No abstract

The paper presents the results of investigations on the feeding of bream larvae reared in illuminated cages in a mesotrophic lake. The same species of zooplankton were found in both the lake and the fish cages. Copepoda predominated in abundance and biomass. During the mixed feeding the bream larvae diet consisted of rotifers (45.8%), small cladocerans (41.6%) and phytoplankton (13.6%). According to Ivlev's selectivity indices (E), the most important food species were: Keratella cochlearis, and Chydorus sphaericus (E ¼ +0.88). The total length (TL) of bream larvae consuming their first nauplii and copepodites of Copepoda was 8.9 mm. As bream larvae grew, cladocerans were more often selected than rotifers. Copepods usually made up an insignificant component of the diet. Bream larvae in illuminated cages generally fed at night; their alimentary tracts were filled to the maximum in the period from sunset to sunrise. Indices thereof reached 755.6 at night and 278.0 in the daytime.

The aim of the study was to describe the peculiarities of pike spawning in mesotrophic Lake Rubikiai, to determine the spawning population structure and evaluate the influence of some environmental factors on year-class strength formation. The data were collected in April and May (1994–2011). A total of 1586 individuals were caught. The age of pike ranged from 1 to 12 years; 2–5-yearold males (96.0%) and 3–8-year-old females (89.1%) prevailed. The overall sex ratio of females to males was 1:4.1. One-year-old spawning males (26.5–28.5 cm) and two-year-old spawning females (31.5–35.5 cm) constituted 2.1% and 2.6%, respectively. Water temperature during the spawning period was relatively stable, between 4 and 6°C, during March and increased slightly towards 10°C in the middle of April. No correlation was observed between female length and spawning date. Year-class strength did not correlate with the last day of ice presence and the minimal water level at the end of spawning (WLmin), but statistically significantly negatively correlated with the maximum water level at the beginning of spawning (WLmax) and the difference between WLmax and WLmin. The mean annual survival rate for pike (aged ≥2) was 0.74 and the mean annual instantaneous mortality rate was 0.45.

The aim of the study was to determine the growth rate and growth parameters of pike Esox lucius L. in the mesotrophic Lake Rubikiai and to evaluate species growth in light of environmental conditions in Lithuanian lakes of different limnologic types. A total of 204 pike specimens were caught in two subsequent years, April 2005 and April 2006, in Lake Rubikiai. Six age classes (2-7 years of age) for males and 10 age classes (3-12 years of age) for females were identified by scale readings; 2-to 4-year-old males and 4-to 7-year-old females prevailed. Total length of pike ranged from 26.5 to 107 cm and weight from 106 to 7600 g. There were no statistically significant differences (StudentÕs t-test, P > 0.1) between mean lengths and weights of males and females of the same age. Von Bertalanffy growth parameters for the entire population were: L ¥ = 131.7 cm, k = 0.1530 year )1 , t o = )0.0398 year. Calculated overall growth performance index u¢ was 3.42. The length-weight relationship was described by the equation W ¼ 0:0060 Â L 3:0167 . The growth rate of pike in Lake Rubikiai was higher than in most other investigated Lithuanian lakes. Pike from Lake Rubikiai are characterized by average growth, compared to other populations from various geographical locations. No significant differences were established between the growth of pike in mesotrophic and eutrophic lakes. Pike growth rate did not correlate with lake surface area, maximum or mean depth, and negatively correlated with bogginess in mesotrophic lakes and limpidity and bogginess in eutrophic lakes (P < 0.05).

The current paper is a survey of fish passes built in Lithuania and a generalisation of the data on their efficiency collected during the period 19981999. At the present time, there are 11 fish passes in Lithuania, two of which are fish locks, three pool and orifice fish passes, three pool and weir fish passes, one Denil fish pass and two bay-pass channels. Two fish passes are at a standstill because of some technical faults. Three fish passes operate inefficiently. According to the data collected in 1998 1999, before the reconstruction, Tauragë fish lock provided a passageway for about 9% of vimba and 15% of sea trout, which had gathered at the dam during their spawning migration in autumn. In 1998 about 460 vimba and 220 sea trout ascended upstream through this fish pass, whereas in 1999 their number was 430 and 150 respectively. Through the fish pass of Anykðèiai, only local spring spawners can get into their spawning grounds, since migratory fish species (vimba, sea trout, salmon, river lamprey) ascending upstream to spawn are stopped by the Kavarskas dam situated downstream of Anykðèiai.