Climate Change, Disease Prevelance and Physiology of.pptx

Climate Change, Disease Prevelance and Physiology of Fishes.

1. Climate Change, Disease Prevalence and Physiology of Fish Rajarshi bandyopadhyay

2. INTRODUCTION There is increasing concern over the consequences of climate change for fisheries production and the state of marine ecosystems. Climate change is an additional pressure on top of the many (fishing mortality, loss of habitat, pollution, disturbance, introduced species) which fish stocks already experience

3. T he implications of climate change for fish populations can be seen to result from phenomena at four interlinked levels of biological organization:

4. Effect of temperature Fish growth Fish generally show temperature optima for growth and survival (Brett 1959; Gadomski & Caddell 1961). These may change with age and size, as juveniles of many species prefer warmer temperatures than adults do. Early life stages may also have different optimal temperatures, which may reflect temporal and spatial field distributions. These differences appear not only between species but also within species , for example, related to differences in thermal windows due to acclimation or permanent population differences. Most fish are in thermal equilibrium with the surrounding water due to efficient counter current heat exchange between the water and blood at the gills (Stevens & Sutterlin ).

5. The thermal tolerances of fish have been described by Fry (1971) as consisting of lethal, controlling, and directive responses, which indicate that fish will respond to temperature long before it reaches their lethal limits. Moderate temperature increases may increase growth rates and food conversion efficiency, up to the tolerance limits of each species. Thermal tolerance of marine organisms is non-linear , with optimum conditions at midrange and poorer growth at temperatures which are too high or too low.

6. Pörtner (2002) describes an interaction of thermal preference and oxygen supply, such that the capacity to deliver oxygen to the cells is just sufficient to meet the maximum oxygen demand of the animal between the high and low environmental temperatures to be expected. According to Pörtner and Knust (2007), it is the lack of oxygen supply to tissues as conditions warm and metabolic demands increase that lead to altered distributions or extinction of fish from cooler conditions. Larger individual s may be at greater risk of this effect as they may reach their thermal aerobic limits sooner than smaller individuals ( Pörtner and Knust , 2007). CONCEPT OF OCLTT

7. In the pejus range, which is between the optimum and pessimum ranges, animals can still survive, but with a reduced scope for aerobic activity.

8. In a study of the effects of temperature changes on rainbow trout (Oncorhynchus mykiss) in the presence of low pH and high nitrogen, Morgan, McDonald and Wood (2001) found improved growth during winter with a 2 °C temperature increase but decreased growth in summer when the 2 °C increase was added to the already high temperatures. Therefore, seasonal influences and instances when such changes occur may be equally (or more) important than changes expressed on an annual basis. The term “ bioclimate envelope ” has been used to define the interacting effects and limits of temperature, salinity, oxygen, etc. on the performance and survival of species (e.g. Pearson and Dawson, 2003).

9. BIOCLIMATIC ENVELOPE MODEL FOR CLIMATE CHANGE

10. The consequences of the stress response ultimately depend on whether the stressor initiating the response is acute (temporary) or chronic (long-term). Acute stressors may have positive effects on fish physiological function (e.g., stress-hardening; Schreck 2010), but chronic stressors are energetically costly to fishes and divert energy supplies away from growth and reproduction, and may ultimately result in mortality. For example, Gregory and Wood (1999) found that chronically elevated plasma cortisol concentrations decreased growth, appetite, and condition of Rainbow Trout. Similarly, Peterson and Small (2005) found elevated cortisol decreased growth in Channel Catfish Ictalurus punctatus decreased growth.

11. Ectothermic fish metabolic and oxygen uptake rates are profoundly influenced by temperature (Fry 1947), which is reflected by the exponential increase in SMR ( Standard Metabolic Rate) with increasing temperature, and the rapid increase, plateau, and eventual decline of MMR with warming temperatures. Each individual, population, and species thus has a temperature where aerobic scope is optimal ( T opt ; Jonsson and Jonsson 2009), a range of temperatures where specific aerobic activities (e.g., migration, digestion) are possible (i.e., the functional thermal tolerance window), and critical threshold temperatures where aerobic scope is zero and mortality is imminent.

12. Temperature affects their metabolic rate and thus their energy balance and behavior, including locomotor and feeding behavior. Temperature influences the ability/desire of the fish to obtain food , and how they process food through digestion, absorb nutrients within the gastrointestinal tract, and store excess energy. As fish display a large variability in habitats, feeding habits, and anatomical and physiological features , the effects of temperature are complex and species-specific.

13. Thermal windows are narrow in early life stages, due to developmental constraints and insufficient capacity of central organs in the larvae ( Portner et al. 1988) and widen in juveniles and young adults in line with rising performance capacity at small body size. Larger individuals then become more thermally sensitive, due to progressively falling oxygen supply capacity in relation to demand ( Portner & Farrell 1991). Low temperatures during winter may increase mortality, either because temperatures fall outside the thermal window or because energy reserves become limiting , especially in smaller individuals that have relatively fewer reserves compared to larger conspecifics.

14. An increase in juvenile growth as well as an increase in temperature may result in a decrease in the length and age at first maturation, affecting the growth of adults as surplus energy is channeled into reproduction at an earlier age and smaller size. Growth rate, food intake and feed efficiency ratio of juvenile Atlantic salmon smolts were significantly influenced by temperature and fish size. Increased growth at elevated temperatures agrees with previous studies on Atlantic salmon (Solbakken et al). In brown trout reared in freshwater, a decrease in appetite has been observed when temperature exceeds 18 C . Port et al .reported a linear relationship between specific growth rate (SGR) and temperature in Atlantic salmon smolts in seawater between 4.6 and 14.4 C, while a rapid decrease in growth rate was observed when temperature reached 18.9 C.

15. Wurtsbaugh & Davis (1987) found no temperature effect on growth efficiency when fish were being fed high ration levels. But in many species, digestion is associated with selection of a higher body temperature (Peterson et al.; Dorcas et al.) and it is possible that the postprandial thermophilic response enables a more efficient and/or faster digestion. Specific dynamic action, also known as thermic effect of food or dietary induced thermogenesis , is the amount of energy expenditure above the basal metabolic rate due to the cost of processing food for use and storage.

16. IMPACT OF SALINITY In the salmonid Oncorhynchus keta (chum salmon), increasing the salinity to 33.5 psu during rearing, following 7 weeks in FW (7–10 g fish), resulted in increased growth (Kojima et al.). This was demonstrated for smoltifying salmonids, where the smolt status profoundly influenced salinity ‘receptivity ’, osmotic capacities and growth (Boeuf). The metabolic rate of newly hatched steelhead trout (O. mykiss) alevins was significantly lower in 8 psu water, and higher at 12, in comparison to either 0 or 4 psu

17. Climate Change and Fish Physiology The capacity of fishes to cope with environmental variation is considered to be a main determinant of their fitness and is partly determined by their stress physiology. By 2100 , global ocean temperature is expected to rise by 1–4°C , with potential consequences for stress physiology. As ectotherms, fishes are expected to be particularly vulnerable to global warming. Rapid temperature increases are known to induce acute stress responses in fishes and might be of ecological relevance in particular situations.

18. Temperature is known to affect the enzyme reaction, immune response, haematological parameters and plasma electrolytes ( Tanck et al.). In recent years haematological indices have been used to determine the effect of stress ( Wedemeyer & Yasutake ). In fish, cold temperatures increase the oxygen requirement, cardiac output and blood flow (Julian et al.) and in common carp (Cyprinus carpio ) haemolysis has been reported during acute water temperature changes from 8 to 4 ° C (Chen et al.).

19. An increase in the WBC count was found in rainbow trout ( Oncorhynchus mykiss ) (Houston et al.) and carp ( Engelsma et al.) at high temperature and after cold shock, respectively. Ndong et al. found that WBC counts decreased significantly when Mozambique tilapias (O. mossambicus ) were transferred from 27 to 19 or 35 ° C. Tilapias stop feeding when temperature goes below 15 ° C, and are unable to reproduce below 20 ° C (Sun et al.). High water temperature may pose physiological stress in tilapia, thereby causing cellular injury in kidney and liver as well as reducing the level of erythropoietin, thus leading to a decrease in RBC count (Abdel- Tawwab et al.).

20. The effect of cold temperature on blood parameters of Shizothorax richardsonii showed a decrease in RBC, WBC and haemoglobin content. This decreasing trend of haemoglobin in cold temperatures has also been reported in many species ( Staurnes et al.; Chen et al.). This is because S. richardsonii survive at low temperature by concentration of Na+ and K+ content in plasma. Water temperature decrease, increase the osmotic pressure, increase Na+ and K+ content in plasma.

21. The brain orchestrates an integrated stress response largely following two different neuroendocrine pathways. The first comprises direct neural stimulation of the chromaffin cells in the anterior kidney ( brain-sympathetic-chromaffin cell axis – BSC ) ( Wendelaar Bonga, 1997), resulting in the release of catecholamines into circulation. A second neuroendocrine route, the hypothalamus-pituitary- interrenal (HPI) axis . It starts with the activation of corticotropin releasing factor (CRF) neurons that discharge CRF into the pars distalis of the anterior pituitary. In there, CRF and other peptides (e.g. vasotocin ) stimulate the release of adrenocorticotropic hormone (ACTH) into circulation, which in turn stimulates the production and release of cortisol (the main corticosteroid in teleosts ) from the interrenal cells in the anterior kidney .

22. Those actions include catecholamine-induced responses that are mainly directed towards making energetic substrates readily available to be used by muscle and other tissues to facilitate a behavioural response ( Fabbri & Moon, 2016), and cortisol-mediated changes (predominantly genomic, through the glucocorticoid (GR) and mineralocorticoid (MR) nuclear receptors), acting almost ubiquitously and believed to be directed towards mobilizing and reallocating energy substrates to facilitate adaptation (Faught et al., 2016; Sadoul & Vijayan, 2016).

23. A longer and more sustained activation of the hypothalamic–pituitary– interrenal (HPI) axis, results in plasma elevations of the steroid cortisol in teleosts and chondrosteans , 1a-hydroxycorticosterone in elasmobranchs (Pankhurst 2011) Short-term increases in corticosteroids increase the availability of a variety of energy substrates, Longer-term exposure to elevated cortisol results in suppressive effects on a range of functions including reproduction, growth and immune function

24. Prolonged exposure to high temperature may also induce changes in basal levels of stress hormones . As far as we know, the few studies investigating blood catecholamines have all reported little effect of acclimation temperatures (Milligan et al., 1989; Perry & Reid, 1994). However, catecholamine-induced secondary responses such as the enhancement of blood haemoglobin and haematocrit were often observed in fish exposed to increased temperatures (Houston & DeWilde , 1968; Houston & Cyr, 1974) suggesting that transient catecholamine surges could help the fish to cope with a higher demand for oxygen.

25. Table: Cortisol release as a function of elevated temperature experience Common name (Scientific name) Temperature experience Cortisol release Reference Zebrafish ( Danio rerio ) 10 min - sudden change from 28.5 to 36 °C Increased level Yeh et al., 2013 Black Sea trout ( Salmo trutta labrax ) 30 min - sudden change from 15 to 25 °C Increased level Dengiz Balta et al., 2017 Haddock ( Melanogrammus aeglefinus ) 1 hour - sudden change from 10 to 15 °C Increased level Afonso et al., 2008 Rainbow trout ( Oncorhynchus mykiss ) 1 hour - sudden change from 13 to 25 °C Increased level LeBlanc et al., 2011 Mozambique tilapia ( Oreochromis mossambicus ) 2 hour - sudden change from 22 to 34 °C Increased level Basu et al., 2001 Rohu ( Labeo rohita ) 2 hours - sudden change from 28 to 38 °C Increased level Kumar et al., 2015 Goldfish ( Carassius auratus ) 1 hour - from 19 to 31°C (10°C per hour) Increased level Cockrem et al., 2019

26. Sudden exposure to high temperature is perceived as a stress by fishes, leading to the release of catecholamines and cortisol (LeBlanc et al., 2011; Cockrem et al., 2019). Secondary stress responses are also observed upon acute temperature increase ; glucose and lactate generally rise during acute thermal challenge, along with alterations in blood osmolality and other haematological variables ( Dengiz Balta et al., 2017; Bard & Kieffer, 2019. At the cellular level, Heat Shock Protein (HSPs) release is also modulated by the endocrine stress systems ( Maloyan & Horowitz, 2002; Currie et al., 2008). Briefly, the adrenergic system potentiated the HSP response in red blood cells of rainbow trout Oncorhynchus mykiss ( Walbaum 1792) (Currie et al., 2008), while cortisol inhibited heat stress-induced levels of HSPs ( Basu et al., 2001).

27. THE COMPLEX SYSTEM SHOWING PHYSIOLOGICAL RESPONSE TO STRESS

28. Climate change and spawning Spawning times and locations have evolved to match prevailing physical (such as temperature, salinity, currents) and biological (such as food) conditions that maximize the chances for a larva to survive to become a reproducing adult; or at the very least to minimize potential disruptions caused by unpredictable climate events. Crozier et al. (2008) concluded that climate change is likely to induce strong selection on the date of spawning of Pacific salmon in the Columbia River system. Temperature has also been demonstrated to influence the age of sexual maturity , e.g. Atlantic salmon (Salmo salar ; Jonsson and Jonsson, 2004) and Atlantic cod (Brander, 1994). For these cold water species, warmer conditions lead to earlier (younger) ageat -maturity.

29. TEMPERATURE ON EMBRYONIC DEVELOPMENT AND REPRODUCTION Temperature also has a highly significant effect on the rate of embryonic development. For many species , the rate of embryonic development more than triples for each 10°C increase in temperature (i.e. Q10 >3) ( Rombough 1997). Incubation period is also dependent on egg size, with larger eggs taking longer to develop than small eggs (Pauly and Pullin 1988). Effects of elevated temperature leads to thermal inhibition resulting in activation of the hormonally-mediated stress response. Stress is known to have inhibitory effects on reproduction in fish (Pankhurst and Van Der Kraak 1997; Leatherland et al. 2010). It stimulates activation of an acute catecholamine-mediated response(HPI axis). It has the primary effect of rapidly increasing energy availability and the delivery of O2 to the tissues

30. OCEAN ACIDIFICATION & FISH PHYSIOLOGY Sperm motility of the flounder, Limanda yokohamae , is arrested by mild increases in pCO2 (Inaba et al. 2003) One potential concern is that higher pCO2 may limit the scope for aerobic performance in adults ( Portner and Farrell 2008) Collapse of aerobic scope in association with anomalously high water temperature has been linked to failed migration ( and thus spawning ) in sockeye salmon, Oncorhynchus nerka (Farrell et al. 2008).

31. Experiments with red seabream ( Pagrus major ) demonstrate that larval fish are more sensitive to the effects of acidification with CO2 than to the same pH achieved with mineral acids ( Kikkawa et al. 2004). Fish compensate for acidosis by acid–base equivalent ion transport from the body to the environment, mostly across the branchial epithelium (Claiborne et al. 2002) It can be detrimental to many cellular processes, including protein synthesis , enzymatic function and oxygen transport ( Portner et al. 2004) OCEAN ACIDIFICATION CAN LEAD TO SMALL FISH LOSING THEIR HEARING ABILITY

32. Rising pCO2 is that it can affect the olfactory system of some marine fishes , rendering them unable to distinguish between ecologically important chemical cues (Munday et al. 2009d). Clownfish larvae reared at 1000 ppm CO2 exhibited a broad attraction to any chemical cue presented in binary-choice flume trials and became attracted to chemical cues that they avoided when reared in control seawater

33. Ionic-osmoregulatory function & SALINITY CHANGE Most freshwater fishes are stenohaline and are sensitive to changing environmental salinity (Peterson and Meador 1994) and as such are at risk from increased drought frequency and duration resulting from global climate change (Seager et al. 2007, 2013). Drought conditions result in elevated environmental salinity because of evapoconcentration (Mosley 2015), which oftentimes occurs in warmwater or intermittent streams but may be less frequent in coldwater or perennial systems ( Datry et al. 2014). Because environmental salinity deviates from species-specific optimal salinity , maintenance of hydromineral balance via iono - and osmoregulatory mechanisms becomes increasingly expensive metabolically . These increased energetic costs associated with elevated environmental salinity decrease a fish’s capacity for growth (Morgan and Iwama 1991), reproduction (Hoover et al. 2013), and movement.

34. As environmental salinity increases further, iono - and osmoregulatory mechanisms fail and are no longer capable of maintaining proper osmolality, disrupting cellular activity, and ultimately leading to mortality. Miyazono et al. (2015) found abundance of stenohaline fishes in the Rio Grande River of Texas decreased from the 1970s to the 2010s, a result partially explained by a decreasing trend in heavy precipitation events that previously diluted salinity concentrations, thus resulting in increased salinity in the system.

35. Diadromous and coastal freshwater fishes are also impacted by changing environmental salinities associated with climate change. For instance, inland coastal habitats are experiencing elevated and more variable salinity levels due to rising sea levels and decreased dilution of saltwater from lower freshwater outflows ( Cloern and Jassby 2012). Similar to freshwater habitats affected by more prevalent drought, rising salinity in coastal habitats will disrupt the iono - and osmoregulation of coastal freshwater and diadromous fishes, resulting in reduced growth, reproduction, and survival.

36. Climate change and disease The influence of climate change on fish immune systems primarily occurs when immunocompetence presumably decreased because thermal stress generated a hyperactive immune response , resulting in damaged tissue and cellular debris that elicited an autoimmune disorder (Dittmar et al. 2014). Temperatures exceeding the optimum can also decrease immune function indirectly via effects on the neuroendocrine system , because immunosuppressive cortisol is released during thermal stress ( Weyts et al. 1999). Either of these pathways (autoimmune disorder or immunosuppression) could explain the results of Collazos et al. (1996), who found negative effects of elevated summer temperatures on immunocompetence in Tench ; Tinca tinca when examining seasonal variation in immune function.

37. Climate-related alteration of immune function places fishes at greater susceptibility to parasites and pathogens that result in direct mortality to fishes. For instance, Wegner et al. (2008) observed high (>75%) parasite-induced mortality of Threespine Stickleback during a heat wave in Europe in 2003; in the same year, the bacterium Vibrio anguillarum caused substantial mortality in migrating adult Atlantic Salmon and Brown Trout S. trutta in England (St-Hilaire et al. 2005). Similarly, increasing mortality of Brown Trout over a 25-year warming period in Switzerland was partially explained by increased prevalence of proliferative kidney disease (a myxozoan parasitic disease) (Hari et al. 2006). Greater disease susceptibility can also result in sublethal negative effects on locomotion (Wagner et al. 2005), growth (Tierney et al. 1996), and reproduction ( Rushbrook et al. 2007). These sublethal negative effects can also result in indirect mortality, because diseased fish are more susceptible to predation (Miller et al. 2014).

38. Elevation in ambient temperature could affect transmission essentially in two ways. It could directly enhance parasite metabolism resulting in a higher number of transmission stages being produced, which again would lead to higher parasite fitness and more rapid spread of the disease in a single outbreak. Increase in temperature at either end of the natural period of disease occurrence could extend the length of the transmission season resulting in wider overall spread of the disease in the host population.

39. On the other hand, some diseases could also show the opposite effects with increasing temperature if, for example, their optimal temperature for growth and transmission was lower. For many fish diseases (e.g. furunculosis, koi herpesvirus, spring viraemia of carp), temperature is a key determinant of whether infection results in disease and mortality or immunity and recovery. It is, therefore, highly likely that climate change may affect fish more severely and earlier than homeothermic animals . Increasing freshwater temperature may favour the establishment of introduced non-native aquatic animal species and exotic pathogens , originating in regions with higher ambient temperatures.

40. There is evidence that as seawater temperatures rises , the geographical range of some marine fish species change as they seek to remain at the optimal temperature to maximize growth and thus migrate northwards (Perry et al., 2005). This may be an important pathway for pathogen spread in the marine environment and ultimately to freshwater.

41. The ability of a pathogen to mutate will enable it to respond rapidly to novel opportunities created by climate change, such as the establishment of new host species (Gale et al., 2009). Pathogen evolution lowers the species barrier so new strains are more likely to extend their host range ( Kuiken et al., 2006). Negative strand and segmented genome RNA viruses , such as the family Orthomyxoviridae, have higher mutation rates compared with other viruses (Holland et al., 1982) and thus are more likely to emerge as new diseases or in new hosts. Infectious salmon anaemia virus (ISAV), an orthomyxovirus, appears to have evolved from a wild avirulent ancestor on at least two occasions (Cunningham and Snow, 2000; Nylund et al., 2003). At higher water temperatures, the generation time of bacteria, fungi and parasites with direct lifecycles is shorter ( Gubbins , 2006).

42. Climate change is likely to result in increased acidification in headwater streams , which may result in a decrease in parasite diversity and a loss of trematodes ( Marcogliese , 2001). Meanwhile, lakes are likely to become less acid , and thus parasite diversity may increase ( Marcogliese , 2001). Lower water levels and flow rates will increase the abundance of free-living infective parasite life stages (Johnson et al., 2009).

43. CONCLUSION Climate change is drastically affecting the biotic and abiotic communities of the ecosystem like in ocean, seas, rivers etc. The physiology and the metabolism of the fish is interconnected with abiotic parameters and the habitat. A change in the environmental cues due to climate change can greatly affect the physiology of fish Since the effects are species and region specific more research needed in regard to the tropical environment. More effective governance and adhering to the norms of IPCC nedded to be done for mitigating the impacts of climate change.

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