In the Bulgarian aquaculture sector, focusing research efforts on the technical specifications of the cultivation of African catfish (Clarias gariepinus) is important due to the need for more information. We aimed to assess the impact of light intensities on prolactin and cortisol levels as stress markers in African catfish. Fish were acclimated over an appropriate period to the short photoperiod (16D and 8L) and then distributed randomly to three groups, each separated by sex. Fish exposed to different light intensities (63, 51, and 40 lux, respectively) were followed for 45 days by lux meter. Blood samples were collected from the caudal vein using a 2 ml K2EDTA-coated syringe. A laser fluorescence reader assayed plasma prolactin and cortisol. The pituitary was removed from anesthetized fish and fixed for histological examinations. The results of our study suggest that increasing light intensity increases prolactin and cortisol levels in African catfish.

A pathobiome approach has been revealed as a set of organisms (i.e. prokaryotic, eukaryotic, and virus associations) in the aquatic environment that interact with the host (fish) to cause disease. The approach of the one pathogen–one disease is not wholly satisfactory to comment on the impairment of health status and disease process in fish. To exemplify the pathobiome concept, we present a fish disease in which more than one pathogen and possible synergistic interaction of inadequate water quality. In this case, the heavy mortalities were observed in Salema (Sarpa salpa) from an exhibition aquaria. Bacterial identification with matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI-TOF MS) showed the pathogen bacteria species of vibrio and photobacterium. In the parasitic examination, the invasion of marine ciliata, Cryptocaryon irritans was observed in the diseased fish. Moreover, poor water quality was considered as contributing factor to disease emergence in this case. The co-existence of pathogen Vibrio species (Vibrio harveyi) and Photobacterium damsela with its subspecies (subsp. damsela and subsp. piscicida) as well as marine ciliata, C. irritans for a description of a disease picture in a marine fish species are reported for the first time, providing an example of a pathobiome paradigm.

Although aggregation of macroparasites characterized by unequal distribution of parasites on the host is a known axiom in marine fishes, aggregation of nematode, Hysterothylacium aduncum was not previously studied in whiting, Merlangius merlangus. Here, we investigated the host-related (fish condition factor) and parasite-related factors (parasite load) as well as the distribution pattern of H. aduncum in whiting to determine whether aggregation existed or not. The distribution of H. aduncum (third larval stage) in whiting has been shown to be aggregated. Aggregation of H. aduncum was assessed by Weibull distribution. The aggregation degree of nematode, H. aduncum in whiting was changed by the individual fish. The observed pattern of parasite distribution by the individual fish enabled the recognition of aggregation for the first time in whiting. The prediction of the intensity of H. aduncum in whiting improved the understanding of the host-parasite system, particularly for the dynamics of the parasite.

The aim of the present investigation is to compare the effect of standard method and electrical stunning on some hemolymph biochemical parameters in mid-sized Red Swamp Crayfish. The results showed that electrical stunning time of induction was significantly shorter and recovery was longer than chilling stun. Parameters of an electrical field that stuns crayfish beyond the point of recovery without causing damage have been identified. Based on this experiment, it seems that electrical stunning would be preferable to the other method.

Aspirin is one of the most widely used medications globally as an analgesic and antipyretic drug. Aspirin use as an antiparasitic against fish parasites has never been tested. The parasite Dactylogyrus is considered a serious threat to freshwater aquaculture in relation to considerable losses. The present study is aimed to evaluate the antiparasitic effect of aspirin against Dactylogyrus extensus on Cyprinus carpio and alteration in gill histopathology. In vitro, aspirin exhibited antiparasitic activity with median effective concentration (EC50) values at one and six minutes of 8.137 g/L⁻¹ and 1.629 g/L⁻¹, were assessed for the first time. In vivo antiparasitic efficacy of aspirin to D. extensus was found to be 46.49%. Severe lesion profile was observed in histopathological evaluations of the gills.