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The aim of the presented study was testing the efficacy of an herbal concoction in goldfish (Carassius auratus) experimentally infected with Aeromonas hydrophila. After an intramuscular injection of the pathogen, the scales sloughed off on the site of the injection, with an appearance of a muscular haemorrhagic protuberance, which progressed into an extensive ulcerative dermatitis associated with focal haemorrhage, oedema, and dermal necrosis exposing the underlying muscle. The progression of the disease affected organs in the following order: muscle, gills, liver, and finally the heart. The dip treatment with the 1% herbal concoction for 5 min daily restored the macro- and microscopical structure of the altered primary gill lamellae, liver, heart, and muscles. The recovery changes were described.
To assess the current ecosystem status of Montedoglio Reservoir and surrounding waters, the fish fauna has been analysed in 1993, about five years after the first experimental impoundment. Total number of 898 fishes of fifteen species have been collected of the total biomass of 117 kg. The most abundant species were pumpkinseed (Lepomis gibbosus), goldfish (Carassius auratus L.), bleak (Alburnus alburnus alborella De Fil.), largemouth bass (Micropterus salmoides Lac.), rudd (Scardinius erythrophthalmus L.), and chub (Leuciscus cephalus L.), while the three: Carp (Cyprinus carpio L.), goldfish, and largemouth bass accounted for the most biomass. Of the most common species, carp, chub, largemouth bass and rudd provided insight into population structure and growth. In 1992, a year of heavy spring rains and a rapid water exchange, a year-class abundance across all species was particularly poor. The results of water levels and outflows between 1992-1994 showed a high degree of instability of the system. It appeared to favour fish species depositing their eggs inshore (i.e. chub) and predators (i.e. largemouth bass), while species with life stages feeding on plankton or benthos were not favoured.
The 96 h LC50 values of copper for Carassius auratus and Xiphophorus helleri were 0.30 and 0.36 ppm. Sublethal concentrations of copper affected specific growth rate and reproductive performance in both species. Metal accumulation in muscle and gonad tissues was linearly increased with increase in sublethal levels of copper and exposure period. Young ones accumulated same or more amount of metal found in gonad tissue of parent fish and it might be due to the direct transfer of copper from gonad to young ones during development. Metal accumulation caused significant (P<0.05) reduction in mean diameter and weight of eggs in C. auratus and mean body length and weight of fry in X. helleri. Ovo-viviparous fish is more severely affected by copper toxicity than oviparous fish.
Fishery and aquaculture play an enormous role in reducing poverty and alleviating food insecurity at household level. The first fish stocking program in Ethiopia was reported as early as 1925. Indigenous Oreochromis niloticus, Tilapia zilli, Clarias gariepinus and non-native Cyprinus carpio, Carassius carassius, Carassius auratus, Ctenopharyngodon idella and Salmo trutta fish species were used for stocking. Even though most of the fishery enhancement programs are low-cost operations, they often seem to be very efficient actions. Fish harvested in the reservoirs Fincha and Amerti in Oromia region, lakes Haik and Ardibo in Amhara region and Hashengie in Tigray region, enhanced by stocking, contribute up to 15% of the annual fish production of the country. Thus fisheries programs challenging the growing protein-rich food demand should be considered as a necessary and valuable aspect of management strategy in all waters, independently from its major operational goal like hydropower or irrigation.
Experiments were conducted to document behavioural responses of koi carp, Cyprinus carpio L., and goldfish, Carassius auratus (L.) to monoculture and polyculture conditions in aquaria. Two parallel experiments, otherwise involving similar experimental protocols, were carried out with two batches of fish, fed with live tubifex worm (first batch) and live zooplankton (second batch). Each of the trials, randomized with respect to treatment, yielded data on aggressive encounters (chases, nips), both in presence and absence of food. The two species exhibited considerable variation in the extent and type of aggression displayed, koi carp being the more aggressive species. Frequency of attack increased in the presence of food. The impact of aggressive behaviour of koi carp was conspicuous by the increased level of attack on goldfish in polyculture trials in both experimental batches.
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