This is the first report of the early development for the endemic Krbava minnow Delminichthys krbavensis from a karstic field in Croatia, and the first report of any species of the genus Delminichthys. The description is based on basic morphometric measures and meristic counts during a 48-day observation of embryos and larvae acquired from successful spawning and rearing in an aquarium. The mean total length of larvae at the time of hatching was 3.12 mm. Mouth opening and independent feeding and intestinal function were observed after day 11 post-hatching (PH) at which time the yolk sac was completely absorbed in all individuals. Flexion of the urostyle began after day 18 PH and was completed by day 23 PH. Pectoral fins developed on day 7 PH, pelvic fins begin to develop by day 44 PH and the formation of caudal, dorsal and anal fin was complete by day 48 PH, when individuals presented the full set of soft rays. Understanding its early development is particularly valuable in assessing the environmental impacts on this endangered species and is essential for its effective monitoring and conservation.

This paper aims to establish how Telestes karsticus has adapted its reproductive behaviour to the hydrological conditions in Sušik Creek, which dries up in the summer. Initial data are provided on the reproductive biology of this endangered (EN) and endemic species of Croatia. Fish were collected at monthly intervals from July 2007 to July 2008 using a backpack electrofishing device. The spawning period lasts from late March to early May, confirmed by the gonadosomatic index (GSI) of males and egg diameter measurements. The value of GSI for both males and females is clearly cyclic, with only one maximum achieved in April. Sexual maturity is reached at an early age, with 50% becoming mature at total lengths longer than 41 mm (males) and 51 mm (females). Absolute fecundity of gravid females ranged from 201 to 3,188 eggs and relative fecundity was 153.6 ± 33.9 eggs per gram of body mass. Average egg diameter was determined as 1.22 ± 0.23 mm. The species is lithophilous, with eggs found in nature on gravel and among rocks. Water temperature during the spawning period ranged from 7.3°C to 13.5°C, with an average of 9.8°C. The spawning period coincides with the second peak of the 30-year-average water level in the creek, which runs dry during the summer period.

The genus Aulopyge, represented by a single species, the Dalmatian barbelgudgeon, Aulopyge huegelii, is an endemic genus with very restricted distribution range comprising several rivers in southern Croatia and Bosnia and Herzegovina. In this study, molecular genetic analyses based on three molecular markers (one nuclear and two mitochondrial) were performed to confirm the position of Aulopyge within Cyprinidae, obtain data on its evolutionary history, and describe its population genetic structure and diversity. Specimens of A. huegelii were obtained throughout the distribution range. Phylogenetic reconstruction corroborated the independent position of this species and its placement within the Barbinae subfamily. The evolutionary history of A. huegelii started already in the middle Oligocene, whereas intraspecific divergences that left a trace in its current genetic structure and diversity are of much younger origin, starting in the middle Pleistocene. Unlike in other cypriniform species and genera distributed in the Dinaric karst region, there is no significant structuring within A. huegelii, or distribution of haplotypes concordant with the geographic scale. Furthermore, low effective population sizes estimated for most populations and low genetic diversities within them raise strong concerns about the viability and future survival of this endemic species.