Period Of High Mortality Research Articles

Weights, Breeding, and Survival in European Sparrowhawks

Abstract No significant diurnal variation in mean weight was detected in trapped European Sparrowhawks (Accipiter nisus). Weights of males fluctuated rather little through the year, but were highest in March and lowest in August. During the breeding cycle, males lost weight slightly in the prelay/early laying periods, when they were feeding females in preparation for egg production, and in the late nestling/postfledging periods, when they were feeding large young. Weights of females fluctuated greatly during the year: they were highest in May at the time of egg laying and lowest in August at the end of breeding. Females increased in weight by 40-50 g (15%) in the 10-20 days before laying; lost about 20 g over the laying period, on average; maintained high weight through much of incubation; and lost weight during the nestling period. The main functions of the extra body reserve are probably to buffer the female against temporary food shortages during incubation and to enable her to feed the chicks preferentially in the nestling period. Females that did not lay eggs remained low in weight throughout the early part of the breeding season and were then significantly lighter than breeders. Moreover, females that laid large clutches were heavier throughout the prelaying and laying periods than were females that laid small clutches, and females that subsequently hatched their eggs started incubation at a significantly greater weight than did those that deserted their eggs. We suggest that clutch size and breeding success are dependent on the female being able to maintain high weight during the periods she is dependent on the male for food and, hence, on the hunting success of the male. First-year birds of both sexes weighed less than adults throughout the year and were especially light during their first 2 months of independent life. This was probably a period of high mortality, especially in males, in which a clear relationship emerged between weight and survival prospects.

Causes of High Mortality among Cultured Larval Walleyes

After 40 years of research in North America, the problem of variable and low survival of young walleyes Stizostedion vitreum during rearing remains unresolved. In laboratory experiments, a period of high mortality was identified when postlarvae shifted from endogenous to exogenous feeding. The main factors that influenced mortality were food density, the timing of food availability, fish density, and culture volume. Larvae at different developmental stages showed different responses to these factors. Cannibalism within a cohort caused significant mortality during the postlarval stage. An optimum food density of 100 daphnids per liter, a larval density of less than 1 fish per liter, a minimum culture volume of 20 liters, and immediate food availability when larvae first feed are suggested to increase survival of postlarvae.

Factors Associated with the Seasonal Variation in the Incidence of Pituitary Cysts in Nine-Spined Sticklebacks,Pungitius pungitiusL.

Cysts among the prolactin cells in the pituitary gland of the nine-spined stickleback, Pungitius pungitius L., are most common during and shortly after periods of high mortality that mark the end of the reproductive season. Fish are oldest at this time of year. Nevertheless, cysts may occur in breeding as well as spent fish, and their presence does not relate to changes in oocyte development. They can be induced by starving animals in February, but not in September—October. Starved fish always have small prolactin cells and nuclei. It is suggested that cysts form in older fish in response to stress, be this natural or induced. No correlation was noticed between the condition factor of fish caught in the wild, and the incidence of pituitary cysts.

Relationships between effects of environmental temperature and seston on growth and mortality of Mytilus edulis in a temperate northern estuary

The growth and mortality of experimentally-rafted Mytilus edulis L. of known age at 7 locations in a northern estuary (Damariscotta River, Maine, USA) were related to environmental temperatures and to the presence or absence of various potential food sources. All particles were regarded as potential food substrates. Growth decreased appreciably at sites where water temperatures exceeded 20°C, but mussels survived a wide range of elevated temperature exposures, ranging from 0 to 149 degree-days in excess of 20°C. The maximum temperature was 25°C. Mortalities of mussels at all sites but did affect the extent of mortality, which increased abruptly in late summer, when water temperatures were declining. Differences in degree-days of exposure to elevated temperatures did not influence the timing of mortality, which occurred synchronously at all times, but did affect the extent of mortality, which ranged from 35 to 90%. The period of high mortality was preceded by a rapid decline in phytoplankton standing crop. Total particle concentrations decreased during this period, but the shift toward larger particles suggests that there was little, if any, decrease in total volume of material in the seston, at least through August. It is suggested that living phytoplankton provided the critical energy source for these mussels, and that the mortalities were caused by rapidly reduced ration at a time of metabolic stress. The role of temperature and the possible role of the gametogenic cycle are discussed. In addition, the feeding efficiency of M. edulis may have decreased during this period due to an increase in mean particle diameter. Chlorophyll was divided into a nannoplankton fraction ( 20 μm). A smaller size criterion for this distinction is proposed for future studies. The importance of nannoplankton to the primary production of this estuary and the role of nannoplankton and nannoplankton-sized particles in the diet of mussels in nature are discussed.

Comparative acute oral toxicity of sodium warfarin and microcrystalline warfarin in the Sprague-Dawley rat

Summary The acute oral toxicities of sodium warfarin and a microcrystalline form of acid (enol) warfarin (MICROFARIN) were compared in male and female Sprague-Dawley rats. The drugs were administered in carboxymethylcellulose by gastric needle, and the rats were observed for a 14-day period. The LD 50 , calculated on the basis of probit-log plots and formulae, according to Bliss, for sodium warfarin was 100.3 ± 1.5 mg/kg (0.3037 mmol/kg) for male rats and 8.7 ± 1.2 mg/kg (0.0263 mmol/kg) for female rats. The LD 50 for microcrystalline warfarin for male rats was 112 ± 1.6 mg/kg (0.363 mmol/kg) and 10.4 ± 1.1 mg/kg (0.00337 mmol/kg) for female rats. Both warfarin preparations exhibited the same range of toxicity; the toxicity for both drugs was approximately 10 times greater in the female than in the male rat. Except for the highest dose of warfarin preparations studied (320 mg/kg), the period of highest mortality was between the 4th and 10th post-treatment day. Autopsy revealed hemorrhages into the intestine, thoracic cavity, peritoneal cavity, and urinary bladder. The data show that the microcrystalline form of warfarin is absorbed from the gastrointestinal tract and that its LD 50 is similar to that of sodium warfarin.

Diphtheria Infection and Morbidity in Cleveland, 1937-1939

FOLLOWING a period of high mortality, unprecedented in the statistical record and exceeding 300 per 100,000 in 1877, the decline of diphtheria in Cleveland was heralded by a precipitate fall in the death rate in 1879. After 5 years at a level of about 180, a gradual decline commenced, which continued, with some interruptions, to 1909, when the rate was 12.4. In the succeeding 18 years, with the exception of 1924, higher rates were experienced. Then, after 1927, the decline was resumed and greatly accelerated. Since 1930 mortality has been at a very low level. In 1938 the rate was only 0.5, a reduction of 97 per cent from that of 1927. The number of cases reported in each year, since 1910, has varied directly with the number of deaths. Thus there has been no evidence of decreasing severity of the disease. The case fatality was 7.6 per cent for the period 1910-1914; 7.9 for 1915-1919; 8.2 for 1920-1924; 7.2 for 1925-1929; 7.0 for 1930-1934, and 8.5 for 1935-1938.

MORTALITY OF THE COD EGG IN RELATION TO TEMPERATURE

1. Experiments were carried out at four different temperatures in the supra-optimal range of development for the cod egg.2. Development from the two-cell stage to 50 per cent hatched required 8.5 days at 12° C., 9 days at 10° C., 11.5 days at 8° C., and 17.2 days at 6° C.3. At all temperatures an initial period of high mortality decreased with the closing of the blastopore and was followed by a period of low mortality until the embryo was three-quarters the circumference of the egg membranes, when the mortality steadily increased up to hatching.4. The hatching period is discussed with reference to its use as a stage of development.

RECENT PHASES OF THORACIC SURGERY

The development of the surgery of the thorax has been slower than that of any other field. Although operations for drainage in cases of empyema were carried out by the ancients, it is only in very modern times that any extensive surgical procedures have been undertaken within the thorax. The newness and the present undeveloped state of the surgery of this region are reflected not only in the high mortality of some of the procedures, but also in the lack of any sort of uniform agreement as to what constitute operative indications in many of the conditions. Thoracic surgery is now passing through the period of high mortality and indifferent results which characterized the field of abdominal surgery twenty-five years ago, and of the surgery of the brain even more recently. In the future it will unquestionably be made safer by a better understanding of the physiology and pathology involved,