Effects of long-term feed deprivation on body weight loss, muscle composition, plasma metabolites, and intermediate metabolism of meagre (Argyrosomus regius) under different water temperatures

Effects of starvation on the pharmacokinetics and optimal dosages of florfenicol and associated serum biochemistry in Asian seabass (Lates calcarifer)

Starvation has influence on physiology and pharmacokinetic (PK) characteristics of many drugs in land animals. However, similar PK information in fish is lacking. The current study examined the effects of starvation on fish PK, taking florfenicol (FF) in Asian seabass as an example. FF was orally administered at a single dose of 10 mg/kg into 35-day starved fish reared at 25 and 30°C and the serum FF concentration was analyzed by HPLC-FLD. At 30°C, the absorption and elimination half-lives of the starved fish were increased by 30% (from 0.44 to 0.57 h) and 55% (from 7.2 to 11.18 h), respectively. The volume of distribution, clearance, and area under the curve were changed from 1.25 to 0.71 L/kg, 0.120 to 0.044 L/kg/h, and 88 to 228 h·μg/ml, respectively. Similar starvation-induced PK changes were also observed at 25°C. The serum biochemical parameters, mainly the alanine aminotransferase, aspartate aminotransferase, and glucose levels, were significantly reduced in the starvation group. Overall, FF absorption, distribution, and elimination rates were reduced by starvation, resulting in four to five times lower optimal dosage than the non-starved fish. Drug treatment in starved fish should be treated with caution as overdosing and/or tissue residues could perceivably occur.

Temperature-dependent metabolic consequences of food deprivation in the European sardine

Aquatic ecosystems can exhibit seasonal variation in resource availability and animals have evolved to cope with the associated caloric restriction. During winter in the NW Mediterranean Sea, the European sardine Sardina pilchardus naturally experiences caloric restriction owing to a decrease in the diversity and quantity of plankton. However, ongoing global warming has had deleterious effects on plankton communities such that food shortages may occur throughout the year, especially under warm conditions in the summer. We investigated the interactive effects of temperature and food availability on sardine metabolism by continuously monitoring whole-animal respiration of groups of control (fed) and food-deprived sardines over a 60-day experiment in winter (12°C) or summer (20°C) conditions under natural photoperiod. In addition, we measured mitochondrial respiration of red muscle fibres, biometric variables and energy reserves of individuals sampled at 30 and 60 days. This revealed that winter food deprivation elicits energy saving mechanisms at whole animal and cellular levels by maintaining a low metabolism to preserve energy reserves, allowing high levels of survival. By contrast, despite energy saving mechanisms at the mitochondrial level, whole animal metabolic rate was high during food deprivation in summer, causing increased consumption of energy reserves at the muscular level and high mortality after 60 days. Furthermore, a 5-day re-feeding did not improve survival, and mortalities continued, suggesting that long-term food deprivation at high temperatures causes profound stress in sardines that potentially impairs nutrient absorption.

Metabolic scope, performance and tolerance of juvenile European sea bass Dicentrarchus labrax upon acclimation to high temperatures

European sea bass is a species of great commercial value for fisheries and aquaculture. Rising temperatures may jeopardize the performance and survival of the species across its distribution and farming range, making the investigation of its thermal responses highly relevant. In this article, the metabolic scope, performance, and tolerance of juvenile E. sea bass reared under three high water temperatures (24, 28, 33°C), for a period of three months was evaluated via analysis of selected growth performance and physiological indicators. Effects on molecular, hormonal, and biochemical variables were analyzed along with effects of acclimation temperature on the metabolic rate and Critical Thermal maximum (CT_max). Despite signs of thermal stress at 28°C indicated by high plasma cortisol and lactate levels as well as the upregulation of genes coding for Heat Shock Proteins (HSP), E. sea bass can maintain high performance at that temperature which is encouraging for the species culture in the context of a warming ocean. Critical survivability thresholds appear sharply close to 33°C, where the aerobic capacity declines and the overall performance diminishes. European sea bass demonstrates appreciable capacity to cope with acute thermal stress exhibiting CT_max as high as 40°C for fish acclimated at high temperatures, which may indicate resilience to future heatwaves events.

Thermal tolerance, metabolic scope and performance of meagre, Argyrosomus regius, reared under high water temperatures

This article reports on the thermal tolerance, metabolic capacity and performance of juvenile meagre (Argyrosomus regius) reared under three high water temperatures (24, 29 and 34 °C) for three months. The analysis includes the thermal effects on the growth performance, metabolism and physiology of meagre, including a range of molecular, haematological, metabolic, enzymatic and hormonal indicators, as well as the effects on the proximate composition and ingestion speed. Meagre performs best between 24 and 29 °C while the temperature of 34 °C is very close to the upper end of its temperature tolerance range. At 34 °C meagre exhibits a poor growth performance and physiological status, increased blood clotting, high mortality rates and a diminished capacity for aerobic metabolism, as indicated by its low aerobic scope (129 mg kg^-1 h^-1). Meagre may tolerate short exposures to high temperatures after sufficient acclimation (Critical thermal maximum of 37.5 °C after acclimation to 29 °C) but its overall performance declines under prolonged exposure, suggesting that this emerging aquaculture species may be vulnerable to global warming. Our work corroborates previous findings on the thermal preferences of the species, identifies critical biological thresholds, and provides insights into the effects of prolonged exposure to high temperature regimes.

Response of juvenile Lophiosilurus alexandri to osmotic and thermic shock

The objective of the present study was to evaluate the physiological responses of juvenile Lophiosilurus alexandri submitted to osmotic and thermic shock. Thirty juveniles were used for each test, of which 10 were not subjected to stress and remained in normal conditions (fresh water at 28.0 °C). The others were submitted to stress shock (saline water of 10.0 g of salt/L or water cooled to 18.0 °C). Blood samples were taken at 0 h (no exposure to the stress factor) and 1 h and 24 h after the tests. At 24 h, the survivorship was 100% in both tests. In both the osmotic and thermic shock tests, cortisol and glucose levels were higher at 1 h but then decreased after 24 h. Lactate dehydrogenase showed differences in the temperature test, but there was no difference between 1 and 24 h after exposure to osmotic shock (P > 0.05). The difference was recorded in blood gas variables (pH, PvCO₂, PvO₂, hemoglobin, sO₂, BE, tCO₂, HCO₃^-, and stHCO₃^-) and electrolytes (Na⁺, Ca⁺⁺, nCa⁺⁺, and K⁺) in both experiments. With regard to hematology and blood biochemistry, exposure to thermal shock did not affect (P > 0.05) ALP, total plasma protein, hematocrit, and ALT and AST at 1 h and 24 h. ALP and total protein in the blood of fish submitted to the osmotic shock were lowest (P < 0.05) at 24 h. Leukocyte and erythrocyte counts exhibited differences after osmotic shock, in contrast to erythrocyte counts of the temperature test, which did not change in 24 h (P > 0.05). Juveniles of L. alexandri were able to reestablish the main indicators of stress (cortisol, glucose), while the others (hematological, biochemical, and gasometric) varied in compensation for normal physiological reestablishment.

Effect of starvation and refeeding on growth, gut microbiota and non-specific immunity in hybrid grouper (Epinephelus fuscoguttatus♀×E. lanceolatus♂)

Environmental changes can lead to food deprivation among aquatic animals. The main objective of this present research was to assess the effect of starvation and refeeding on growth, gut microbiota and non-specific immunity in a hybrid grouper (Epinephelus fuscoguttatus♀×E. lanceolatus♂). A total of 120 fish with an average weight of 74.16 ± 12.08 g were randomly divided into two groups (control group and fasted-refed group). The control group was fed until satiation for 60 days, while the fasted-refed group was fasted for 30 days and then fed to satiation for 30 days. The results showed that starvation led to a significantly decreased growth performance parameters [weight gain rate (WGR) and specific weight gain rate (SGR), while the feeding rate (FR) ] increased during the refeeding, non-specific immunity was significantly improved (p < 0.05) during the first 15 days of starvation, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), lysozyme (LYM) and catalase (CAT). However, non-specific immunity decreased at 30 days of starvation, the expression of genes related to immunity, such as TNF-α, was upregulated (p < 0.05) during starvation, while the expression levels of IL-17 and IFN-γ was reduced (p < 0.05). The expression of IFN-γ and IL-1β peaked during refeeding. Starvation led to significantly decreased abundance and diversity of intestinal microflora, with a higher abundance of Vibrio and a lower abundance of Brevibacillus, Bifidobacterium, Alloprevotella in the fasted-refed group during refeeding than in the control group. The above results reveal that starvation stimulates changes in growth, non-specific immunity, and the gut microbiota, providing new insights for the study of fish habitat selection and adaptability to environmental changes.

Duration of stunting impacts compensatory growth and carcass quality of farmed milkfish, Chanos chanos (Forsskal, 1775) under field conditions

An 18-months field trial was performed to explore the effect of duration of stunting on growth, digestive enzymes and carcass quality in Chanos chanos. Milkfish fry (weight of 1.25 ± 0.03 g and length of 5.53 ± 0.03 cm) were stocked in earthen ponds of 0.02 ha, in triplicate, for different duration of stunting, viz., 4 months (Treatment-1; T4), 8 months (Treatment-2; T8) and 12 months (Treatment-3; T12) and a normal seed (Control; C) separately. In the stunting phase, fish were stocked at higher stocking density (0.2 million/ha) and fed de-oiled rice bran at sub-optimal level. Post-stunting or re-feeding phase commenced immediately after completion of respective stunting duration and fish were reared for the rest of the period to complete the total rearing period of 18 months. In post-stunting, fish stocking density was adjusted to (5000 pieces/ha) and fed at an optimum level (3%). At the end of stunting phase, the study found a significant reduction in growth, survival, digestive enzymes activity, except protease in the T4 group, and carcass nutrients composition of stunted fish. However, in the initial phase of post-stunting, T8 group exhibited an elevated specific growth rate (5.00 ± 0.092%/day), body weight gain (80.82 ± 1.28 g), amylase (0.585 ± 0.021 U/mg protein), protease (5.48 ± 0.13 U/mg protein), and lipase activity (7.92 ± 0.32 U/mg protein). All stunted fish groups displayed a compensatory growth response in post-stunting, but a complete growth compensation was observed in T8 group, which resulted in better feed conversion ratio (3.03 ± 0.04) feed efficiency ratio (0.33 ± 0.01), protein efficiency ratio (1.91 ± 0.03), survival (91.38 ± 0.07%) and digestive enzyme activities. Similarly, at the end of post-stunting, carcass analysis revealed a complete restoration of nutrients in stunted fish and significantly higher protein content in T8 group. Further, the study found lower meat and higher bone contents in normally reared fish than the post-stunted fish which revealed the carcass quality improvement in post-stunted fish thus indicates superiority of the stunting process over normal rearing. Overall, the study suggests that stunting of milkfish, for 8 months (T8), positively affects its growth, survival, digestive enzyme activities and carcass quality which in turn, shall help to overcome the contemporary challenges in milkfish culture.