Removal of dead fish eggs by Asellus aquaticus as a potential biological control in aquaculture.

The objective of the present experimental study was to gain a better understanding of the foraging activity of Asellus aquaticus during fish egg incubation. A. aquaticus were introduced into experimental setups of dead eggs, viable eggs and hatched larvae of zebrafish (Danio rerio), a commonly used model organism. The amount of A. aquaticus and the duration of their exposure to the eggs significantly affected the proportion of consumed dead eggs in each experimental cycle. A. aquaticus belongs to the group of aquatic detritivores, and no predatory behavior was observed during the experiments. These crustaceans could distinguish between the dead eggs and those containing living embryos. Furthermore, zebrafish larvae remained unharmed by A. aquaticus, even in the absence of alternative food source. These findings underscore the potential sanitary role of these crustaceans in natural waters and offer new perspectives on their possible use as biological control organisms in aquaculture hatcheries. Additionally, our results suggest a potential application of A. aquaticus in combating pathogens by reducing the growth substrates for bacteria and fungi.

The growth performance of pond-reared common carp (Cyprinus carpio) larvae propagated using cryopreserved sperm.

The aim of our study was to determine the efficacy of utilizing cryopreserved common carp sperm (in comparison to fresh sperm) for propagation at a Hungarian aquaculture facility. The sperm was frozen in 5 mL straws using an extender method that was previously tested in common carp. Sperm motility was monitored using a computer-assisted sperm analysis system. The hatching and malformation rates among the specimens were recorded before the stocking of larvae in both groups. The growth (body weight, total length) and survival rates of the fish were measured during the pre-nursing (from May to June: between 1 and 26 days post hatching) and grow-out periods (from June to October: between 26 and 105 days post hatching) of the same year. The fresh sperm, which was collected and pooled prior to fertilization, showed high MOT (97%), pMOT (92%), VCL (106 µm s-1), LIN (75%), and ALH (1.84 µm). Prior to the fertilization trial of the cryopreserved sperm, low MOT (34%), pMOT (14%), and VCL (61 µm s-1) values were observed in frozen-thawed sperm. A significantly higher hatching rate was measured in the fresh sperm group (87%) when compared to the cryopreserved sperm group (42%). No significant difference in the overall malformation rate was observed in larvae originating from either the fresh or frozen sperm. A significant difference between the two test groups was observed in the incidence of deformed tails (fresh: 20%, cryopreserved: 55%). Except for one sampling period, no significant difference in the body weight and total length of the fish larvae was found between the two groups throughout the pre-nursing and grow-out periods. A significantly higher larvae survival rate was noted in the fresh sperm (72%) as compared to the cryopreserved group (43%) by the end of the pre-nursing stage. However, no significant difference in survival rate was observed for the cryopreserved sperm (96%) in comparison to the fresh sperm (95%) by the end of the grow-out stage. The results of this study showed, for the first time in large-scale pond culturing, an equal growth and viability in larvae propagated from cryopreserved sperm when compared to fresh sperm (despite the limited available rearing ponds provided by the commercial company).

Chronic Effects of Carbamazepine, Progesterone and Their Mixtures at Environmentally Relevant Concentrations on Biochemical Markers of Zebrafish (Danio rerio).

The impact of pharmaceuticals on non-target organisms in the environment is of increasing concern and study. Pharmaceuticals and other pollutants are often present as mixtures in an environmental compartment. Studies on the toxicological implications of these drugs on fish, particularly as mixtures at environmentally relevant concentrations, are very limited. Thus, this study aimed to evaluate the chronic effects of the anticonvulsant drug carbamazepine (CBZ) and progesterone (P4) at environmentally relevant concentrations, individually and in binary mixtures, applying a suite of biomarkers at the molecular level in zebrafish (Danio rerio). The effects on biotransformation enzymes 7-ethoxyresorufin O-deethylase (EROD) and glutathione-S-transferase (GST), antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), glutathione peroxidases (GPxSe and GPxTOT), and glutathione reductase (GR), and markers of damage, such as DNA strand breaks (DNAsb), lactate dehydrogenase (LDH), lipid peroxidation (LPO), and vitellogenin-like proteins (VTG), were evaluated. Analyses of the biochemical markers indicated that a synergistic dose-ratio-dependent effect of CBZ and P4 in zebrafish occurs after chronic exposure regarding VTG, biotransformation enzymes (EROD, GST), and oxidative stress marker (DNAsb). The results suggest a synergistic effect regarding VTG, thus indicating a high risk to the reproductive success of fish if these pharmaceuticals co-occur.

Biochemical Marker Assessment of Chronic Carbamazepine Exposure at Environmentally Relevant Concentrations in Juvenile Common Carp (Cyprinus carpio).

Worldwide, the anticonvulsant drug carbamazepine (CBZ) is the most frequently identified pharmaceutical residue detected in rivers. Reported chronic effects of CBZ in non-target freshwater organisms, particularly fish, include oxidative stress and damage to liver tissues. Studies on CBZ effects in fish are mostly limited to zebrafish and rainbow trout studies. Furthermore, there are only a few chronic CBZ studies using near environmental concentrations. In this study, we provide data on subacute effects of CBZ exposure (28 days) to common carp (Cyprinus carpio), employing a set of biochemical markers of damage and exposure. CBZ was found to induce a significant change in the hepatic antioxidant status of fish subjected to 5 µg/L. Moreover, with increasing concentrations, enzymatic and non-enzymatic biomarkers of oxidative defence (catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), DNA strand breaks)), toxicant biotransformation (ethoxyresorufin-o-demethylase (EROD), glutathione-S-transferase (GST)), and organ and tissue damage (lactate dehydrogenase (LDH), cetylcholinesterase (AChE)) were altered. The AChE, LDH, and lipid peroxidation (LPO) results indicate the occurrence of apoptotic process activation and tissue damage after 28 days of exposure to CBZ. These findings suggest significant adverse effects of CBZ exposure to common carp at concentrations often found in surface waters.

Comparison Evaluation of the Biological Effects of Sterigmatocystin and Aflatoxin B1 Utilizing SOS-Chromotest and a Novel Zebrafish (Danio rerio) Embryo Microinjection Method.

Aflatoxin B1 (AFB1) is a potent mycotoxin and natural carcinogen. The primary producers of AFB1 are Aspergillus flavus and A. parasiticus. Sterigmatocystin (STC), another mycotoxin, shares its biosynthetic pathway with aflatoxins. While there are abundant data on the biological effects of AFB1, STC is not well characterised. According to published data, AFB1 is more harmful to biological systems than STC. It has been suggested that STC is about one-tenth as potent a mutagen as AFB1 as measured by the Ames test. In this research, the biological effects of S9 rat liver homogenate-activated and non-activated STC and AFB1 were compared using two different biomonitoring systems, SOS-Chromotest and a recently developed microinjection zebrafish embryo method. When comparing the treatments, activated STC caused the highest mortality and number of DNA strand breaks across all injected volumes. Based on the E. coli SOS-Chromotest, the two toxins exerted the same genotoxicities. Moreover, according to the newly developed zebrafish microinjection method, STC appeared more toxic than AFB1. The scarce information correlating AFB1 and STC toxicity suggests that AFB1 is a more potent genotoxin than STC. Our findings contradict this assumption and illustrate the need for more complex biomonitoring systems for mycotoxin risk assessment.

The effect of two different experimental rearing temperatures on the quality and the large-scale cryopreservation of Eurasian perch (Perca fluviatilis) sperm.

Eurasian perch is an important fish species for European aquaculture diversification, but the quality of reproduction still remains one of the main limitations for further industry development. In particular, the optimal condition to obtain the best quality of sperm is poorly understood. The aim of our study was to measure the possible effects of two experimental rearing temperatures (6 °C and the conventionally used 12 °C) and of hormonal stimulation, on the motility parameters (pMOT, VCL, VSL, LIN, ALH, BCF), osmolality and fertilizing capacity of Eurasian perch sperm at the end of the reproductive cycle. A prior untested, large-scale (5 mL cryotube and Polystyrene box) cryopreservation method was implemented using fresh sperm obtained from the two above mentioned temperature groups. Males were injected with 100 µg body weight kg-1 sGnRHa. No significant difference was recorded between the two rearing temperatures and between the saline control and sGnRHa treated groups on the different features of sperm quality. A similar fertilization rate was monitored in all sGnRHa treated (6 °C: 69 ± 13%, 12 °C: 81 ± 11%) and saline control groups (6 °C: 79 ± 10%, 12 °C: 87 ± 4%). Correspondingly, no significant difference in hatching rate was observed in the sGnRHa injected (6 °C: 27 ± 9%, 12 °C: 40 ± 20%) and saline control (6 °C: 35 ± 18%, 12 °C: 36 ± 7%) males. However, a notable negative effect of freezing process on sperm movement was observed following thawing in both temperature groups. No significant difference in the motility parameters was measured between the two temperature groups following large-scale cryopreservation. Furthermore, a similar result was observed in the fertilizing capacity (6 °C: 79 ± 10%, 12 °C: 75 ± 8) of thawed sperm as well as in the hatching rate (6 °C: 52 ± 13%, 12 °C: 46 ± 19%). Our results indicate that fresh Eurasian perch sperm can tolerate a reduced rearing temperature following hormonal treatment. The adopted large-scale cryopreservation method could be used efficiently in the future for the fertilization of large amounts of Eurasian perch eggs following a precise standardization process.

Parvularcula mediterranea sp. nov., isolated from marine plastic debris from Zakynthos Island, Greece.

A Gram-negative, dark orange-pigmented, aerobic, non-spore-forming, coccoid-shaped bacterium designated as ZS-1/3T was isolated from a floating plastic litter (polypropylene straw) sample, collected from shallow seawater near the public beach of Laganas on Zakynthos island, Greece. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolate is affiliated with the genus Parvularcula in the family Parvularculaceae. Its closest relatives are Parvularcula lutaonensis (98.09  %) and Parvularcula oceanus (95.89  %). The pH and temperature ranges for growth are pH 5-10 and 20-38 °C (optima, pH 7.0 and 28 °C). The predominant fatty acids are C18 : 1 ω7c (56.84  %), C16 : 0 (27.51  %), C18 : 0 (2.25  %) and C12 : 0 (1.42  %). The predominant respiratory quinone detected in strain ZS-1/3T is quinone-10 (Q10); the majority of detected polar lipids are glycolipid. The DNA G+C content is 62.5  mol%. Physiological and chemotaxonomic data further confirmed the distinctiveness of strain ZS-1/3T from other members of the genus Parvularcula. Thus, strain ZS-1/3T is considered to represent a novel species of the genus, for which the name Parvularcula mediterranea. sp. nov. is proposed. The type strain is ZS-1/3T (=NCAIM B 02654T=CCM 9032T).