BACKGROUND: Sex determination is an essential issue in certain fish species, like sturgeons. During the rearing management, distinguishing between male and female fish is an important process for producing meat or caviar.OBJECTIVES: The current study aimed to find the feasibility of electric organ discharge (EOD) frequency ‎generating to introduce a novel method of sex determination in three freshwater species, namely the ‎black ghost knife fish (Aptronotus albifrons), goldfish (Carassius auratus), and the Sterlet ‎sturgeon (Acipenser ruthenus), as non-electric fishes.METHODS: In this regard, following sex detection, EOD frequency ‎of fishes were recorded via an oscilloscope. In addition, knife fish was used as a reference sample on which a lot of work has been done to evaluate the accuracy of the method and the use of the oscilloscope. Furthermore, the EOD frequency of male and female ‎Sterlet sturgeons was recorded and reported for the first time in this study.RESULTS: The frequency ‎magnitude was significantly different in genders of Sterlet (P<0.05) with higher EOD frequency in males ‎than in females. There was no recorded frequency in goldfish ‎male and female. EOD frequencies, which were recorded in male and female of black ghost fish, ‎represented significant differences compared with the other studies (P<0.05).CONCLUSIONS: The results achieved ‎in this study revealed that sex differences are one of the effective parameters in terms of EOD ‎frequency inequality; this non-invasive method can be utilized for sex identification of valuable ‎species, like sturgeon. However, it is required to gather advanced equipment and conduct further ‎research in physiology and biology of reproduction for accurate recording of electrical frequencies ‎and detection of their origins.

The aim of this article was to evaluate the influence and effects of chosen bioaccumulative substances i.e. heavy metals, pesticides, and polychlorinated biphenyls (PCBs) on fish, as well as provide information on time trends and potential threat to human health. Chemical substances which pollute water may affect living organisms in two ways. First of all, large amounts of chemical substances may cause sudden death of a significant part of the population of farmed fish, without symptoms (i.e. during breakdown of factories or industrial sewage leaks). However, more frequently, chemical substances accumulate in tissues of living organisms affecting them chronically. Heavy metals, pesticides, and polychlorinated biphenyls are persistent substances with a long-lasting biodegradation process. In a water environment they usually accumulate in sediments, which makes them resistant to biodegradation processes induced by, e.g., the UV light. These substances enter the fish through direct consumption of contaminated water or by contact with skin and gills. Symptoms of intoxication with heavy metals, pesticides, and PCBs may vary and depend on the concentration and bioavailability of these substances, physicochemical parameters of water, and the fish itself.

Nontuberculous mycobacteria (NTM) are increasingly recognised as causative agents of opportunistic infections in humans for which effective treatment is challenging. There is very little information on the prevalence of NTM drug resistance in Poland. This study was aimed to evaluate the susceptibility to antibiotics of NTM, originally isolated from diseased ornamental fish.

Histamine is one of the most important and toxic biogenic amines which may be present in food and may cause food poisoning in humans when contained at a high level. It is produced during bacterial decarboxylation of histidine in fish muscles. The aim of the study was to investigate the presence of histamine in fish and fish products available in Poland during 2014–2018.

Introduction: In the present study, some of the commercial fish farms located in the Black Sea region of Turkey, were screened for bacteria between 2012 and 2014.

In freshwater fish with external fertilization, sperm sampling can be contaminated with urine, which triggers motility and gives rise to decreased fertilization success. The maintenance of freshwater fish in hyperosmotic conditions may reduce urine production and improve sperm quality. Thus, the aim of this work was to verify if acute exposure to various NaCl concentrations improves sperm quality in the yellowtail tetra Astyanax altiparanae. Spermiation was induced using a single dose of carp pituitary gland (5 mg kg-1) and the males were maintained at various NaCl concentrations: NaCl 0.00% (control), NaCl 0.45% (hypoosmotic), NaCl 0.9% (isosmotic) and NaCl 1.0% (hyperosmotic) for 6 h at 26 °C. Sperm was collected and verified for activation by urine and motility traits. At 0.00%, 0.45%, and 0.90%, the sperm was motile just after sampling, indicating activation by urine. Surprisingly, at hyperosmotic conditions, no activation was observed. Other sperm and motility parameters did not show any statistical differences, including sperm viability (P = 0.7083), concentration (P = 0.9030), total motility (P = 0.6149), VCL (curvilinear velocity; P = 0.1216), VAP (average path velocity; P = 0.1231) and VSL (straight-line velocity; P = 0.1340). Our results indicate that acute maintenance at hyperosmotic conditions eliminates sperm activation by urine and maintains sperm quality. Such a new procedure is interesting for both basic and applied sciences, including reproductive practice in fish.

A field study was carried out in a fish farm to study the effect of seasonal variations during the production period on performance and parasitic infestation of cultured fish. Water samples were obtained to determine the Physio-chemical investigation of water in the examined farm to estimate temperature, dissolved oxygen, PH, ammonia, nitrite, nitrate, salinity, total alkalinity and total hardness. Fish samples were obtained for parasitological examination to detect external parasitic infestation.The results referred that an elevation of water temperature during summer months leading to slight increase of PH of water, while dissolved oxygen values decreased from 6.8±0.15 to 6.0±1.5 throughout the study period. The mean values of ammonia, nitrite and nitrate reach the maximum in July and August months (0.71±0.18, 0.20±0.07 and 3.1±0.07 mg/l respectively). In addition there was a slightly increase of the total alkalinity and total hardness at beginning of the study (37.8±3.0 and 147.0±5.0mg/l respectively) reached the maximum levels in the summer months (44.4±2.8 and 182.8±6.0 mg/l respectively). It can be noticed that the most prevalent ectoparasitic affecting cultured Tilapia are Trichodina,Monogenia and Epistylis. It can be noticed that, the average initial body weight of examined fish was 6.8±2.3 gm and reached 218.0±3.8 gm. at the end of experiment (210 days) with an average of daily weight gain 1.01 ±0.07 gm. From the aforementioned results, it can be concluded that special attention to Physio-chemical parameters of water fish ponds and regular inspection of fish parasitic infestation particularly during summer months obtained a good fish performance as well as high body weight gain and high survival percentage.

A study was conducted to investigate the antibacterial activities of allicin, one of the major essential oils of garlic, against some fish pathogenic bacteria as well as the toxic effect of allicin on monosex Nile tilapia (Oreochromis niloticus). Allicin 10% v/v solution in dimethyl sulfoxide (DMSO) was used in this study. The bacterial species investigated were Aeromonas hydrophila, A. caviae, A. sobria, A. veronii, and Streptococcus iniae. The minimum inhibitory concentrations (MICs) of allicin in DMSO against Aeromonas hydrophila was found to be 125 μg/mL, while ranged between 250–500 μg/mL for each of A. caviae, A. sobria, A. veronii. Interestingly, the MIC for Streptococcus iniae was 63 μg/mL. On contrary, allicin exists no bactericidal activity against any of the investigated bacteria. Allicin had high toxic effect on tilapia fingerlings while adult tilapia could tolerate it.

This study was carried out to evaluate the bacteriological status of fresh Tilapia nilotica, fresh Clarias lazera, frozen Mackerel and smoked Herring fish marketed in Beni-Suef City. The collected samples were examined for total bacterial count, coli form (MPN), faecal coli forms (MPN), E. coli (MPN), Staphylococcus aureus count, total proteolytic count, total lipolytic count, Aeromonas count and Pseudomonas count, as well as the isolation of E. coli, Staphylococcus aureus, Aeromonas hydrophila, Pseudomonas aeruginosa, Yersinia enterocolitica and Listeria monocytogenes. Most of the examined samples were within the permissible limits recommended by EOS and ICMSF, few samples of fresh Clarias lazera exceeded the recommended limits. The economic importance and public health significance of the isolated organisms were discussed.

A total of one hundred samples of marketed fish farm; 25each of tilapia (Oreochromis niloticus), Mugil cephalus, Carp (Silver) and fry; were collected from different localities at Al- Behera and Kafr El-Shakh Provinces. The samples were examined for detection of testosterone hormone by Thin Layer chromatography (TLC) as well as it was quantitatively assayed by Radio-Immuno-Assay (RIA). The obtained result revealed that the testosterone residues were detected in flesh of farm fish of Tilapia (Oreochromis nilotocus) and Carp (Silver), each constituting 24% and 4 %; respectively but it could be failed to detect in each of Mugil cephalus and fry. The hormonal residues of testosterone was ranged from 3.25 to 34.9 ng/g with mean value 4.22±1.1 ng/g in positive samples of Tilapia, while only one sample of Carp showed 22.0 ng/g, Mugil cephalus and Fry showed no detectable level of hormonal residues. The public health significance of detectable levels was discussed as well as the recommendations to avoid health hazards from such fish were mentioned.