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.

The thyroid hormones (THs) play an important role in the regulation of the rate of metabolism, affect the growth and function of different systems in the organism. The aim of this study was to assess serum concentration of total triiodothyronine (T3), total thyroxine (T4) as well as T3/T4 ratio in serum from healthy fresh water fish from Salmonidae, Acipenseridae, Cyprinidae, and Clariidae families to determine species-specific reference intervals. Mean concentrations of T3 and T4 levels varied significantly among fish. Finally, the test results show clear differences in the serum concentration of the T3 and T4 and give new insight into the thyroid hormones reference values in some commercial fresh water fish species.

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.

The protective effects of herbal feed additives Withania somnifera, Silybum marianum, Centella asiatica, and silymarin (administered at feed levels of 4000 ppm, 5000 ppm, 4600 ppm, and 25,000 ppm, respectively) against the toxic effects of ochratoxin A (OTA) (administered at 2 ppm) were investigated in 48 New Zealand White rabbits (37 days old) over an 80-day experimental period. A decrease in body weight was seen in rabbits exposed to OTA alone, but that decrease was less pronounced in rabbits receiving herbal supplements. The most severe lesions in OTA-treated rabbits were found in the liver, kidneys and spleen, while milder lesions were seen in the heart, intestine and lungs. The intensity of macroscopic, histopathological and biochemical changes was highest in rabbits exposed to OTA alone, followed by rabbits additionally supplemented with herbal additives, as evidenced by histopathological findings and serum levels of blood urea nitrogen (BUN), creatinine, aspartate aminotransferase (AST), and alanine aminotransferase (ALT). The most pronounced protective effects of the herbal additives were observed in the kidneys and liver. Oxidative stress was significantly increased in rabbits exposed to OTA alone, as evidenced by elevated reactive oxygen species (ROS), nitric oxide (●NO), ascorbyl radicals (●Asc), protein oxidation (PO), procollagen type I alpha 1 (COL1A1), malondialdehyde (MDA), kidney injury molecule-1 (KIM-1), hydroxyproline (Hyp), advanced glycation end products (AEGs), heme oxygenase-1 (HO-1), catalase (CAT), and 8-hydroxy-2′-deoxyguanosine (8-OHdG), as well decreased superoxide dismutase (SOD) and glutathione peroxidase-1 (GPx-1) activities, while protective effects were seen for all herbal additives, and better expressed for Centella asiatica and Silybum marianum.