Diet variation of a generalist fish predator,grey snapper Lutjanus griseus,across an estuarine gradient: trade‐offs of quantity for quality?

This study examined diet, prey quality and growth for a generalist fish predator, grey snapper Lutjanus griseus, at five sites across an estuarine gradient in the Loxahatchee River estuary, Florida, U.S.A. Lutjanus griseus diets shifted from dominance by low quality, intertidal crabs upstream to an increased reliance on higher quality shrimp, fishes and benthic crabs downstream. Frequency of L. griseus with empty stomachs was higher at downstream sites. Lutjanus griseus growth rates did not vary among sites. Results indicate that L. griseus may be able to compensate for lower quality prey upstream by consuming more, and thus individuals are able to maintain similar levels of energy balance and growth rates across the estuarine gradient. Elucidating mechanisms, such as compensatory feeding, that enable generalist species to remain successful across habitat conditions are critical to understanding their organismal ecology and may facilitate predictions about the response of generalists to landscape alteration.     

两品系蒙古裸腹溞种群补偿生长及适宜食物密度

研究了两品系蒙古裸腹溞(晋南品系和内蒙品系)继饥饿后的补偿生长及其生长发育的适宜食物密度。结果表明,两品系蒙古裸腹溞生长发育的最适食物——篕∏蛟迕芏染?50×104/mL。对两品系蒙古裸腹溞而言,饥饿0.5d的蒙古裸腹溞有全补偿生长,饥饿1~2d有部分补偿生长现象,饥饿超过3d已没有补偿生长。可以认为,蒙古裸腹溞仅在短时间饥饿时有补偿生长现象的发生。     

Thermal preference of Arctic charr, <Emphasis Type="Italic">Salvelinus alpinus</Emphasis>, and brown trout, <Emphasis Type="Italic">Salmo trutta</Emphasis> – implications for their niche segregation

This study tested a new experimental apparatus to estimate thermal preferences of fish. The apparatus was designed to minimise the effect of the thermal history of the fish and allow for easy feeding. The set-up consisted of two connected sections of an aquarium, both receiving an excess of food, with slightly different water temperatures. Initially, the fish spent most of its time in one of the sections, but when the temperatures were slowly increased (or decreased), the fish spent increasingly more time in the other. The temperature at which the fish spent equal time in both sections was defined as the preferred temperature. Brown trout, Salmo trutta, preferred the reported optimal temperature for growth of the species. However, Arctic charr, Salvelinus alpinus, selected a significantly lower temperature than its optimal temperature for growth and thus contradicted the general view of good correlation between the optimal temperature for growth and preferred temperature of fish. The reason for this may be that charr is optimising its growth efficiency instead of its growth rate. Individuals that utilise a limited resource in an optimal way, by selecting a temperature where the growth efficiency is maximised, will possibly be favoured. Several factors affect the distribution of fish in lakes, but the difference in thermal preference between charr and trout might partly explain the frequently observed niche segregation of these two species in Scandinavian lakes.     

Enumeration and structural assessment of peritoneal macrophages during progressive protein deficiency in rats

The effects of protein malnutrition on responsiveness of macrophages to proteosepeptone stimulation and on their chemical composition were investigated. Relative number of resident macrophages in rat peritoneal cavity was reduced by about 50 % during 4 weeks on 3 % protein diet. Similarly, decreased migration capacity of the circulating macrophages to the peritoneal exudate in response to the stimulant, was observed in protein-fasted rat compared to that in the 20 % protein-fed group. Further, the chemical composition of the isolated elicited cells was determined. Total proteins, sugars, lipids and nucleic acids were significantly low in the cells isolated from protein-deficient animals, though the cell size was not affected. However, cholesterol: phospholipid molar ratios were distinctly higher than that in control and increased progressively in the 3 and 8 % protein-fed animals. The implications of these structural changes in macrophages on their functional capability are discussed     

Induced thermotolerance and tissue Hsc70 in juvenile coho salmon, Oncorhynchus kisutch

We examined Hsc70 in gill, liver and caudal fin from coho salmon ( Oncorhynchus kisutch ) before (ambient, ~12 °C) and after a sublethal heat shock of 25 °C for 1 h. Increased levels were observed for at least 48 h in all three tissues. Attempts to demonstrate isoforms of this heat-shock protein were not successful using four different antibodies. However, one of these antibodies recognized isoforms in brine shrimp and oysters, two organisms in which the heat-shock response has been well characterized. Extracts of those organisms and coho salmon tissues were run on the same gels and evaluated on the same Western blots, at the same time. We believe that our results provide a reliable account of Hsc70 in these fish under these conditions. Limited experiments showed that induced thermotolerance was achieved in these coho salmon, lasting for about 1 week after the sublethal heat shock. These data suggest that increased levels of Hsc70 are correlated with induced thermotolerance in these fish.     

Chronic Food Deprivation Decreases Extracellular Dopamine in the Nucleus Accumbens: Implications for a Possible Neurochemical Link Between Weight Loss and Drug Abuse

In rats reduced to 80% of normal body weight (n=9), the basal levels of extracellular dopamine (DA) in the nucleus accumbens (NAC), as determined by microdialysis, decreased significantly to 33 % (mean ± SEM) of their normal baseline (p<.01). Basal extracellullar DA did not change significantly over a matching 3-week period in controls (n=7). No changes were observed in NAC serotonin after weight reduction. These results indicate that parts of the mesolimbic DA system are depressed in underweight rats. The observed decrease in basal DA may be responsible for a variety of behavioral changes observed in undernourished humans and animals including the tendency to eat and gain weight when food becomes available. Given that DA can be released in the NAC when rats self-inject drugs of abuse, the present findings may help explain why animals increase drug intake when they are underweight.     

Cell characteristics and biochemical composition ofDunaliella primolecta Butcher conditioned at different concentrations of dissolved nitrogen

The rates of growth, cell size, elemental and biochemical composition ofDunaliella primolecta were monitored during exponential growth after conditioning over three weeks in media containing different concentrations of nitrogen. The rate of growth, measured both as cell density and cell volume, was correlated positively with the N concentration of the medium (P<0.01). N-starved cells did not grow and died within three days. Cell volume and dry weight per cell were significantly higher (P<0.01) in the N-low (0.45 g-at 1^–1 NO₃-N) condition than in the N-high I condition (3.53 g-at 1^–1 NO₃-N). In the N-high II condition the addition of 1.87 g-at 1^–1 NH₄-N to 3.53 g-at 1^–1 NO₃-N did not significantly enhance growth.The composition was influenced by the availability of nitrogen. The amount of protein per cell decreased significantly from 20.1 to 9.7 pg with reduced nitrate availability between the N-high condition and the N-low condition (P<0.01). The associated carbohydrate content increased significantly from 10.6 to 26.74 pg per cell (P<0.001). These findings confirm the potential for significant variability in the composition ofD. primolecta, both in the natural environment and following experimental manipulation.     

Growth and feeding of juvenile pike <Emphasis Type="Italic">Esox lucius</Emphasis> (Esocidae) of different hatching dates during its first months of life

Groups of fingerlings of the pike Esox lucius, that hatched from the eggs of the same female at the beginning and end of hatching are compared. It was found that larvae of pike of the beginning of hatching passed to external feeding earlier. In the period of mixed and exogenous feeding, they not only grew, but also developed more rapidly than larvae from the same brood. It was shown that pike juveniles of the end of hatching were characterized by a retarded development and growth in the first weeks of life (until reaching a length of 100 mm and a weight of 7 g). In the second month of life, specimens of this group began to feed intensively, grow, and according to body length and weight, reached pike juveniles of the beginning of hatching. Pike fingerlings of the end of hatching were characterized by compensation growth that was manifested at the excess of fish food (at cultivation in separate aquariums when the inhibitory effect of large fish on the growth of small fish was excluded) and in ponds where fish food availability was considerably lower.