Physiological studies on supercooled killifish (Fundulus heteroclitus) I. Serum inorganic constituents in relation to osmotic and ionic regulation at subzero temperatures

Abstract

Physiochemical properties (serum osmolality and blood pH), serum inorganic ions (sodium, potassium, calcium, magnesium, chloride, phosphate and bicarbonate) and tissue water were studied in parallel groups of adult male Fundulus heteroclitus acclimated to various temperatures (30"C, 20°C, 10°C, 4"C, 2"C, -1°C and -1.5"C) in salt water under otherwise constant laboratory conditions. When the acclimation temperature was lowered from 20°C to -1.5"C, serum osmolality increased by 20%. This increase was not indicative of osmoregulatory failure, however, since the proportion of total serum osmolality accounted for by inorganic electrolytes dropped from 98% at 20°C to 93% at -1.5"C. Serum electrolytes such as sodium, chloride, calcium, magnesium and bicarbonate increased in the subzero cold by 12%, 17%, 30%, 33% and 11% respectively whereas serum potassium and inorganic phosphate levels were unchanged. Blood pH was significantly higher at 10°C than at any other temperature. The water content of liver, testes and muscle decreased by 8% in the subzero cold. These changes in serum electrolytes and tissue water did not indicate osmoregulatory failure, however, since the new levels, once established, were maintained as long as the fish were alive. Although osmotic and ionic regulation were not as effective in the cold, they were by n o means so poor as to cause death by osmotic imbalance.Two common causes of death jn fish at low temperatures are osmoregulatory failure and, at temperatures below freezing, the destruction of tissues by the formation of ice (Fry, '67). However, not all fish die in the cold and many can survive at subzero temperatures. For example, investigations by Scholander et al. ('57) and Umminger ('67) showed that the killifish, Fundulus heteroclitus, could survive the subzero cold in a supercooled state. To gain deeper insight into the mechanisms permitting survival of the killifish at subzero temperatures, then, at least two aspects of cold acclimation should be studied : the ability to osmoregulate in the cold and the means to avoid the formation of ice in the supercooled blood.The present paper deals with osmotic and ionic regulation by the killifish in the cold whereas a paper to follow will deal with the problem of survival in a supercooled state. However, in examining both aspects of survival at subzero temperatures, the same approach has been used: a detailed chemical analysis of the serum.J, EXP. ZOOL., 172: 283-302.In most cases, chemical analyses of both inorganic and organic constituents were made on the same serum sample. In the present paper, however, only the inorganic components of the serum are discussed since they have the greatest bearing on the problem of osmoregulation. In the paper to follow, data on the organic serum constituents are presented to complete the study of the serum chemistry at subzero temperatures. MATERIALS AND METHODSAdult male F. heteroclitus, captured at small inlets of Long Island Sound in the vicinity of New Haven, Connecticut, were maintained on an 8-ho...

Environmental influences on regulation of blood plasma/serum components in teleost fishes: a review

“…Many species also add organic molecules, colligative or non-colligative, to their plasma at such low ambient temperatures. This was demonstrated in Fundulus heteroclitus in SW (Umminger 1969a), an estuarine and nearshore marine species that also has FW populations. When individuals of this species were acclimated in SW to a temperature of 20°C the plasma/ serum osmolality was found to be 364 mOsm kg -1 .…”

“…This takes us back to the old concept that marine species show increased ionic and osmotic concentrations at low water temperatures, while freshwater teleost fishes show reduced plasma ionic and osmotic concentrations at low water temperatures. The concept is attributed to a number of investigators (Eliassen et al 1960, in Umminger 1969a, 1971dHouston and Madden 1968;Prosser et al 1970). However, many exceptions have been found to these generalizations, and they were considered to be inconsistent with existing information, especially for freshwater fishes (Burton 1986b).…”

Determinants of otolith chemistry seasonal variation in the composition of blood plasma, endolymph and otoliths of bearded rock cod Pseudophycis barbatus

“…He did not consider the relative glucose levels of fish in the fed and unfed state. In addition to capture-related stress, it is important to consider environmental stress (Wedemeyer 1981), temperature (Umminger 1969 (Lehninger 1975); this effect is clearly illustrated in research on the sand dab Limanda limanda (Fletcher 1984).…”

Relationship of season, thermal loading and red‐sore disease with various haematological parameters in Micropterus salmoides

“…This finding was expected and compares favourably with reports of other investigators (Palacios et al, 1972;Holmes 8c Donaldson, 1969). Umminger (1969Umminger ( , 1970 has presented evidence of a decrease in levels of sodium in response to reduced temperatures; our own observations in this regard certainly do not indicate such changes from winter to summer. However, we can see a difference between locations within a single season.…”