The occurrence of M74 syndrome in female Atlantic salmon, Salmo salar L., belonging to two populations returning to spawn in Polish rivers in the fall of 2004 and three from pond cultivation were investigated. Eggs from total of 218 female specimens were investigated from rivers in northern Poland (80 – Darłowo, 72 – Miastko, 66 – Świbno). The study method applied involved comparing the concentrations in eggs of red (astaxanthin, canthaxanthin) and yellow (lutein, zeaxanthin) carotenoids. The specific carotenoids were determined with column chromatography (CC), thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The eggs of the investigated female Atlantic salmon were divided into three groups according in color: yellow, yellow-orange, and orange. Fifteen carotenoids were identified in the investigated Atlantic salmon females. Red carotenoids dominated in orange and yellow-orange eggs, while yellow ones dominated in yellow eggs. M74 syndrome was identified in 36 females, which represented 16.5% of all the investigated Atlantic salmon females.

Salmonid fishes represent an important component of the fisheries in Poland as well as in other countries. The stocks of salmonid fish in the natural waters depend to a large extent on the feeding conditions of the streams into which their larvae or fry are released. Rearing the fry on artificial diets prior to stocking, in a controlled environment, leads to a higher stocking success, primarily due to better survival rates compared with the free swimming fry. There is a hypothesis, however, that rearing the sea trout fry on a natural diet in the form zooplankton could considerably improve the chance of survival in the stream. Natural diets, contrary to the artificial ones, enhance the fry hunting instincts, which may often become a critical survival factor. This report presents the results of rearing sea trout fry on natural diets, which has been compared with artificial feeding as well. The food reservoir comprised the zooplankton collected from the outlets of an artificial and a natural water body.

The objective of the present work was to examine the length and weight growth rates. The sample was collected in June 1995 in the area between the Puck Bay and open waters of the Gulf of Gdańsk. Age of the individuals examined was determined from otoliths. Growth rates were estimated with back calculations. The length – weight relationship was estimated using the exponential function, whereas the weight growth rate was calculated with the modified von Bertalanffy equation. The fish examined aged from 1+ to 4+. The von Bertalanffy equation developed for calculating length growth is as follows: L_t = 14.61 [1–e^{-0.44756(t-0.0176)}], the total length – weight relationship can be expressed as W = 0.00985 Tl^2.5041, the weight growth rate estimated according to the modified von Bertalanffy equation is W_t= 8.13[1–e^{-0.44756(t-0.0176)}]^2.5041. The length growth rate is the smallest in the fish from the Gulf of Gdańsk, when compared to the samples from the North Sea. The weight growth rate of the sandeel studied is considerably lower, than that of the sandeel from the Pomeranian Bay.