Stone Moroko
Description
Stone moroko is an alien species that belongs to the Cyprinidae - carp family. It was introduced into the Prespa Lakes in the 1970’s. It has an elongate body, slightly flattened on sides, resembling that of the species of the genus Gobio. It has a maximum size of up to 110 mm, though most individuals are 80-90 mm in length and 17.1-19.2 g in weight. The life span is up to 3-4 years. The head is somewhat flattened in its anterior part. The mouth is clearly in the top position. The dorsal and anal fins are short. The caudal fin is large and deeply incised, with both parts of similar size. The ventral fins are located slightly anterior to the dorsal fin. The throat is covered with scales. The lateral line is complete, running in the middle of the sides. The scales are large and cycloidal. The number of scales in the lateral line are (34) 35-38 (39). The coloration is similar in both sexes, with grey back, light sides and belly, passing from yellowish-green to silver. Young individuals have a dark stripe along the body sides; it disappears with age. In the caudal part of the scales the pigment forms characteristic lunate spots. The fins are pale, light yellow, only on the dorsal fin there is a darker stripe, running obliquely backwards.
Biology
It is zooplanktivorous fish and found in a wide variety of habitats, most abundantly in well vegetated small channels, ponds and small lakes. Adults are found in cool running water. They feed on small insects, fish and fish eggs, and plant material and usually breed in habitats with still or very slow-flowing water. It is regarded as a pest which competes with the fry of other species due to its high reproductive rate. The sexual dimorphism becomes pronounced during spawning. In males breeding tubercles appear on the head. The greatest accumulation of sharp tubercles is located in the anterior part of the head, on the front, near the nostrils and below and above the eye. Few tubercles are observed on the lower lip. In that period the males darken distinctly and their fins become black while the operculum gets violet. The females become clearly lighter. Spawning takes place when 1 year old. In the Amur River basin - Asia (its origin) the spawning starts when the water reaches the temperature of 15-190C (May-August), whereas in Europe it spawns earlier – in April-June. It can produce from a few hundred to a few thousand eggs. The spawning is multi-litter and takes place in the littoral zone. The eggs are laid on plants, sand, stones, mollusc shells and other substrata. Before spawning the female carefully cleans the substratum for egg-laying. During one act it lays up to several dozen eggs. One male may spawn with a few consecutive females. The male guards the eggs until hatching, and aggressively drives away other, often larger fishes.
Distribution
It is originally from Asia: Amur to Zhujiang drainages in Siberia, Korea and China. It was introduced to various areas in Europe and Asia. Several countries report adverse ecological impacts after introduction. In the Prespa Lakes it has been introduced by means of imported stocking material in the surrounding carp culture ponds.
Fishing significance
No.
Impact
In open waters it has probably contributed to a decrease in abundance or even disappearance of some autochthonous cyprinids.
Management
Stocking material imported for fish farms or in order to stock open waters should be carefully checked especially to ensure the absence of this invader. Additionally, using the stone moroco as live bait for predatory fish should be stopped.
