Seawater acclimation of diploid and triploid brook charr (Salvelinus fontinalis), diploid Arctic charr (Salvelinus alpinus), and their diploid and triploid hybrids

Seawater acclimation of diploid (FF) and triploid (F2F) brook charr Salvelinus fontinalis , diploid (AA) Arctic charr Salvelinus alpinus , and diploid (FA) and triploid (F2A) hybrids between female brook charr and male Arctic charr was investigated. Triploidization of brook charr and the hybrid did not have any effect on the acclimation. Seawater acclimation of the hybrid was achieved during the experimental period and was comparable to that observed in brook charr. Acclimation could not be ascertained in Arctic charr since the level of cortisol, a stress indicator, was still high at the end of the experiment. No relationship between either length or condition factors and plasma osmolality was observed. Elevated plasma cortisol concentrations in Arctic charr and in diploid or triploid hybrids, both in fresh water and sea water, indicate more favourable rearing conditions for brook charr.     

The effect of salty diets and gradual transfer to sea water on osmotic adaptation, gill Na+, K+-ATPase activation, and survival of brook charr, Salvelinus fontinalis, Mitchill

The intensity and duration of the period of osmotic disturbance during introduction of brook charr into sea water were decreased by introducing the fish according to a gradient of salinity over a period of 6 days. Survival in summer increased from 25 to 90% with the use of a salinity gradient. However, kinetics and levels of activation of the gill Na⁺, K⁺-ATPase were not affected by the mode used for introducing brook charr into sea water. Neither was its level of activity modified by the use of a salted diet when the fish were in fresh water. The addition of 8 and 12% of salt to the diet prevented the plasma electrolyte surge of concentrations during the first days in sea water. In very cold water, survival rate was also drastically improved by giving an 8% salted diet during the 6 weeks preceding the introduction into sea water. These results show that both salty diets and exposure to brackish water during 6 days help brook charr face osmotic stress and improve their survival rate when introduced into full-strength sea water. The combined use of these preconditioning strategies might facilitate rearing this species in sea cages or silos.     

Seasonal changes in sea-water tolerance of Arctic charr (Salvelinus alpinus)

Summary Groups of Arctic charr,Salvelinus alpinus, which had been acclimated to water with a salinity of 7 g·l^–1 and natural temperature and photoperiod, were exposed to water with different salinities and temperatures in June, September and February. At a salinity of 15 g·l^–1, plasma osmolality, plasma Na⁺, Cl^–, Mg²⁺ concentrations and the activity of gill Na-K-ATPase were stable, irrespective of temperature and season. In June, the charr were able to regulate blood plasma ionic levels within narrow limits when exposed to a salinity of 34 g·l^–1 (sea water) and a temperature of 8°C. The hypo-osmoregulatory capacity was less, but sufficient if the temperature was only 1°C during the seawater exposure. At the start of the experiment, the gill Na-K-ATPase activity was significantly higher in June than corresponding enzyme activities in September and February. Furthermore, an increase in gill Na-K-ATPase activity during the seawater exposure (8°C) was seen in June. Irrespective of ambient temperature and salinity, no fish died during the June experiments. In September and February, exposure to sea water produced marked increases in plasma osmolality and plasma ion concentrations. There were no changes in gill Na-K-ATPase activity. Consequently, the fish became dehydrated and were moribund after a short period of seawater exposure. Highest mortality was recorded when charr were exposed to winter sea conditions (34 g·l^–1 and 1°C) in February. The results indicate that an increase in daylength induce a hypo-osmoregulatory capacity in the Arctic charr during summer. In fall and winter, however, reduced daylength are accompanied by poor hypo-osmoregulatory capacity. This leads to high mortality as a result of increased electrolyte levels and dehydration.     

Branchial Na(+)K(+)ATPase activity in brook charr (Salvelinus fontinalis): effect of gonadal development in hypo- and hyperosmotic environments

Changes in gill Na(+)K(+)ATPase activity were examined following the transfer of brook charr (Salvelinus fontinalis) from fresh water (FW) to seawater (SW). Gonadal development was altered at the hatching stage using three doses of ionizing radiation (IR): 6.2, 7.8, and 11.4 Gray (Gy). A non-irradiated control group was also included in the experimental set-up. Following 15 and 19 months of growth in FW, assessment of gill activity in regard to gonadal status (sterile vs. mature) and level of IR exposure was realized by conducting two estuarine challenge tests. A first introduction was performed during June (period of highest osmoregulatory capacities for this species) (summer experiment). A second introduction was conducted during October (period of diminished osmoregulatory capacities) (fall experiment). Gill Na(+)K(+)ATPase activity and water content were measured at different times and two FW control samplings were added in October and January. In the summer experiment (June-December), normal gonadal development of female brook charr was related to reduced gill Na(+)K(+)ATPase activity during the spawning period as compared to sterile fish (4.0+/-1.5 and 7.2+/-1.9 micromole Pi. mg protein(-1). hr(-1)) (P<0.0002). Similar results were not observed in FW conditions, implying that a lack of gonadal growth does not initiate a significant advantage when the osmoregulatory system including the gills are not highly in demand, i.e. in a FW environment. Ionizing radiation exposure of < or =11.4 Gy at the hatching stage had no significant negative or positive effect on Na(+)K(+)ATPase activity either in FW or SW conditions.     

In vivo effects of the steroid analogue RU486 on some aspects of intermediary and thyroid metabolism of brook charr, Salvelinus fontinalis.

The glucocorticoid analogue RU486 was administered by intraperitoneal injection to brook charr (Salvelinus fontinalis) to further explore the role of cortisol on aspects of intermediary and thyroid hormone metabolism of the species. RU486 significantly elevated the hepatosomatic index, hepatic G3PDH activity, and hepatic glycogen content, but was without effect on hepatic protein content, hepatic FPBase activity, or plasma glucose concentration. However, the stressor-related increase in plasma glucose concentration that was evident in brook charr 24 h following handling and injection was suppressed in RU486-treated groups. The distribution volume, turnover rates, and metabolic clearance rates of [3H]cortisol were similar in RU486- and vehicle-treated groups. Plasma T3 and T4 concentrations were similar in RU486- and vehicle-treated groups, but hepatic T3 production and hepatic T3 content were lower in RU486-treated fish; TSH had no effect on hepatic T3 content of vehicle-treated brook charr but significantly increased T3 content in the RU486-treated group. These observations support the concept of a role of cortisol in the control of peripheral monodeiodination of T4 in salmonid fish and suggest that RU486 may be a useful drug for evaluating the role of cortisol in fish in vivo.     

PCB disruption of the hypothalamus-pituitary-interrenal axis involves brain glucocorticoid receptor downregulation in anadromous Arctic charr

We examined whether brain glucocorticoid receptor (GR) modulation by polychlorinated biphenyls (PCBs) was involved in the abnormal cortisol response to stress seen in anadromous Arctic charr (Salvelinus alpinus). Fish treated with Aroclor 1254 (0, 1, 10, and 100 mg/kg body mass) were maintained for 5 mo without feeding in the winter to mimic their seasonal fasting cycle, whereas a fed group with 0 and 100 mg/kg Aroclor was maintained for comparison. Fasting elevated plasma cortisol levels and brain GR content but depressed heat shock protein 90 (hsp90) and interrenal cortisol production capacity. Exposure of fasted fish to Aroclor 1254 resulted in a dose-dependent increase in brain total PCB content. This accumulation in fish with high PCB dose was threefold higher in fasted fish compared with fed fish. PCBs depressed plasma cortisol levels but did not affect in vitro interrenal cortisol production capacity in fasted charr. At high PCB dose, the brain GR content was significantly lower in the fasted fish and this corresponded with a lower brain hsp70 and hsp90 content. The elevation of plasma cortisol levels and upregulation of brain GR content may be an important adaptation to extended fasting in anadromous Arctic charr, and this response was disrupted by PCBs. Taken together, the hypothalamus-pituitary-interrenal axis is a target for PCB impact during winter emaciation in anadromous Arctic charr.     

Quantitative genetic analysis of the physiological stress response in three strains of brook charr Salvelinus fontinalis and their hybrids

Three strains [domestic (D), Laval (L) and Rupert (R)] of brook charr Salvelinus fontinalis and their reciprocal hybrids were submitted to transport stress to measure stress resistance. Primary (cortisol) and secondary (glucose, osmolality and haematocrit) stress responses were measured for each cross. Significant heritabilities were observed for both levels of stress response, with mean ± S.E. heritability (h(2)) = 0.60 ± 0.20 for plasma cortisol and 0.61 ± 0.20 for plasma glucose. There were strain differences whereby the R strain was the least sensitive to stress at the primary and secondary levels. No heterosis was detected, and only one case of outbreeding depression was present. The outbreeding depression was observed in the D(♀) R(♂) hybrid, which had a 27% increase of plasma glucose compared to parental strains. The D(♀) R(♂) and R(♀) L(♂) hybrids had more pronounced variations (increase or decrease) in plasma osmolality than their respective parental strains, but these variations were difficult to relate definitively with the potential secondary stress response. These results indicate a strong potential for genetic improvement in the stress response to transport with the use of purebred crosses while hybridization has little value in this regard.     

Plasma thyroxine and cortisol profiles and gill and kidney Na+/K+-ATPase and SDH activities during acclimation of the catfish Heteropneustes fossilis (bloch) to higher salinity, with special reference to the effects of exogenous cortisol on hypo-osmoregulatory ability of the catfish

When the stenohaline catfish Heteropneustes fossilis was transferred from fresh water (FW) to 30% seawater (SW), the Na(+)/K(+)-ATPase activity significantly increased in the kidney, while in gills it remained more or less constant. A reverse pattern was observed for succinic dehydrogenase (SDH) activity inasmuch as it significantly increased in gills and remained unchanged in the kidney. Plasma osmolality significantly increased within 3 days of transfer to 30% SW and remained significantly higher throughout the duration of experiment. These results suggest that catfish gills may not be able to reverse their function from salt uptake in FW to salt excretion at higher salinity, and that the elimination of monovalent as well as divalent ions is performed by the kidney but not the gills. The significant decline in plasma cortisol (F) levels following transfer to higher salinity may not be due to reduced production but rather to an enhanced utilization and clearance rate, a conclusion supported by the fact that exogenous administration of cortisol acetate (FA) resulted in significant increases in branchial and renal Na(+)/K(+)-ATPase in FW and 30% SW. FA also improved the plasma osmotic regulatory ability of the catfish, possibly due to a change in branchial function from salt-absorption to salt excretion, as was evident from a significant increase in branchial Na(+)/K(+)-ATPase activity in the fish in 30% SW pretreated with FA for 5 days. Consistently higher levels of plasma thyroxine (T4) following transfer to higher salinity suggest the involvement of this hormone at higher salinity.     

Heat shock protein (Hsp70) induced by a mild heat shock slightly moderates plasma osmolarity increases upon salinity transfer in rainbow trout (Oncorhynchus mykiss)

We have investigated whether mild heat shock, and resulting Hsp70 expression, can confer cross-protection against the stress associated with transfer from freshwater (FW) to seawater (SW) in juvenile rainbow trout (Oncorhynchus mykiss). In experimental Series I, juvenile trout reared in FW were transferred from 13.5 degrees C to 25.5 degrees C in FW, held for 2 h, returned to 13.5 degrees C for 12 h, and then transferred to 32 ppt SW at 13.5 degrees C. Branchial Hsp70 increased approximately 10-fold in the heat-shocked fish relative to the control by the end of recovery and remained high 2, 8, and 24 h post-salinity transfer. However, no clear differences could be detected in blood parameters (blood hemoglobin, hematocrit, MCHC, plasma Na(+) and plasma osmolarity) or muscle water content between heat-shocked and sham-shocked fish in SW at any sampling interval (0, 2, 8, 24, 48, 120, 240 and 360 h post-SW transfer). In experimental Series II, trout acclimated to 8 degrees C were heat-shocked at 22 degrees C for 2 h, allowed to recover 18 h, and exposed to a more severe salinity transfer (either 36 or 45 ppt) than in Series I. Branchial Hsp70 levels increased approximately 6-fold in heat-shocked fish, but had declined to baseline after 120 h in SW. Plasma osmolarity and chloride increased in both groups upon transfer to 36 ppt; however, the increase was significantly less in heat-shocked fish when compared to the increase observed in sham-shocked fish at 24 h. No significant differences could be detected in branchial Na(+)/K(+)-ATPase activity or Na(+)/K(+)-ATPase alpha1a and alpha1b mRNA expression between the two groups. Our data indicate that a mild temperature shock has only modest effects on the ability of rainbow trout to resist osmotic stress during FW to SW transfer.     

The Effect of Acute Stress and Temperature on Plasma Cortisol and ion Concentrations and Growth of Lake Inari Arctic Charr, Salvelinus Alpinus

One year old, individually tagged Lake Inari Arctic charr, Salvelinus alpinus, were reared at three constant temperatures, 10.3°C, 14.1°C and 18.1°C, over four weeks. Blood samples were collected from a group of unstressed fish after the cultivation period at the same time as another group of fish were subjected to acute handling stress treatment (2min netting in air and 40min (± 20min) recovery period in water). Plasma cortisol, calcium, sodium, potassium and chloride concentrations were measured on both groups. To study the effect of minor daily temperature fluctuations on the stress response of Arctic charr, two additional daily fluctuating temperature (14 ± 1°C, 18 ± 1°C) treatments were established. The samples were taken in the same manner as those in the constant temperature treatments. Growth was fastest at 10.3–14.1°C and clearly lower at 18.1°C. Pre-stress plasma cortisol levels were low but increased slightly with increasing temperature. After stressor treatment, the cortisol concentrations of Arctic charr were clearly higher in all temperature treatments but there were no significant differences in plasma cortisol concentrations among temperatures. Plasma calcium levels increased during the stress treatment but temperature did not modulate this effect. The plasma potassium concentrations declined at 14.1–18.1°C after acute stress but the response was not affected by temperature within this range. The concentrations of sodium and chloride were unaffected by acute stress. Temperatures of 10.3–18.1°C and fluctuating temperature treatments had no influence on any plasma ion concentrations. Arctic charr were able to maintain the plasma ion concentrations in fresh water at 10.3–18.1°C and after acute stress treatment. Results indicate that the optimum temperature for growth of Arctic charr has little to do with the plasma ion concentrations or the ability to maintain those concentrations after short-term stress. The plasma cortisol responses further indicate that the optimum temperature for growth of Arctic charr is not related to the suppressed ability to react to an acute handling stressor. Temperature fluctuations did not cause significant differences in cortisol levels when compared with constant temperatures.     

Expression of warm temperature acclimation-related protein 65-kDa (Wap65) mRNA, and physiological changes with increasing water temperature in black porgy, Acanthopagrus schlegeli

We isolated the warm temperature acclimation-related protein 65-kDa (Wap65) cDNA from the liver of black porgy and investigated the expression by increasing water temperature in black porgy, Acanthopagrus schlegeli. Black porgy Wap65 full-length cDNA consists of 1,338 nucleotides, including an open reading frame, predicted to encode a protein of 425 amino acids and showed high homology to pufferfish (79%), Medaka (73%), carp (70%), and goldfish (68%) Wap65. Increase in water temperature (20 degrees C --> 30 degrees C; 1 degrees C/day) induced the rise of Wap65 mRNA expression in liver of black porgy. Also, the levels of cortisol and glucose in plasma were significantly higher at 30 degrees C than at 20 degrees C. To determine the high water temperature stressor specificity of the induction of Wap65, black porgy were transferred from seawater (SW) to freshwater (FW) for 24 hr. Wap65 expression was not detected when the fish were transferred from SW to FW (in fish transferred from SW to FW), although the levels of cortisol and glucose in plasma were increased. These results suggest that increase in Wap65 gene is related to high water temperature stress and play important roles in high water temperature environment of black porgy.     

Influence of spring and summer water temperature on brook charr, Salvelinus fontinalis, growth and age structure in the Ford River, Michigan

Synopsis The influence of late spring and summer water temperatures on brook charr, Salvelinus fontinalis, growth and age structure was evaluated from 1984 to 1991 in the Ford River, Michigan. Temperature was monitored and brook charr sampled for vital statistics from late May through September using fyke nets and weirs at four locations within a 25.8 km section of stream. Scale analysis was used to determine captured brook charr age, past length at age and relative annual growth rates. Late spring and summer water temperature patterns varied between years with the greatest variability occurring in May and June. Age and size structure also varied between years and was significantly related to temperature. Years with cooler late spring and summer temperature patterns were dominated by older (age 2 and 3), larger brook charr, while years with warmer spring and summer temperature patterns were dominated by younger (age 1), smaller brook charr. Spring and summer temperature did not appear to have a significant effect on the growth of age 0 or age 1 brook charr. However, temperature was negatively related to brook charr growth from age 2 on. As spring and summer water temperatures are critical to brook charr growth and survival, it is important that a streams thermal regime be considered when establishing management goals for this species.     

Effects of environmental water salinity on blood acid-base status in juvenile turbot (Scophthalmus maximus L.)

The time courses of extracellular ionic and acid-base adjustments were studied in juvenile turbot (Scophthalmus maximus) following a decrease of water salinity, either abruptly from 32 to 10%. or after a first step (4 weeks) in 19%. salinity followed by a direct transfer to 10%. brackish water (BW). Net exchanges of acid-base equivalents with the external water were also determined after transfer from 32%. SW to 10%. BW. Direct transfer from seawater (SW) to 10%. BW induced a transient decrease in plasma osmolarity, plasma sodium and chloride concentrations, associated with a marked and transient metabolic alkalosis in the blood. A significant net outflux of acidic equivalents was also measured only during the first day in BW. Four weeks preadaptation in 19%. BW reduced the intensity of the osmotic disturbances elicited by a subsequent abrupt transfer to 10%. BW. These ionic readjustments were also coupled with minimal acid-base changes, of lesser magnitude than those described after directly from SW to 10%. BW.     

Effects of exogenous cortisol and seawater adaptation on thyroid hormone receptors in the smolt stage of the sockeye salmon,Oncorhynchus nerka

The objective of this investigation was to quantify how thyroid hormone receptors of the sockeye salmon, Oncorhynchus nerka, respond to salinity changes from freshwater (FW) to seawater (SW) conditions. Thyroid hormone receptors (TRs) mRNA and protein expressions levels significantly increased when the fish were transferred from FW to SW, and the plasma T₃ and T₄ levels were significantly highest at 50 % SW and then maintained as control. Moreover, these parameters were significantly lower in the cortisol-injected groups than in the control. Hence, TRs, T₃, and T₄ may play a role in SW adaptation, when the fish migrate from FW to SW environments. We showed a negative correlation between cortisol and thyroid hormone levels, and a significant increase in plasma K⁺ levels in the kidney when the fish were transferred to SW, with levels being significantly lower in the cortisol-injected group. Hence, cortisol appears to be a stress hormone, and the plasma Na⁺ and Cl^- levels significantly increased when the fish were transferred to SW, with levels being significantly lower in the cortisol-injected group. These results indicate that cortisol modulates ion transportation in the plasma.     

Prolactin regulation in the coho salmon,Oncorhynchus kisutch

Summary Parr and smolt sea water acclimated coho salmon,Oncorhynchus kisutch were subjected to gradual and direct transfers to fresh water. Plasma osmotic pressure, Na⁺, K⁺, Ca⁺⁺ and Mg⁺⁺ were similar in freshwater (FW) fish and seawater (SW) transferred controls for the 24 h following transfer. In spite of the similarity in osmotic pressure and ion levels, plasma cortisol concentrations were significantly increased immediately following salinity change while both pituitary and plasma prolactin decreased indicating enhanced secretion by the pituitary and clearance from the blood. In vitro experiments showed greater incorporation of tritiated leucine into prolactin (PRL) cells immediately after transfer to FW while prolactin injections into intact fish lowered activity in rostral pars distalis (RPD) cells as measured by the same technique, providing evidence of hormonal feedback. These experiments show that the increased synthesis and release of PRL that occurs in coho following movement into FW is not obviously correlated with plasma osmotic pressure, Na⁺ or Ca⁺⁺ concentrations as has been observed in other species of teleosts.Abbreviations FW freshwater - SW seawater - PRL prolactin - RPD rostral pars distalis     

Lipids as energy source during salinity acclimation in the euryhaline crab Chasmagnathus granulata dana, 1851 (crustacea-grapsidae)

Lipids seem to be the major energy store in crustaceans. Moreover, they are extremely important in maintaining structural and physiological integrity of cellular and sub cellular membranes. During salinity adaptation, energy-demanding mechanisms for hemolymph osmotic and ionic regulation are activated. Thus, the main goal of this work was to verify the possible involvement of lipids as an energy source in the osmotic adaptation process. The estuarine crab Chasmagnathus granulata was captured and acclimated to salt water at 20 per thousand salinity and 20 +/- 2 degrees C, for 30 days. After acclimation, crabs were divided into groups of ten and transferred to fresh water (0 per thousand ), salt water at 40 per thousand salinity, or maintained in salt water at 20 per thousand salinity (control group), without feeding. Before and seven days after the salinity change, wet weight and lipid concentration in gills, muscle, hepatopancreas, and hemolymph were determined according to the colorimetric assay of sulphophosphovanilin. Results show that hepatopancreas lipids were not mobilized during osmotic stress regulation. Gill and muscle lipids were significantly lower in crabs subjected to hypo-osmotic stress than those subjected to the hyper-osmotic stress or maintained at the control salinity. Our results point to the occurrence of lipid mobilization and involvement of these compounds in the osmotic acclimation process in C. granulata, but with differences between tissues and the osmotic shock (hypo or hyper) considered.     

Plasma cortisol and osmoregulatory changes in sockeye salmon transferred to sea water: Comparison between successful and unsuccessful adaptation

Gill Na⁺-K⁺-ATPase activities, haematocrits, condition factors, plasma osmolarities, cortisol, chloride and sodium concentrations were measured in sockeye salmon ( Oncorhynchus nerka ) transferred rapidly from fresh water to sea water. Comparisons were made between salmon that successfully adapted to sea water and salmon that failed to adapt. In salmon that successfully adapted to sea water there was a brief but large fluctuation in cortisol, and plasma ionic concentrations rose initially but were regulated after 24–48 h. In salmon that failed to adapt to sea water, cortisol remained elevated, haematocrit increased, plasma ionic concentrations were not regulated and the salmon became severely dehydrated and eventually died. The results are discussed with respect to physiological stress and seawater adaptation.     

Chemical Alarm Signals Enhance Survival of Brook Charr (Salvelinus fontinalis) During Encounters with Predatory Chain Pickerel (Esox niger)

A diversity of aquatic organisms release chemical alarm signals when attacked or captured by a predator. These alarm signals are thought to warn other conspecifics of danger and, consequently, may benefit receivers by increasing their survival. Here we experimentally investigated the differences in behaviour and survival of hatchery-reared juvenile brook charr Salvelinus fontinalis that had been exposed to either brook charr skin extract (experimental treatment) or a control of swordtail skin extract (control treatment). Charr exposed to conspecific skin extract exhibited a significant reduction in movement and/or altered their foraging behaviour in the laboratory when compared with charr exposed to swordtail skin extract. We also exposed charr to either water conditioned by a single brook charr disturbed by a predatory bird model or water conditioned by a single undisturbed brook charr. Charr exposed to disturbance signals reduced activity significantly more than charr exposed to chemical stimuli from undisturbed charr. These results demonstrate the existence of both damage-released alarm signals and disturbance signals in brook charr. Wild brook charr also responded to damage-released alarm cues under natural conditions. Charr avoided areas of a stream with minnow traps labelled with conspecific alarm cues vs. control cues. During staged encounters with chain pickerel Esox niger in the laboratory, predator-naive charr fry were better able to evade the predator if they were previously warned by an alarm signal, thus suggesting a survival benefit to receivers. Collectively, these results demonstrate that the presence of alarm signals in brook charr has important implications for understanding predator–prey interactions.     

Studies on the relationship between osmotic or ionic regulation and thyroid gland activity in two salmonid fishes, Salmo gairdneri Richardson and Oncorhynchus kisutch Walbaum

In freshwater-acclimated rainbow trout a single intraperitoneal injection of ovine TSH significantly elevated plasma thyroxine (T₄) levels within 1 h after the injection. In seawater adapted trout the increase in T₄ after TSH-treatment was not evident until 6 h after the injection. TSH caused a transient fall in plasma Na⁺ and Cl^- between 3 h and 9 h after the injection in seawater-adapted fish and plasma Na⁺ was lowered in freshwater-adapted trout 24 h after the injection. Although there were clear histological changes in the thyroid gland of freshwater-adapted trout after TSH-injection, no such changes were evident in seawater-adapted fish.
Plasma thyroid hormone levels and thyroid histology in freshwater-adapted rainbow trout and coho salmon transferred to sea water, and seawater-adapted trout transferred to fresh water showed no consistent changes compared with controls.
The data are interpreted to indicate that although ambient salinity may have indirect effects on thyroid activity there is no direct involvement in ionic or osmotic regulation in the two species.