Effects of temperature, salinity, body length, and starvation on the critical swimming speed of whiteleg shrimp, Litopenaeus vannamei

Effect of dissolved metabolites of the dinoflagellate Gymnodinium catenatum (Graham, 1943) on the white shrimp Litopenaeus vannamei (Boone, 1931): A histological study

Harmful algae blooms (HABs) are a conspicuous phenomenon that affect the coastal zone worldwide. Aquaculture industry zones are not excluded from being affected by HAB that cause organism mortality and jeopardize their innocuity due to the contamination by phytotoxins with the concomitant economic losses. Direct ingestion of metabolites from HAB species or organisms contaminated with phycotoxins together with dermal absorption of dissolved metabolites (DM), including toxins, are the two main routes of poisoning. From these poisoning routes, the effect of DM, particularly paralytic shellfish toxins (PST), has been relatively understudied. This intoxication route can be conspicuous and could be involved in many significant mortalities of cultivated marine organisms. In this study, white shrimp juveniles (2.1 g wet weight) of Litopenaeus vannamei were exposed to extracts of 10⁴, 10⁵ and 10⁶ cells/L of the dinoflagellate Gymnodinium catenatum, a PST producer. The experiment ended after 17 h of exposure when shrimps exposed to 10⁶ cells/L extract started to die and the rest of the shrimps, from this and other treatments, did not respond to gentle physical stimulus and their swimming activity was low and erratic. Toxin concentrations were determined using high performance liquid chromatography while qualitative and quantitative histological damages were assessed on the tissues. In general, most toxins were accumulated in the hepatopancreas where more than 90% were found. Other tissues such as intestine, muscle, and gills contained less than 10% of toxins. Compared to the control, the main significative tissue damages were, loss of up to 80% of the nerve cord, 40% of the muscle coverage area, and reduction of the gill lamella width. Also, atrophy in hepatopancreas was observed, manifested by a decrease in the height of B cells, lumen degeneration and thinning of tubules. Some damages were more evident when shrimps were exposed to higher concentrated extracts of G. catenatum, however, not all damages were progressive and proportional to the extract concentration. These data confirm that PST dissolved enter the shrimp, possibly via the gills, and suggest that dissolved metabolites, including PST, may cause tissue damage. Other dissolved metabolites produced by G. catenatum, alone or in synergy, may also be involved. These results also pointed out the importance of dissolved molecules produced for this dinoflagellate and the potential effect on cultured shrimp.

Cellular stress response and acclimation capacity of the ditch shrimp Palaemon varians to extreme weather events - How plastic can a plastic species be?

Species from shallow marine environments are particularly vulnerable to extreme weather events (heatwaves and extreme rainfall) that can promote abrupt environmental shifts, namely in temperature and salinity (respectively). To assess how these shifts impact species' cellular stress responses (CSR), ditch shrimps Palaemon varians were exposed to a chronic (28 days) thermohaline stress experiment. Three levels of temperature (20, 23 and 26 °C) and two levels of salinity (20 and 40) were tested in a full factorial experiment, and shrimps sampled at the 7th, 14th, 21st and 28th day of exposure. Survival, wet weight (as proxy for growth), and cellular stress biomarkers associated with oxidative stress (LPO - Lipid Peroxidation, GST - Glutathione-S-Transferase, SOD - Superoxide Dismutase, TAC - Total Antioxidant Capacity and CAT - Catalase) and protein denaturation (UBI - Ubiquitin and HSP-70 - Heat Shock Protein 70 kDa) were analysed in shrimps' muscle at each sampling day. Temperature and time of exposure significantly affected biomarker levels, with shrimps exposed to 20 and 26 °C revealing more pronounced differences. No interactions were detected between temperature and salinity, suggesting that these factors display additive effects on shrimps' CSR. Antioxidant agents (CAT and TAC) increased under elevated temperature, while protein denaturation markers (UBI and HSP-70) were mostly affected by time of exposure, decreasing at 28 days. Total protein reserves increased throughout time and no effects on wet weight were observed. A negative correlation between wet weight and HSP-70 was detected, suggesting that HSP-70 levels are dependent on organism size. Peak survival (~73 %) was found under 20 °C and salinity 40 and lower survival (~30-40 %) was associated with higher temperatures (23 and 26 °C) and lower salinity (20). We conclude that P. varians displays some level of acclimation capacity but differences in survival may indicate effects on osmoregulation processes and the need for longer timeframes to fully acclimate to heat and hyposaline stress.

Physiological basis of interactive responses to temperature and salinity in coastal marine invertebrate: Implications for responses to warming

Developing physiological mechanistic models to predict species' responses to climate-driven environmental variables remains a key endeavor in ecology. Such approaches are challenging, because they require linking physiological processes with fitness and contraction or expansion in species' distributions. We explore those links for coastal marine species, occurring in regions of freshwater influence (ROFIs) and exposed to changes in temperature and salinity. First, we evaluated the effect of temperature on hemolymph osmolality and on the expression of genes relevant for osmoregulation in larvae of the shore crab Carcinus maenas. We then discuss and develop a hypothetical model linking osmoregulation, fitness, and species expansion/contraction toward or away from ROFIs. In C. maenas, high temperature led to a threefold increase in the capacity to osmoregulate in the first and last larval stages (i.e., those more likely to experience low salinities). This result matched the known pattern of survival for larval stages where the negative effect of low salinity on survival is mitigated at high temperatures (abbreviated as TMLS). Because gene expression levels did not change at low salinity nor at high temperatures, we hypothesize that the increase in osmoregulatory capacity (OC) at high temperature should involve post-translational processes. Further analysis of data suggested that TMLS occurs in C. maenas larvae due to the combination of increased osmoregulation (a physiological mechanism) and a reduced developmental period (a phenological mechanisms) when exposed to high temperatures. Based on information from the literature, we propose a model for C. maenas and other coastal species showing the contribution of osmoregulation and phenological mechanisms toward changes in range distribution under coastal warming. In species where the OC increases with temperature (e.g., C. maenas larvae), osmoregulation should contribute toward expansion if temperature increases; by contrast in those species where osmoregulation is weaker at high temperature, the contribution should be toward range contraction.

Palatability Enhancement Potential of Hermetia illucens Larvae Protein Hydrolysate in Litopenaeus vannamei Diets

Marine feed ingredients derived from cephalopods (e.g., squid) and crustaceans (e.g., krill) are commercially used to improve the palatability of shrimp diets. Increase in global demand for shrimps has resulted in overfishing of these marine organisms and is a matter of concern. Insect protein hydrolysate could be a sustainable alternative for the possible replacement of these marine feed ingredients. During this study, four formulations: diet A (control: not containing any palatability enhancer), diet B (containing squid meal and krill oil), diet C (containing 1% insect protein hydrolysate), and diet D (containing 2% insect protein hydrolysate) were tested for (1) time required by first subject to begin feeding (time to strike) and (2) palatability in Litopenaeus vannamei. Additionally, the chemical composition of all four diet formulations was also analyzed. Results indicate that all diets had similar crude composition. The major essential amino acids in all diets were leucine and lysine, whereas eicosapentaenoic acid was the major omega-3 fatty acid in all diets. There were no significant differences between the mean time to strike for all the tested formulations. Palatability of tested formulations was found in the following order: diet D > diet C > diet B = diet A (p < 0.05), indicating that addition of squid meal and krill oil has no effect on palatability in comparison to control, whereas inclusion of insect protein hydrolysates significantly improves the palatability of formulations. Palatability enhancement potential of insect protein hydrolysate could be attributed to the high free amino acid content and water solubility in comparison to squid meal.

Simultaneous eco-toxicity assessment technique using an online monitoring system: effects of different environmental factors on swimming behavior of zebrafish (Danio rerio)

Environmental factors, such as photoperiod and temperature were the main limiting factors for the survival of organisms in the nature environment. Changes in environmental factors are well predicted but determining their effects on organisms are challenging hot topic in the field of eco-toxicology. Thus, technology based eco-toxicity assessment was focused worldwide. In this research, the effects of different temperatures (15 °C, 22 °C, 30 °C, 32 °C, and 35 °C) and photoperiods (dark and light periods) on the continuous behavior responses of Zebrafish (Danio rerio) were investigated using an online monitoring system (OMS). We designed a new fish chamber with sensors to measure the behavior responses of zebrafish under different conditions. Data obtained from the OMS could be assessed for factors such as difference in swimming behavior, circadian rhythm, and avoidance behavior using latest software (MATLAB). The observed behavior anomalies on zebrafish under different temperatures and continuous photoperiods were statically significant (p < 0.05). We conclude that the new designed fish chamber (behavior sensors) is good in sensing behavioral responses of zebrafish under different conditions. The fish behavior strength could be a potential biomarker to assess the effects of environmental factors. The present study would be a basic platform for assessing the effects of different stressors simultaneously on swimming behavior of zebrafish.

Gait-specific adaptation of locomotor activity in response to dietary restriction in Caenorhabditis elegans

Locomotion is crucial for the survival of living organisms, as it allows foraging, flight and mating behaviour. In response to environmental cues, many organisms switch between alternative forms of locomotion, referred to as gaits. The nematode Caenorhabditis elegans exhibits two gaits: swimming in liquids and crawling on dense gels. The kinematics and patterns of muscle activity differ between the two gaits, with swimming being less efficient than crawling. We found that C. elegans when grown on dietary restriction (DR) plates and then tested immediately for swimming activity exhibit an accelerated frequency of body-bending swimming compared with ad libitum-fed worms, resulting in an increased swimming speed. This response is independent of the presence or absence of food bacteria in the assay liquid. In contrast, the crawling speed of DR worms on assay agar plates is decreased and influenced by food availability. Because DR also attenuates the disturbed swimming activity of worms that are deficient in the presynaptic dopamine transporter DAT-1, our data link DR-induced alterations of the swimming gait to synaptic processes. This strongly suggests a biochemical rather than a biomechanical response to DR provoked by changes in the worm's body structure. We conclude that the increase in locomotor activity in response to DR is specific to the swimming gait and might represent a survival strategy, allowing food-deprived nematodes to exit unfavourable environments.