Agata Korzelecka-Orkisz

Early ontogenesis of the angelfish, Pterophyllum scalare Schultze, 1823 (Cichlidae)

This study describes the egg membrane structures of angelfish (Pterophyllum scalare), morpho-physiological changes during angelfish embryogenesis from activation to hatching under optimal conditions (28°C; pH 6.8), the developing larvae and fry, the effect of alkaline pH on the early developmental stages of the species, the relationship between food item size and fry survival. Egg membranes (thin, transparent, 1.67-2.18 µm thick) are covered by a sticky substance. The amber-coloured angelfish eggs were oval in shape, with average diameters of 1.436 and 1.171 mm, i.e., a mean volume of 1.033 ± 0.095 mm3. The survival rate of embryos and larvae kept in water with an elevated, slightly alkaline pH was very low: as few as 2% of the embryos survived, while in the batch kept in optimal water conditions very few eggs died. The first larvae hatched after 1288 h of embryonic development. The newly hatched larvae measured on average 2.60 ± 0.093 mm and had large (0.64 ± 0.077 mm3) yolk sacs. They attached themselves to the substrate with a secretion of thin, viscous threads, which was released from glands situated on the top of the head. The glands vanished on day 5. The 1-day-old larvae showed the first pigment cells on the body and the eyes of the 2-day-olds were already fully pigmented. Between day 4 and 5 of larval life, the larvae began feeding on live food. The 23-day-old fry looked like a miniature versions of the adults. Mortality of the angelfish larvae during their first days after hatching was higher in those fed brine shrimp (Artemia salina) nauplii than those fed protozoans and rotifers.

The effect of static magnetic field on Danube huchen, Hucho hucho (L.) sperm motility parameters

Abstract The distribution range of Danube huchen, Hucho hucho (L.) in Polish waters is decreasing, and is currently only 25 to 30% of its original area. Since few data are available concerning Danube huchen, it is necessary to develop a better understanding of its reproduction to improve artificial spawning in hatcheries. Eight sperm motility parameters were assessed using CASA after short-term storage in a static magnetic field. The effect of magnetic field exposure on spermatozoa at fertilization and on sperm morphology (SEM) was also examined. Static magnetic fields had a positive effect on sperm motility parameters, including VCL, which determines fertilization effectiveness; values for this parameter after a 24 h exposure period to fields of different intensity were as follows: 1 mT - 110.09 μm s-1; 5 mT - 111.65 μm s-1; 10 mT - 152.10 μm s-1; control - 102.09 μm s-1. Egg fertilization rates of spermatozoa held for 24 hours in fields of 1mT was 71.32%, 5mT - 58.23%, and 10mT - 59.99%, and in the control - 32.60%. The mean length of spermatozoa was 27.14 ±0.22 μm; the head was elongate; length without the neck was 2.80 ±0.19 μm; the width was 2.0 ±0.08 μm. This study suggests that the method of exposing sperm to magnetic fields might, after more extensive studies, could be used for short-term sperm storage.

Peculiarities of embryonic development of round goby Neogobius melanostomus (Gobiidae) in fresh water

The results obtained indicate the potential of the round goby to reproduce in fresh water, which may result in further expansion of the species to upper reaches of rivers and to other water bodies (lakes, dam reservoirs). Embryonic development of the round goby in fresh water proceeded in a regular manner. However, embryonic development in fresh water took a shorter time than in saline water. Although the newly hatched larvae were somewhat smaller than those hatching from eggs kept in saline water, the hatching rate was high (90%). If the species finds conditions suitable for reproduction in Polish freshwater bodies, it may pose a threat to numerous native freshwater fish species by taking over both their feeding and reproductive niches.

The structure and the embryogenetic role of eggs and egg membranes of Ancistrus dolichopterus (Actinopterygii: Siluriformes: Loricariidae)

Genus Ancistrus is represented by fish commonly known as bushymouth or bristlenose plecos. They occur in the watershed of upper Amazon including Peruvian Ucayali and less frequently in the lower Amazon watershed (Kornobis 1990). The fish of this genus living in the wild can reach up to 15 cm of length, whereas in the captivity (culture) they do not exceed 13 cm (Riehl and Baensch 1996). Adults show sexual dimorphism, the juveniles look the same despite their sex. The reproduction of bushymouth catfish, Ancistrus dolichopterus Kner, 1854, is difficult to observe because it occurs at night in shaded areas—most frequently in hiding spots. The male prepares so called “pseudo-nest” before female would lay the eggs. He carefully cleans the nest and protects it from invasion of any potential predators e.g., snails. This specific care fulfilled only by the male lasts during the entire embryonic development till the larvae leave the nest, move independently, and are able to feed themselves (Rymkiewicz 1988). ACTA ICHTHYOLOGICA ET PISCATORIA (2011) 41 (3): 223–227 DOI: 10.3750/AIP2011.41.3.10