Diel changeover of fish assemblages in shallow sandy habitats of lowland rivers of different sizes

Diel dynamics of species richness and fish abundance were studied in three lowland rivers that differed significantly in size (discharge) in to the upper Vistula River drainage system (Poland). Shallow sandy habitats at point bars were repeatedly sampled with beach seining over 24-h periods. Species richness peaked at dusk and then decreased throughout the 24-h period in all the rivers. Overall fish abundance changed similarly in the smallest and the largest river, whereas in the mid-sized river it increased in the late afternoon hours. Some species (three gudgeon species, golden loach, and chub) were persistently nocturnal, whereas others (dace, bleak, and roach) shifted to diurnal activity in the mid-sized and large rivers. These differences in diel changes in the abundance of certain species might be explained in the context of variation in availability (i.e., proximity) of other, more heterogeneous habitats

Ex situ protection of the European mudminnow (Umbra krameri Walbaum, 1792): Spawning substrate preference for larvae rearing under controlled conditions

Captive breeding programs of endangered fish species, such as the European mudminnow Umbra krameri, are essential for population restoration. To improve captive spawning and larvae rearing under controlled conditions, two experiments were carried out. In the first, the spawning substrate preference was tested in triplicate, where five different types of artificial surface were provided for mudminnow pairs:(i)sand, (ii)artificial plants, (iii)gravel, (iv)sand + artificial plants and(v)gravel + artificial plants. All fish preferred the gravel + artificial plant combination, which indicates that this type of surface could be the most appropriate for spawning in captivity. In the second trial, three feeding protocols were tested in triplicate under controlled conditions. In the first treatment fish were fed exclusively with Artemia nauplii; in the second treatment fish were fed with Artemiafor the first ten days then Artemia was gradually replaced with dry feed; for the third group the transition period started after 5 days of Artemia feeding. Although the survival rate of larvae could be maintained at a high level in some of the feeding protocols, a strong decrease in the growth rate was obvious in all diets containing dry food, which means that live food is essential for the first three weeks of mudminnow larvae rearing