata Lake Staraya North and Central America Kuban Page and Schmitter (our data) Burr, 1991 Soto, 2007 Number of spiny 17–19 17–19 17–19 rays in D Number of soft 9–11 9–10 8–10 rays in D Number of spiny 7–9 8–9 8–9 rays in A Number of soft 8–10 7–8 7–9 rays in A Characteristic
Таble 3. Main morphofunctional characteristics of Rocio octo fasciata from the population in Lake Staraya Kuban Characteristic SL, mm Q, g q, g Fatness index, % Liver index, %
Characteristic value
n, specimens
min–max
M±m
20 20 15 15 15
38–106 2.0–45.8 1.9–29.2 0.2–2.1 0.4–3.8
57 ± 4.2 9.8 ± 2.54 6.6 ± 1.93 0.9 ± 0.25 1.7 ± 0.25
sidering the lack of size dynamics of meristic charac teristics, the data obtained can be regarded as repre sentative for the whole population, despite the small amount of studied fish (SL 38–106 mm at an average value 57 ± 4.0 mm). The relation between the number of perforated scales in the lower branch of the lateral
line and fish size requires additional study. It is likely that during ontogenesis, an increase in the number of perforated scales occurs in specimens of the studied population. Note that the obtained estimates of the number of rays in the dorsal and anal fins slightly differ from those cited in literature; however, the latter also differ. Table 2 lists the results of our studies and data from two publi cations (Page and Burr, 1991; SchmitterSoto, 2007). The presence of complete coincidences and certain misinterpretations is obvious. There can be several causes for such discrepancies, for instance, the geo graphic variation of the species, the effect of the founder or the subjectivity of the operator who counts. Species identification of fish. Because of the men tioned scarcity and discrepancy of data on the taxon omy and morphology of R. octofasciata, the determi nation of the species of cichlid fish of the studied pop ulation is an independent task. Their belonging to cichlids of the New World causes is not doubted thanks to the rather typical habitus and the combination of key characteristics of these fish (Konings, 1989; Conkel, 1993). It also became obvious that the fish do not belong to the genus of acaras Aequidens, to which they were initially supposedly related. First of all, this is evidenced by the scalecovered insertions of dorsal and anal fins, as well as by a high number of spiny rays in the dorsal and especially the anal fins (Kullander, 2006). These characteristics indicate the relation of fish to a group of cichlosomas, closely related to acaras, that consists of several genera of American cichlids. Specific features of coloration together with morphometric data permitted us to distinguish these fish from zebra cichlid Amatitlania nigrofasciata and other closely related species and identify them as Rocio octofasciata. Morphofunctional indices of fish. Of 15 dissected fish, 13 turned out to be juvenile and two were mature. The values of several morphofunctional characteristics of the studied fish are presented in Table 3. The length (SL) of juvenile fish varied from 38 to 59 mm with an average value of 47 ± 1.5 mm; body weight varied from 2–9 (average of 4.5 ± 0.41) g. One of the mature fish was male and the other was female. The male had an SL of 81 mm and a body weight of 21.6 g; its gonads were at maturity stage II, the gonadosomatic index (GSI) was low (0.46%). The female had an SL of 90 mm and a weight of 34 g; its gonads, despite the time of catch (end of September), were very well developed (maturity stage IV, GSI = 3.83%). In the gonads, 1010 rather large eggs of similar size were found; they can be considered to be a single batch. Note that, according to published data (Sakurai et al., 1993), the amount of one batch in this species does not usually exceed 800 eggs. The estimation of the relation between fish length (SL) and indices of fatness and liver demonstrated that the fish length significantly affects only the latter JOURNAL OF ICHTHYOLOGY
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Таble 4. Indices of feeding of Rocio octofasciata from the population in Lake Staraya Kuban (n = 15 specimens) Content of food components
Food component and other indices
specimens, %
%
33 1 1 1 1 5 3 9 ? ?
61.1 1.9 1.9 1.9 1.9 9.3 5.6 16.7 ? ? 52 ± 3.8 7.6 ± 0.22 0.6 ± 0.28 1.3 ± 0.25 2
Midges Chironomidae, larvae Caddis flies Trichoptera, larvae Dragonflies Odonata, larvae Ants Formicoidea, imago Beetles Coleoptera, imago Other aerial insects Insecta, imago Mollusks Gastropoda Sunflower seeds Helianthus annuus Moss animalcules Bryozoa, @фрагменты Invertebrata, @икра SL, mm Q, g Average index of stomach fullness, % Average index of intestine fullness, % Number of empty digestive tracts, items
Frequency of occurrence, % 13 7 7 7 7 33 13 33 7 7
Note: “?” means that the component was found as fragments or cannot be counted for some other reasons.
index; with an increase in the fish size, the liver index also increases (F = 4.60, p = 0.033). Specific features of feeding. An analysis of gas trointestinal content in fish indicates the active feed ing of all studied fish specimens (Table 4). Food includes plant and animal components at a quantita tive domination of the latter. According to the fre quency of the occurrence among animal components, aerial insects dominated while larvae of midges (Chi ronomidae) dominated quantitatively. Food also included aquatic larvae of other insects, gastropods of the genus Physa, eggs of aquatic invertebrates, and fragments of moss animalcules. Juvenile fish in food boluses of the studied specimens was lacking. Plant components accessible for identification were sunflower seeds used by local amateur fishermen as additional food for fish. This fact demonstrates a wide flexibility of the species which has adapted to use food that is not typical for it but is abundant and acces sible. CONCLUSIONS The problem of invasions of alien fish species is rather urgent for our country (Dgebuadze et al., 2002; Pavlov et al., 2003); however, several taxa, including the cichlid family, remain at the periphery of interest for specialists in this field. In our opinion, it should be considered that cichlids are among the most popular aquarium fish in our country. Millions of specimens of hundreds of cichlid species inhabit aquariums all over Russia. It is entirely impossible to assess how they for some reasons turn out to be in natural water bodies. An extremely high adaptive potential of many species of this family can allow them to adapt to new ecological JOURNAL OF ICHTHYOLOGY
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conditions and successfully compete with aboriginal species. For instance, on November 17, 2006, an adult specimen of O. aureus with a length of approximately 20 cm was caught in the watersupplying canal of the Adygei sturgeon fishcultural farm. The caught speci men likely belonged to the population of this species from Lake Staraya Kuban located 5 km downstream the Kuban River from the watersupplying canal. Water temperature at the site of the catching of tilapia was only 8°C. The fish was in a normal physiological state and, after catch, lived several weeks in one of the basins of the farm. R. octofasciata has also a high adaptive potential. It managed to inhabit water areas located considerably northward its natural range. For instance, in the 1970s, R. octofascia was first recorded as an alien species in water bodies of the United States. The first prognoses were pessimistic, the potential damage to aboriginal species and biocenoses, as a whole, following the introduction of this fish was assessed as rather high (Courtenay et al., 1974). It is true that the expected expansion did not occur. Local cichlosoma popula tions, on reaching comparatively small sizes, ceased to increase their numbers and occupied a rather modest position in ecosystems or disappeared altogether (Jen nings, 1986). At the present time, R. octofasciata is considered to be a species that presents no serious eco logical hazard for water bodies of the United States (Shafland, 1996). In Russia, the main factor that limits the distribu tion of R. octofasciata are undoubtedly temperature conditions. The available experimental data on threshold values of temperature for this species (Shafland and Pestrak, 1982) are as follows: a decrease in foraging activity at 16°C, cessation of feeding at
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13°C, loss of equilibrium at 9°C, and mortalityat, 8°C. It is obvious that in most water bodies of Russia in the winter period, temperature minimum will have values lethal for R. octofasciata. At the same time, Lake Staraya Kuban is not a single water body subjected to thermophication, and the possibility of the effect of R. octofasciata on similar biocenoses cannot be excluded without special studies. The prognosis for the subsequent existence of the population of R. octofasciata in Lake Staraya Kuban is a task of the future. Even a correct estimate of the potentially limiting environmental factors requires additional monitoring. Nevertheless, even now the fact of the naturalization of this species in the lake causes no doubts. Considering the frequency of its occurrence in catches of amateur fishermen, it may be suggested that many hundreds, if not thousands of specimens of various size and age were caught over the latest years. The estimation of the effect of R. octofas ciata on the lake ecosystem is possible only after an integrated study that includes the study of its feeding, reproduction, competitive relations with other fish, population dynamics, and other specific features of the biology of this species.
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