Changes in Hematological, Biochemical and Non-specific Immune Parameters of Olive Flounder, Paralichthys olivaceus, Following Starvation

Fish slaughter practices in Brazilian aquaculture and their consequences for animal welfare

Slaughter is considered an important fish welfare issue. For a slaughter method to be considered humane, effective stunning that lasts until death as well as the reduction of pain and fear throughout all procedures are essential. Our objective was to investigate current techniques for slaughtering fish in Brazil. A digital questionnaire with six multiple-choice and three open questions was distributed to companies registered as fish slaughterhouses and to fish farms in 2019, addressing fish species, quantities processed and slaughter procedures adopted. From 62 facilities in 15 Brazilian states that answered the survey, nine slaughterhouses and 30 fish farms slaughtered fish, totalling 452 tonnes per day. All reported pre-slaughter stunning, and live chilling to be the most commonly cited method (82.0%), followed by electronarcosis (18.0%). Slaughtering techniques included exsanguination (38.5%) and decapitation (2.5%). For the remaining companies, no slaughter method was declared, suggesting death by asphyxiation or by further processing (59.0%). Twenty-nine companies adopted pre-slaughter fasting, lasting from 10 to 48 h. All sites worked with tilapia (100%) and 24 (82.7%) reported that they worked exclusively with this species. Other species reported were: pacu (25.6%), tambacu (17.9%), tambaqui and carp (15.3%), jundiá (12.8%), pintado and pirarucu (7.7%), matrinxã and pangassius (5.1%). Asphyxia and live chilling are not considered humane, as animals remain conscious and, thus, suffer. Results show that most establishments do not perform humane slaughter. This scenario highlights the urgent need for development and enforcement of humane fish slaughter techniques, with routine supervision and normative requirements.

Effect of Bivalent Vaccines against Vibrio anguillarum and Aeromonas salmonicida Subspecie achromogenes on Health and Survival of Turbot

The efficacy of intraperitoneal injection of an oil-based bivalent autogenous vaccine and the commercial vaccine AlphaJect 3000 (Pharmaq AS) to prevent atypical furunculosis and vibriosis in turbot was analyzed. The effect of both vaccines on health parameters and survival of fish after challenge with V. anguillarum and A. salmonicida subsp. achromogenes was tested. The autogenous vaccine conferred high levels of protection and long-lasting immunity against both pathogens with a single dose. However, severe side effects were observed in turbot injected with this autovaccine and minor negative effects with the AlphaJect 3000 vaccine and the adjuvant Montanide or Eolane. All vaccinated fish showed remarkable antibody agglutination titers, higher than those of control fish, which were maintained 160 d after vaccination. In conclusion, the autogenous bivalent vaccine induces long-lasting protection against atypical furunculosis and vibriosis in turbot, after administration of a single dose, at the cost of high side effects in fish. Therefore, the development of new vaccines should focus on autovaccines and the use of liquid paraffin adjuvants that increase protection with reduced or no side effects.

Effects of prolonged fasting on levels of metabolites, oxidative stress, immune-related gene expression, histopathology, and DNA damage in the liver and muscle tissues of rainbow trout (Oncorhynchus mykiss)

This study was conducted to assess the impacts of prolonged fasting (70 and 120 days) on the morphological, biochemical, oxidative stress responses, immune-related gene expression, histopathology, and DNA damage in rainbow trout. Final weight (FW), hepatosomatic index (HSI), and condition factor (CF) significantly decreased in both 70 and 120 days of fasting compared to the pre-fasting group (p < 0.05). Fasting led to a significant reduction in serum blood metabolites (glucose, total protein, triglyceride, T. cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL)) and endogenous reserves (protein and lipid). However, plasma acetylcholinesterase (AChE) activity, aspartate aminotransferase (AST), alanine aminotransferase (ALT), interleukin (IL1), tumor necrosis factor (TNF1α), and transferrin (TF) increased significantly (p < 0.05). While malondialdehyde (MDA) levels compared to the pre-fasting group increased in the liver and muscle tissues (70 and 120 days), glutathione (GSH) enzyme activities decreased significantly in both tissues (p < 0.05). Histopathologically, both fasting groups (70 and 120 days) when compared to the pre-fasting group led to steatosis, necrosis and degeneration in hepatocytes, inflammation and hyperemia in the liver tissue and hyaline degeneration, atrophy, and inflammation in muscle tissue. Additionally, 8-OHdG levels of the liver and muscle tissues at 120 days' fasting were more severe according to 70 days' fasting. Finally, blood, the liver, and muscle tissues may be helpful to assess the impacts of fasting and fasting stress in rainbow trout.

Acute response of refeeding in tambaqui submitted to long-term fasting

ABSTRACT This study aimed evaluate energetic mobilization in tambaqui submitted to fasting, after a one-day refeeding. 120 tambaqui juveniles were distributed in 12 310L polyethylene boxes. Three treatments were evaluated: Control (14 days of feeding); Fasting for 14 days; and Refeeding (13 days fasting and one day of feedback). After the experimental period, the fish were anesthetized with eugenol for blood collection and serum and plasma were used to measure glucose, triglycerides, cholesterol and serum protein. Subsequently, fish were euthanized to remove liver and mesenteric fat and were used to determine hepatic glycogen and lipid and mesenteric fat index. The results were submitted to ANOVA and the means compared by Tukey test when statistical significance was observed (P <0.05). Glucose, triglycerides and serum protein decreased after fasting, differing statistically with the control. Refeeding resulted in the recovery of three blood indicators. Liver analysis shows glycogen was consumed intensely during fasting and partially recovered after refeeding, when compared to control group. The results obtained in this study suggest that the 14-day fast was not harmful to the fish and the tambaqui are able to quickly adjust their metabolism according to their nutritional status.

The role of glucocorticoids in the vertebrate response to weather

Changes in the environment related to inclement weather can threaten survival and reproductive success both through direct adverse exposure and indirectly by decreasing food availability. Glucocorticoids, released during activation of the hypothalamic-pituitary-adrenal axis as part of the stress response, are an important candidate for linking vertebrate coping mechanisms to weather. This review attempts to determine if there is a consensus response of glucocorticoids to exposure to weather-related stimuli, including food availability, precipitation, temperature and barometric pressure. The included studies cover field and laboratory studies for all vertebrate taxa, and are separated into four exposure periods, e.g., hours, days, weeks and months. Each reported result was assigned a score based on the glucocorticoid response, e.g., increased, no change, or decreased. Short-term exposure to weather-related stimuli, of up to 24 h, is generally associated with increased glucocorticoids (79% of studies), suggesting that these stimuli are perceived as stressors by most animals. In contrast, the pattern for exposures longer than 24 h shows more variation, even though a majority of studies still report an increase (64%). Lack of glucocorticoid increases appeared to result from instances where: (1) prolonged exposure was a predictable part of the life history of an animal; (2) environmental context was important for the ultimate effect of a stimulus (e.g., precipitation limited food availability in one environment, but increased food in another); (3) prolonged exposure induced chronic stress; and (4) long-term responses appeared to reflect adaptations to seasonal shifts, instead of to short-term weather. However, there is a strong bias towards studies in domesticated laboratory species and wild animals held in captivity, indicating a need for field studies, especially in reptiles and amphibians. In conclusion, the accumulated literature supports the hypothesis that glucocorticoids can serve as the physiological mechanism promoting fitness during inclement weather.

Effects of food availability on growth performance and immune-related gene expression of juvenile olive flounder (Paralichthys olivaceus)

Unfavorable environmental conditions and inappropriate culture practices have increased the vulnerability of cultured fish to disease infection. Up to date many studies have aimed to determine a feeding regimen to maximize productivity; however, very little information on immune responses of cultured fish in response to underfeeding or overfeeding is available. Therefore, a preliminary study was conducted to evaluate effects of graded feeding levels (i.e., food availability) on growth performance and immune-related gene expression of juvenile olive flounder (Paralichthys olivaceus). Six different feeding rates including 1, 4, 7, 10, 13, and 16% body weight per day (BW/d) were randomly assigned to three replicate tanks stocking 150 fish (average initial body weight: 0.27 ± 0.02 g; mean ± SD) per tank. A feeding trial lasted for two weeks. Based on the results of the weight gain, nutrient gain, and whole-body compositions and energy content, the feeding rate of 10%, 13%, and 16% BW/d resulted in high nutritional status, whereas the feeding rate of 1% and 4% BW/d resulted in low nutritional status. Intermediate nutritional status was observed at the feeding rate of 7% BW/d. In the given rearing conditions the optimum feeding rate resulting in the maximum growth was estimated to be 11.9% BW/d based on the quadratic broken-line regression model, chosen as the best-fit model among the tested models. Expression of immune-related genes including IL-8 and IgM was significantly down-regulated in the flounder fed at 1% BW/d in comparison to those fed at 7% BW/d. Interestingly, expression of these genes in the flounder fed at 10%, 13%, and 16% BW/d was relatively down-regulated in comparison to that of the flounder fed at 7% BW/d. Although no statistical difference was detected, overall response patterns of other immune-related genes, including TLR3, polymeric Ig receptor, lysozyme C-type, GPx, SOD, and Trx followed what IL-8 and IgM exhibited in response to the various feeding rates. Given the current challenges in aquaculture of the flounder our findings suggest to prohibit underfeeding or overfeeding (i.e., ad-libitum feeding) when culturing the young flounder.

Protein and lipid metabolism adjustments in silver catfish (Rhamdia quelen) during different periods of fasting and refeeding

The fish may experience periods of food deprivation or starvation which produce metabolic changes. In this study, adult Rhamdia quelen males were subjected to fasting periods of 1, 7, 14, and 21 days and of refeeding 2, 4, 6, and 12 days. The results demonstrated that liver protein was depleted after 1 day of fasting, but recovered after 6 days of refeeding. After 14 days of fasting, mobilization in the lipids of the muscular tissue took place, and these reserves began to re-establish themselves after 4 days of refeeding. Plasmatic triglycerides increased after 1 day of fasting, and decreased following 2 days of refeeding. The glycerol in the plasma oscillated constantly during the different periods of fasting and refeeding. Changes in the metabolism of both protein and lipids during these periods can be considered as survival strategies used by R. quelen. The difference in the metabolic profile of the tissues, the influence of the period of fasting, and the type of reserves mobilized were all in evidence.

Energy deficit does not affect immune responses of experimentally infected pacu (Piaractus mesopotamicus)

We investigated if the energy deficit following a 30-day starvation period could affect the ability of fish to mount immune responses after experimental exposure to Aeromonas hydrophila. Fish were submitted to two feeding strategies during 30 days: starvation and continuously feeding. Fish were then sampled to allow for the assessment of baseline metabolic and immune system indicators, were next intraperitonially inoculated with A. hydrophila, and finally were sampled at 3 and 24 h after the challenge. The respiratory activity of leukocytes was lower in starved fish at baseline, increasing after bacterial inoculation to levels similar to those seen among fed fish. Levels of serum lysozyme were higher in starved fish at baseline. The same response profile was observed 3 h after inoculation, but among fed fish, these levels increased to values similar to those of starved fish 24 h after infection. Among starved fish, lysozyme concentration did not change over the course of the experiment. The serum ACH activity was lower in starved fish at baseline and increased after bacterial inoculation in both fish groups. Baseline levels of blood glucose of starved fish were lower than those of fed fish and increased 3 h after bacterial inoculation in both fish groups, decreasing in both groups at 24 h after inoculation. Baseline liver glycogen levels were similar in both fish groups and higher than at 3 and 24 h after inoculation. Three hours after bacterial inoculation, liver glycogen was less reduced in fed fish. Baseline levels of blood triglycerides were lower in starved fish and the profile remained unchanged 3 h after inoculation. There was a gradual decrease in fed fish, and the levels of starved fish remained unchanged throughout the observation period. Blood glycerol levels at baseline were higher in starved fish than in fed fish and remained unaltered at 3 h after inoculation. However those levels increased at 24 h. In fed fish there was a gradual increase of glycerol levels up to 24 h after bacterial inoculation. Baseline liver lipid levels of starved fish were lower and this difference in the response profile remained unchanged 3 and 24 h after inoculation. The liver lipid levels of starved fish decreased after inoculation, and remained unchanged in fed fish. As observed in liver lipid, muscle lipid levels of starved fish were lower than in fed fish, throughout the experiment. Starved fish levels remained unchanged; however fed fish levels decreased 24 h after bacterial inoculation. Levels of cortisol were higher in starved fish at baseline and increased in both fish groups 3 h after bacterial inoculation, reaching intermediary levels 24 h after inoculation. Our results show that in pacu, although mounting an immune response triggered after bacterial exposure is an energy-expensive process, fish under energetic deficit status were able to display protection against infection.