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Fish welfare has become a significant concern during the last decade. The issue of slaughter is getting the interest of many consumer organizations and fish growers, and suppliers. We need to take careful consideration to food fish slaughtering, and not only for an ethical reason. Numerous quality traits are in place already at the end of fish life. Nonetheless, other traits can be developed while the post mortem muscles are turning into consumer produce. Therefore, it is necessary to investigate ways to avoid the suffering of the fish before their processing. To improve the efficiency of the immobilizing and stunning process of the fish at the entrance of the fish plant, we investigated the use of CO2 in combination with low temperature. When combining CO2 to 2°C water temperature, fish were stunned and permanently immobilized within 20 min or less, while their core temperature was 3°C. Our results suggest that combining low temperature and bubbling CO2 in the fish receiving tank of the processing plant might be more appropriate for animal welfare. Therefore, we suggest continuing our experiments in the fish processing plant.

We present field observation results from October 2019 to February 2021 in Israeli fish farms. Surprisingly, two metazoan parasites, the larvae of Contracaecum multipapillatum and unidentified metacercaria N1, which disappeared from Israeli fish farming 30 years ago, were commonly found in the current study. The reappearance of these two helminths is likely related to changes in the management policy related to new regulations regarding bird-of-prey species. It means that farmers could have prevented parasitic infections by keeping away piscivorous birds from their fish ponds and by treating these ponds with appropriate compounds against the affected invertebrates.

In this study we examined the physiological responses of different strains of gilthead sea bream (Sparus aurata) to chronic and acute stress factors. Blood glucose levels, hematocrit, and lactate concentrations were examined in yearlings of different strains of gilthead sea bream subjected to different stress situations. In the first experiment, fish of the Ardag and ‘ebony’ strains were kept 45 days in moderate (35-45 kg/m3) or high (70-90 kg/m3) density. There were no significant effects on the blood glucose level but, at both densities, hematocrit was significantly higher in the Ardag strain (33.2±3.0% at moderate and 44.5±1.6% at high) than in the ebony strain (22.0±3.0% and 19.9±2.7%, respectively). The interaction of ‘strain’ and ‘crowding’ was highly significant, suggesting that hematocrit may respond differently in each strain to crowding. In the second experiment, we examined the effects of acute stress (handling without anesthesia) among four strains representing Mendelian mutations that affect body coloration in gilthead sea bream: ebony, ‘white’, ‘yellow’, and the normally pigmented Ardag. Significant variations in the glucose and lactate concentrations suggest that genotypes of gilthead sea bream may have heritable differences in their physiological responses to stress factors.

One of the major problems in the mariculture of the commercially important European sea bass, Dicentrarchus labrax, is that females grow 20-50% more rapidly than males. For that reason, farmers are interested in developing female monosex populations. Studies on evolution, genet- ics, and physiology have been conducted during the last decade to solve this problem. This review summarizes the latest data related to the effects of evolution, genetics, physiology, and environment on sex determination and differentiation in the European sea bass.

The melatonin-generating system of the European sea bass, Dicentrarchus labrax, was studied in vitro using a perfusion tissue culture methodology. The examined properties included photic entrainment in the pineal gland, and circadian rhythmicity in alternating dark and light, in contin- uous darkness, and in continuous light. Pineal glands were removed from adult fish and placed in a perfusion tissue culture at a constant temperature of 24°C. Melatonin discharge into the cul- ture medium was measured using radioimmunoassay. Melatonin concentrations during a pho- toperiod of 12h light:12h dark were low during the light periods and high during the dark. The melatonin discharge was inhibited by continuous light but strong and rhythmic in continuous dark with a circadian period (Tau) of about 24 h (n = 10). The results demonstrate that the European sea bass pineal gland is photosensitive, with ability to be entrained, and contains an internal cir- cadian oscillator that regulates melatonin production.

The natural habitat of the white grouper, Epinephelus aeneus, is the Mediterranean Sea, which has a salinity of approximately 35 ppt. As fish species vary in their tolerance of environmental conditions, potential production in specific conditions must be determined empirically. The growth, survival and cortisol level of 1.7 g grouper juveniles grown in diluted sea water (4 ppt) or brackish water (4 ppt) from the Tsofar well in the Arava (southeastern Negev, Israel) was com- pared to the growth of similar fish in sea water (43 ppt). Survival in all treatments was 100%. During the first ten days, the fish grown in brackish water grew significantly less (p