Increase In Fishing Mortality Research Articles

Lactiplantibacillus plantarum fermented broth improved survival of marble goby (Oxyeleotris marmoratus) after skin abrasion by regulating skin mucus microbiota

Skin abrasion makes fish more susceptible to pathogen infections, which may cause a substantial increase in fish mortality. Hence, a 22-day trial was carried out to investigate the effect of Lactiplantibacillus plantarum fermented broth on the survival and microbiome regulation of marble goby (Oxyeleotris marmoratus) after skin abrasion. 135 fish (initial average weight, 3.39 ± 1.36 g) were divided into 9 tanks with triplicate treatment groups: control group (healthy fish), abraded group (skin abraded fish) and abraded &L. plantarum-treated group (skin abraded fish and 100 ppm L. plantarum fermented broth adding). The results showed that skin abrasion caused a 28.89% decrease in survival percentage of fish compared to the control group, whereas L. plantarum fermented broth significantly increased survival percentage by 44.45% when compared to the abraded group. Furthermore, skin abrasion reduced the diversity of bacterial and fungal communities in skin mucus and the abundance of Bacteroidetes phylum, Firmicutes phylum and Hydrogenophaga flava species, while increased the abundance of Aeromonas veronii and Cetobacterium somerae species. Nevertheless, L. plantarum treatment resulted in opposite results in fish, and it also increased the abundance of Lactobacillaceae family and potential bacterial and fungal probiotic species in gill and skin mucus. In conclusion, L. plantarum fermented broth may improve survival percentage of marble goby after abrasion by modulating the microbiota composition of fish skin mucus.

Fish mortality associated to volcanic eruptions in the Canary Islands

The Canary Islands are an active volcanic archipelago. In the last decade, volcanic activity has occurred twice on the youngest and western most islands: El Hierro (submarine eruption) in 2011-12, and La Palma (subaerial eruption) in 2021. 70 fish specimens of different species from El Hierro volcano and 14 from La Palma were necropsied. A notable high and early mortality of fishes was registered during the submarine eruption of El Hierro. In most of them, generalized congestion in the gills, liver, spleen, kidney, heart and rete mirabile of the swim bladder was observed. Some specimens also presented exophthalmia, gastric eversion, ocular haemorrhages, over-inflation of swim bladder and gas bubbles mainly on the skin and cornea. The eruption of La Palma volcano was characterized by the emission of large amounts of lava flows and pyroclastic deposits (mainly ash in size) both, on land and sea. Lava flowed on land and eventually reached the sea, forming lava deltas in the coastline of La Palma. This event was also associated with an increase in fish mortality in locations near to the lava deltas. Fishes presented ash particles in opercula/oral cavities and gills. In addition, several fishes presented an intense intestinal impaction composed of volcanic material including ashes and hyaloclastites fragments. To our best knowledge this study describes, for the first time, pathological findings in dead fishes associated with two different styles of recent volcanic eruptions in the Canary Islands.

Acute damage from the degradation of Ulva prolifera on the environmental microbiota, intestinal microbiota and transcriptome of Japanese flounder Paralichthys olivaceus

Green tide outbreaks caused by overgrowth of Ulva prolifera in the Yellow Sea of China can cause serious ecological stress with concomitant economic hardships, especially to marine fisheries. In this study, short-term effects (14 days) were evaluated using fresh algae U. prolifera (FU), and a 7-day assessment of the effects of decomposing U. prolifera (DU) algal effluent was conducted to determine the effects on the environmental and intestinal microbiota, intestinal transcriptome and mortality of the commercial marine benthic fish, Japanese flounder (Paralichthys olivaceus). The results revealed that algal degradation altered the microbial community structure of fish farm water and fish intestines and increased the relative abundance of the pathogens Flavobacteriaceae in water and Vibrio in fish intestines. Fish intestinal tissue structure appeared to be damaged, as indicated in pathological sections, and transcriptome analysis showed intestinal inflammation after exposure, which may have caused an increase in fish mortality. The degradation of U. prolifera led to a bloom of potential pathogenic bacteria and the inflammation of fish intestines, which resulted in disease in the flounder population that reduced fish harvests and might pose a potential health threat.

Cages’ farming foundation as a limiting factor in cultivation of sturgeon fish hybrids

The work experimentally confirmed the negative influence of fouling of cage structures on the growth and survival rates of reared young sturgeon hybrid — bester (Huso (Linnaeus, 1758) × Acipenser ruthenus (Linnaeus, 1758)). A significant decrease in growth and an increase in fish mortality in modules with a maximum biofouling area was noted. The possibility of using alternative cleaning methods in comparison with traditional mechanical and chemical ones has been investigated. The positive results of the experimental approbation of the author’s development — the practical application of a specially designed structure made of tarpaulin for the cage are given. The use of an easy-to-manufacture and operate device prevented active contamination of the cells, increased the efficiency of keeping fish, which is economically beneficial for commercial sturgeon growing in cages. In general, in fish farms located in a natural reservoir in the spring-summer period, the overgrowth of fodder bottoms and cage walls with filamentous algae has a strong negative effect on the cultivation of sturgeon fish. To optimize the fish-breeding process and reduce the number of algae during the period of their active growth on cages (the timing must be determined according to the conditions of a particular reservoir), special canvas covers should be used. This device will reduce the amount of sunlight entering the cage bottoms and slow down the growth of filamentous algae. To install this device on the cage, two workers are required, the approximate installation time (and, if necessary, dismantling) will be 20 minutes. To reduce the negative effect of algae fouling of the cage bed, measures should be taken to mechanically clean the stern bottoms and walls of the cage with high-pressure cleaning (washer) devices, after transplanting the cultivated objects into another fish hatchery

Acute Toxic Effects of Polyurethane Microplastics on Adult Zebra Fish (Danio Rerio)

Aim: Microplastics (MPs) have become an emerging environmental contaminant and there are increasing concerns about potentially toxic effects on living organisms. This study is aimed to determine uptake, tissue accumulation, and toxic effects of polyurethane microplastics (PUR-MPs) on zebra fish. Materials and Methods: The zebra fish were exposed to different concentrations of PURs-MPs of different sizes for 10 days. Mortality and behavioral changes were monitored. Ingestion and tissue accumulation of PUR-MPs were studied by fluorescent tagging of PUR-MPs. Pathological damages of tissues were investigated with hematoxylin-eosin staining. Results: Microsize PUR-MPs can be ingested by zebra fish and fluorescent-tagged PUR-MPs were found in gills and gastrointestinal (GI) tract of fish after 10 days of exposure. A significant negative correlation was found between fluorescence intensity in fish tissues and size of PUR-MPs. Gills, GI tract, and liver were the most affected tissues by PUR-MP toxicity. GI damages included epithelial detachment, thinning of the bowel wall, congestive inflammation, epithelial damage, and lesions of villi in the gastric wall. Necrosis, adhesion, and partial fusion of secondary lamellae were the dominant pathological damages in the gills. Liver also was affected by cellular necrosis, infiltration, and lipid droplets. Conclusion: Exposure of zebra fish to PUR-MPs leads to ingestion of these particles by fish and significant increase in fish mortality and tissue damages. Particle size and MP concentration were the key determinant factors in PUR-MP toxicity. The results of the present study provide novel insights into environmental toxicity of PUR-MPs and toxic effect of PUR-MPs in aquatic organisms.

Synergistic effects of acute warming and low pH on cellular stress responses of the gilthead seabream Sparus aurata.

The present study assesses the resilience of the Mediterranean gilthead seabream (Sparus aurata) to acute warming and water acidification, using cellular indicators of systemic to molecular responses to various temperatures and CO2 concentrations. Tissue metabolic capacity derived from enzyme measurements, citrate synthase, 3-hydroxyacyl CoA dehydrogenase (HOAD), as well as lactate dehydrogenase. Cellular stress and signaling responses were identified from expression patterns of Hsp70 and Hsp90, the phosphorylation of p38 MAPK, JNKs and ERKs, from protein ubiquitylation and finally from the levels of transcription factor Hif-1α as an indicator of systemic hypoxemia. Exposure to elevated CO2 levels at temperatures higher than 24°C generally caused an increase in fish mortality above the rate caused by warming alone, indicating effects of the two factors and a failure of acclimation and thus the limits of phenotypic plasticity to be reached. As a potential reason, tissue-dependent induction and stabilization of Hif-1α indicate hypoxemic conditions. Their exacerbation by enhanced CO2 levels is linked to the persistent expression of Hsp70 and Hsp90, oxidative stress and activation of MAPK and ubiquitin pathways. Antioxidant defence is enhanced by expression of catalase and glutathione reductase, however, leaving superoxide dismutase suppressed by elevated CO2 levels. On longer timescales in specimens surviving warming and CO2 exposures, various metabolic adjustments initiate a preference to oxidize lipid via HOAD for energy supply. These processes indicate significant acclimation up to a limit and a time-limited capacity to survive extreme conditions passively by exploiting mechanisms of cellular resilience.

The acute and sub-chronic exposures of goldfish to naphthenic acids induce different host defense responses

Naphthenic acids (NAs) are believed to be the major toxic component in oil sands process-affected water (OSPW) produced by the oil sands mining industry in Northern Alberta, Canada. We recently reported that oral exposure to NAs alters mammalian immune responses, but the effect of OSPW or NAs on the immune mechanisms of aquatic organisms has not been fully elucidated. We analyzed the effects of acute and sub-chronic NAs exposures on goldfish immune responses by measuring the expression of three pro-inflammatory cytokine genes, antimicrobial functions of macrophages, and host defense after challenge with a protozoan pathogen (Trypanosoma carassii). One week after NAs exposure, fish exhibited increased expression of pro-inflammatory cytokines (IFNγ, IL-1β1, TNF-α2) in the gills, kidney and spleen. Primary macrophages from fish exposed to NAs for one week, exhibited increased production of nitric oxide and reactive oxygen intermediates. Goldfish exposed for one week to 20mg/L NAs were more resistant to infection by T. carassii. In contrast, sub-chronic exposure of goldfish (12 weeks) to NAs resulted in decreased expression of pro-inflammatory cytokines in the gills, kidney and spleen. The sub-chronic exposure to NAs reduced the ability of goldfish to control the T. carassii infection, exemplified by a drastic increase in fish mortality and increased blood parasite loads. This is the first report analyzing the effects of OSPW contaminants on the immune system of aquatic vertebrates. We believe that the bioassays depicted in this work will be valuable tools for analyzing the efficacy of OSPW remediation techniques and assessment of diverse environmental pollutants.

Advances in fish harvest technologies for circular tanks

Improved equipment and husbandry practices are required to effectively grade and harvest fish in large land-based culture tanks. The objective of our work was to develop and evaluate several types of relatively inexpensive, portable, and efficient fish handling equipment to reduce the labor requirement for grading and harvesting fish from large circular culture tanks. This equipment and husbandry practices also had to provide for worker safety and minimize the stress or damage to the fish. Two techniques were developed and evaluated to remove the entire population from a large and deep circular tank, i.e. (a) purse seine and (b) carbon dioxide avoidance response. Two other techniques were developed and evaluated to remove the fish from a large (150m3) and deep (2.44m) circular culture tank after they had been top-graded in situ using a 3-panel clam-shell grader: (c) an airlift fish pump and hand sorting/dewatering box and (d) a sidewall drain box for hand sorting/dewatering. Some of these technologies are new, while others (such as the purse seine) have been used in other applications. Our commercial-scale evaluation of these technologies provided insight into the advantages and disadvantages of each option. With use of the clam-shell grader, the majority of the fish in the culture tank were never lifted from the water during the self-sorting process, which minimized stress, perhaps enhancing final product quality. In contrast, harvesting the tank using the purse seine and hand brailing was much more labor intensive and increased the stress on the fish, as indicated by a nearly 10-fold increase in fish mortality compared to the mortality observed when the clam-shell type crowder/grader system and an airlift fish pump or sidewall drain box were used during fish harvest. The combination of the clam-shell crowder/grader with the sidewall drain harvest box was our preferred harvest method, because of its low labor requirement, relatively low fish mortality, and rapid harvest rate. We also think that the carbon dioxide avoidance harvest technique can be used effectively, with little labor input and practically zero mortality when the entire fish population must be removed from a fish culture tank, but not during a selective harvest using in situ grading. Ultimately, the more effective technologies and practices should help fish farmers overcome scale-up issues and improve land-based fish farm profitability.

Massive Hepatic Necrosis and Nodular Regeneration in Largemouth Bass Fed Diets High in Available Carbohydrate

AbstractLargemouth bass Micropterus salmoides are piscivorous fish raised on farms then sold live in Asian fish markets on the east and west coasts of the United States. In the winter of 1998, a major producer of feed‐trained bass suffered a significant increase in fish mortality both during shipping and while the fish were still in ponds. No bacterial, viral, or significant parasitic pathogens were found at necropsy. Livers of affected fish were pale and translucent with 3–10 mm pink nodules on their surface and deeper in the parenchyma. Histological examination of these livers showed that the translucent regions of the liver contained few hepatocytes and were composed of tissue consistent with a chronic inflammatory response. Also present were eosinophils, islands of pancreatic and biliary cells, and granulomas that did not stain positively for mycobacteria. The pink nodules were areas of multifocal regeneration of normal hepatocytes. Sequential studies of bass in ponds revealed that the bass were progressively accumulating glycogen in their hepatocytes to an extent sufficient to explain the massive necrosis of that organ. In order to determine the effect of diets varying in available carbohydrate on fish growth, survival, and liver glycogen content, a 12‐wk feeding trial was conducted in aquaria with juvenile largemouth bass. Nitrogen‐free extract values indicated that an extruded trout diet, a steelhead trout diet, and a diet designed to contain 45% protein and 25% fat, contained 35, 27, and 21% carbohydrate, respectively. Weight gain was lowest in fish fed the extruded trout diet, while liver glycogen was significantly higher in fish fed diets with >27% carbohydrate than in fish fed the diet with 21% carbohydrate. The farmer switched to a diet similar to the 45–25 diet used in our trial. Subsequently, 16‐mo‐old fish examined in October 2000 had no hepatic nodules or necrosis, were significantly larger and less variable in size than previous crops, and the farmer experienced no significant losses in ponds or during shipping.

Effects of phosphate on the reproductive symbiosis between bitterling and freshwater mussels: implications for conservation

Summary We examined the effects of phosphorus, an important pollutant in fresh waters, on mussels Anodonta anatina and embryos of European bitterling Rhodeus sericeus amarus. These species are involved in an unusual symbiosis, with the fish depositing eggs inside the mussels' gills, where the embryos develop for 3–6 weeks until the larvae leave the mussel. High concentrations of phosphate (500 μg L−1 and higher) caused a significant increase in the rate of premature expulsion and emergence of bitterling embryos from the mussels, with a concomitant increase in fish mortality. At concentrations of 750 μg L−1 and higher, mussels reduced their frequency of ventilation and movements through the substratum. These results have implications for understanding the nature of the symbiosis between the fish and their mussel hosts, showing that mussels have control over bitterling developing in their gills. The premature expulsion of bitterling embryos at high phosphate levels is detrimental to the fish that they harbour. Recommendations for the conservation of bitterling and species of mussels, which are threatened or endangered over parts of their ranges, include reductions in levels of phosphorus in natural habitats and the need for low levels in reintroduction sites for the fish and their mussel hosts.

The physiological effects of salmon lice infection on post‐smolt of Atlantic salmon

The physiological effects of salmon lice infections on post‐smolt of Atlantic salmon were examined by experimentally infecting hatchery reared post‐smolts with infective copepodids. Even at high infection intensities, ranging from 30–250 lice per fish, early chalimus stages did not have severe, physiological effects on the fish. There was a sudden increase in fish mortality after the appearance of preadult I stages. Infected fish were then suffering due to lesions and osmoregulatory failure. Plasma chloride level increased significantly and total protein, albumin and haematocrit decreased significantly in infected compared to uninfected fish. All infected fish became moribund before adult lice appeared. Infection intensities above 30 salmon lice larvae per fish thus appear to cause death of Atlantic salmon post‐smolt soon after the lice reach their pre‐adult stage.

Theoretical consideration of effect of fishing mortality on growth and reproduction of fish populations

An increase in fish mortality due to fishing can theoretically change the growth and reproduction of fish populations from the viewpoint of adaptation. We address the issue of how an iteroparous fish should convert surplus energy into somatic growth and reproduction at each age under given conditions of mortality. A model of life history, which maximizes the net reproductive rate using the discrete maximum principle, is improved employing a new relationship between body weight and surplus energy which we have recently proposed. The model is applied to the North Sea plaice Pleuronectes platessa, for which it has been reported that the average length of young fish had increased whereas that of old ones had decreased for some decades. Although the model cannot directly explain the former phenomenon, the two phenomena can be interpreted as a change in the optimal life history due mainly to an increase in mortality.