One reason to keep feeding a little , if they will eat is to stop what Bill describes ... "Some fish will even utilize body protein for energy production
when fat reserves are depleted." On this point take note that the usage by many fish species of their lipid (fat) reserves to a large extent can lead to death.
Here is a past note on HSB reaction to cold and its effects on body metabolism and function leading to death.
It is believed that the lipid composition in the fish muscle plays a vital role in the ability of fish to adapt from one temperature to another . Due to cellular disfunction from low lipids the fish lock up stiffen and heart and respiration stop.
For example, the Nile tilapia Oreochromis niloticus does not store excess lipids in the musculature but rather relies on visceral deposits that it is incapable of mobilizing at low temperatures, which results in high mortalities between 8°C and 6.5°C (Satoh et al. 1984).
The dynamics of lipid composition of cells occurs in order to maintain a constant fluid matrix for enzymes associated with membranes (Greene and
Selivonchick 1990). Different species of fish differ in their patterns of fat deposition and mobilization, which in turn affects the temperature range in
which the species can grow and survive. the ability of a fish to alter its lipid composition when placed in colder water is one factor that determines survival.
In these fish, the fat apparently hardens in the colder water, causing the fat-impregnated muscles to stiffen and the fish to become exhausted and lose movement.
Physiologically, fish are affected by variations in water temperature in two ways (Hochachka and Somero 1984). First, temperature
determines the rate of chemical reactions, and secondly, temperature dictates the point of equilibrium between the formation and disruption
of the macromolecular structures in biological membranes. Structural flexibility, therefore, is a requirement for integrity of biological membranes
(Hazel 1993). Cold temperatures constrain this flexibility and, as a result, stabilize less active conformations.
The rate of resistance to lower temperatures is governed in part by the rate of metabolism, which is depressed at lower environmental temperatures.
See this thread
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=111414&page=1For ease of reference -- one post
Death of fish when oxygen is depleted and concentrations of carbon
dioxide build up beneath snow-covered ice is a common phenomenon
in the North Central States (Greenbank, 1945; Bennett, 1948b; Cooper
and Washburn, 1949). For the Marion County farm ponds information
on .occurrence of winterkill has been gathered from two sources: from
farmers and others who observed numbers of dead fish in ponds following
the breakup of ice, and from pond histories that indicate a sudden mass
disappearance of bass, of .bluegills, or of both. While in many cases there
is no evidence as to the time of year when such fish disappeared, heavy
mortality during the summer was observed by *he pond owners only once
(Pond 16) while winterkill was observed frequently. The chances of mass
mortality of fish being unobserved are probably greater in the win,ter than
the summer.
It appears that fish populations in 31 of the ponds suffered winterkill
(Table 6). In 15 ponds bass were eliminated but some bluegills survived;
in two ponds the reverse was true, with bluegills winterkilled while some
bass survived. The differential in mortality between these two species may
represent a difference in tolerance to low oxygen levels (though Cooper
and Washrburn, 1949, found none), but more likely it may represent
a difference in location within the pond during wintertime and ability
of some individuals to iocate and utilize pockets of water containing suf-
ficient oxygen for survival.
Complete kills of both bass and bluegills occurred in 18 ponds. Thirteen
of the 18 ponds also contained bullheads, and these always survived in
some numbers.
Some ponds winterkill repeatedly, as is shown by the frequency of some
pond numbers in Table 6.
T^BLE &--Known or suspected winterkills of fish in Iowa farm fish ponds
Species eliminated by kill Pond numbers
Bass, but not bluegills ..........................
3, 19, 19, 20, 24, 24, 29, 30, 32,
32, 35, 37, 40, 47, 48, 49, 49, 49,
50, 59
Bluegills, but not bass ..........................
3, 27
Bass and bluegills ...............................
9, 10, 11, 15, 16, 16, 16, 16, 20,
23, 27, 31, 35, 36, 39, 40, 41, 47,
49, 55, 56
Some bass and some bluegills ...................
94, 15, 25, 37, 45
Winterkill is believed to be a major factor in the lack of population
balance and success of Iowa ponds. The population remaining after an
incomplete kill is often very different than that presen.t before, and the
change is usually unfavorable for .angling (Bennett, 1948a). Of the ponds
which winterkilled, one-half had Ibeen listed as muddy with colloidal clay,
and one-third were known to have had low water levels going into the
winter season.
Data sources used for analysis of geographic variations in acute temperature preferences of fishes.
Redear sunfish, Lepomis microlophm'
Hill et al. (1975) Oklahoma 16.0-26.0
Still others, particularly the centrarchids, showed
occasional low thermal responsiveness. Fishes
continued to seek increased temperatures until
they succumbed due to physiological inability
to adjust to a rapid increase in temperature in
a steep gradient.
When raising hybrid striped bass in cages, several producers have reported sudden losses of hybrids when the water temperature rapidly decreased by several degrees in a relatively short period of time (Valenti 1989; A. M. Kelly and C. C. Kohler, personal observation). The rapid onset of cold temperatures has been reported as the cause of death in several species of fish (Verril 1901; Storey 1937; Galloway 1941; Gunther 1941; Ash et al. 1974; Coutant 1977; Mitchell 1990). It is believed that the lipid composition in the fish muscle plays a vital role in the ability of fish to adapt from one temperature to another (Hazel 1984; Greene and Selivonchick 1987; Henderson and Tocher 1987). Phospholipids are the class of lipids in which the most obvious changes occur. As environmental temperatures decrease, the invariable response is an increase in fatty acid unsaturation (Johnston and Roots 1964; Caldwell and Vernberg 1970; Hazel 1979; Cossins and Prosser 1982). Conversely, as ambient temperatures increase, phospholipid saturation must also increase to avoid excess fluidity. The dynamics of lipid composition of cells occurs in order to maintain a constant fluid matrix for enzymes associated with membranes (Greene and Selivonchick 1990). Different species of fish differ in their patterns of fat deposition and mobilization, which in turn affects the temperature range in which the species can grow and survive. For example, the Nile tilapia Oreochromis niloticus does not store excess lipids in the musculature but rather relies on visceral deposits that it is incapable of mobilizing at low temperatures, which results in high mortalities between 8°C and 6.5°C (Satoh et al. 1984). Viola et al. (1988) demonstrated that the common carp Cyprinus carpio, which is capable of mobilizing lipids from muscular and visceral deposits, is able to survive to 4.5°C under the same conditions.
The amount of unsaturated fatty acids in the muscle is believed to affect a fish's ability to tolerate lower temperatures (Hoar and Dorchester 1949; Hoar and Cottle 1952a, 1952b). In general, the tissue temperature of fish is within 1°C of the ambient water temperature (Carey et al. 1971; Reynolds et al. 1976). Physiologically, fish are affected by variations in water temperature in two ways (Hochachka and Somero 1984). First, temperature determines the rate of chemical reactions, and secondly, temperature dictates the point of equilibrium between the formation and disruption of the macromolecular structures in biological membranes. Structural flexibility, therefore, is a requirement for integrity of biological membranes (Hazel 1993). Cold temperatures constrain this flexibility and, as a result, stabilize less active conformations. The rate of increase in the ability of fish to tolerate higher temperatures usually requires less than 24 h at temperatures above 20°C, whereas the gain in resistance to lower temperatures is a much slower process, requiring up to 20 d in some species (Doudoroff 1942; Brett 1944). The rate of resistance to lower temperatures is governed in part by the rate of metabolism, which is depressed at lower environmental temperatures. The simulated cold front in this study resulted in higher mortalities
Diets influence the fatty acid composition in several species of fish (Henderson and Tocher 1987; Lovell 1989; Seo et al. 1994), and the ability of a fish to alter its lipid composition when placed in colder water is one factor that determines survival. For example, summer harvest syndrome is an anomaly seen in goldfish Carassius auratus when they are harvested in the summer and placed in tanks containing water that is colder than the pond water (Mitchell 1990). The death of these fish is thought to be a result of the fat that the goldfish consume or produce (Mitchell 1990). Goldfish with high concentrations of saturated body fat are less tolerant of temperature change than fish with high concentrations of unsaturated body fat. Similarly, rainbow trout Oncorhynhcus mykiss that have been fed diets high in saturated fats stiffen and die when placed in cold water (Mitchell 1990). In these fish, the fat apparently hardens in the colder water, causing the fat-impregnated muscles to stiffen and the fish to become exhausted and lose movement.
Although it has been hypothesized that temperature is closely linked to membrane composition, relatively few studies have been conducted to determine if a correlation exists between lipid composition and cold tolerance. This study was designed to determine the effect of a sudden temperature change (a simulated cold front) on striped bass, white bass, and their hybrids fed either a natural or prepared diet, as well as to determine their lower incipient lethal temperature. The association of fatty acid composition and unsaturated: saturated fatty acid ratios in these fish were examined with respect to their tolerance to cold.
We demonstrated that diet-induced muscle fatty acid composition directly affects cold tolerance of striped bass, white bass, and their hybrids. Fish fed fathead minnows had fatty acid ratios 1025% higher than fish fed a prepared diet. When subjected to a simulated cold front, all groups of fish fed the prepared diet suffered high mortality (5090%) whereas the groups fed the natural diet experienced zero mortalities. The LILT was also higher for fish fed the prepared diet.
Fish deaths due to cold temperatures have frequently been reported. It is generally believed that deaths arise from the rapidity of dropping temperatures whereby the fish are unable to acclimate to the lower temperature despite being within their biokinetic range. It is consequently critical especially in autumn to feed fish of the genus Morone, and possibly other genera, a diet that is relatively low in saturated fats when they are confined to surface waters in cages or pens.
