Biological characteristics of sea trout smolts (Salmo trutta m. trutta L.) grown from fry released in the Stream Osówka

Abstract

In spring 1987 the fry of sea trout was introduced into the upstream of Os6wka Smolts grown from this material were caught during three successive years after the fish release, with the aid of fish trap situated in the middle course of the stream. Sex, condition and coefficient of gonads development, as well as length, weight and factor condition of smolts of the known age were determined. INlRODUCTION The :SUl'.Vivitl rate of juveniles of sea trout (Salmo trutta m. trutta L.) grown in Osowka lllreaJD-frPni. the introduction of fry to the downstream migration, appeared to be ea three u.nes higherJhan the survival rate of feeding larvae of sea trout till the period of descending [Chelkowski 1993]. Undoubtedly the biological characteristics of smolts grown in Osowka from the introg.u,ced fty ofknown age when comparing to the data given by Chelkowski [1990, 1992) concerniri.g sea. trout smolts grown in the same stream from the feeding larvae of as well bown age, could d� not only the cognitive but also practical value. The present paper is third in a series of studies on sea trout smolts grown in Osowka stream ftom the fty released [Chelkowski 1993, 1993a]. 20 Zygmunt Chelkowski ., MATERIAL AND }METHODS. ' Osowka is one of the small left-side tn"butaries of lower Odra river, having its source in Warszewskie Hills reaching-lJ.l m over the sea level No salntonids-were found in the indigenous ichthyofauna [Chelkowski 1993]. 3080 individuals of sea trout fry in the age of 10 weeks, at the mean length of30.7+o.66 mm and weight of281.6+5.66 g were released into the upper course of Osowka on 7 May, 1987 [Chelkowski 1993]. The fry was obtained from eggs of sea trout captured in the river Rega in autumn, 1986, being under incubation in the deep water, at constant temperature of 8°C. Next the fry was transferred to the rotary pond being swelling with' the same water and fed by dry drop-stuff till the day previous to the release [Trzebiatowski et al. 1992]. Smolts grown from this material were caught during their descent to the sea with the aid of fish trap located in the middle current of stream, working from the 1 March to 15 July 1988, 1989 and 1990, ie. in three successive years after the release. Smolts in Pomeranian J,ivers migrate 4ownstream in spring [Cbelkowski 1990; D1tbowski et al 1992], and their stay jn the river til l thq pimod of descent isili:mited from lt.o 3 years [Chrzan 1959; Dixon 1931; D�owski et al 1992]. Length (1 caud.) in mm and weight in g of gutted and non-gutted smolts (without the alimentary tract, heart, liver, milt and gonads) were estimated. Sex was determined from gonads; their development was established according to 8-stage Maier's scale [Meisner 1948]. Next the weight of gonads was recorded with the accuracy to 1 mg in order to calculate the coefficients of gonad maturity demonstrating the per cent ratio of

Age structure of the smolts of the migratory morphotype of the brown trout (Salmo trutta m. trutta L., 1758) from the Gowienica River

“…8). On the other hand the two-year-old smolts of the Os6wka (Chelkowski 1995) differed the most in this respect from the remaining smolts of the Rega (Chelkowski 1978) and Molstowa (36.6 g) (Chelkowski and Chelkowska 1982).…”

“…7) it is evident that the age structure of the smolts studied in the entire study period is very similar to the results obtained by Chelkowski (1978) for the Rega River. On the other hand, the age structure of the Gowienica smolts for the entire study period is dis tinctly different from the age structure of the smolts from the Os6wka River (Chelkowski 1992;1995) and from the Gnilna River (D�bowski and Radtke 1994). The age structure of the smolts from the Molstowa (Chelkowski and Chelkowska 1982) is the most similar to the structure of the season of 1980 of the present study (Tab.…”

“…9). Domagala (1986) * cited after Chelkowski (1978) Among the trout smolts mi gr ating down-stream in the Gowienica River as well as in other Pomeranian rivers there were more females than males (Chelkowski 1992(Chelkowski , 1995Chelkowski and Chelkowska 1982). It was similar for the adult trout on their spawning mi grations (Chelkowski and Domagala 1990).…”