Introduced northern pike predation on salmonids in southcentral Alaska

Northern pike (Esox lucius) are opportunistic predators that can switch to alternative prey species after preferred prey have declined. This trophic adaptability allows invasive pike to have negative effects on aquatic food webs. In Southcentral Alaska, invasive pike are a substantial concern because they have spread to important spawning and rearing habitat for salmonids and are hypothesised to be responsible for recent salmonid declines. We described the relative importance of salmonids and other prey species to pike diets in the Deshka River and Alexander Creek in Southcentral Alaska. Salmonids were once abundant in both rivers, but they are now rare in Alexander Creek. In the Deshka River, we found that juvenile Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) dominated pike diets and that small pike consumed more of these salmonids than large pike. In Alexander Creek, pike diets reflected the distribution of spawning salmonids, which decrease with distance upstream. Although salmonids dominated pike diets in the lowest reach of the stream, Arctic lamprey (Lampetra camtschatica) and slimy sculpin (Cottus cognatus) dominated pike diets in the middle and upper reaches. In both rivers, pike density did not influence diet and pike consumed smaller prey items than predicted by their gape‐width. Our data suggest that (1) juvenile salmonids are a dominant prey item for pike, (2) small pike are the primary consumers of juvenile salmonids and (3) pike consume other native fish species when juvenile salmonids are less abundant. Implications of this trophic adaptability are that invasive pike can continue to increase while driving multiple species to low abundance.     

In this issue – March 2011

Wound healing after breech flystrike control methods in lambs · Resistance to synthetic pyrethroids in buffalo flies · Auditory function in older horses · Cutaneous asthenia in a foal · Avian trichomoniasis in an Australian avian practice · Infectious laryngotracheitis in poultry in Australia · Hepatotoxicosis in dogs eating contaminated camel meat · Pulmonary aspergillosis in a cat     

Cabora Bassa Fish Populations Before and During the First Filling Phase

Pre-impoundment surveys were made in 1973-4. The regulatory effect of continual water discharge from Kariba resulted in extensive dry-season aquatic, rooted, vegetal growth and a comparatively high small-fish population. Of a maximum of 38 species found one, Sarotherodon andersoni, was a new Middle Zambezi record. Lotic and shallow-water species were abundant; gill-nets showed moderately high catches per unit effort. In early November 1974 two-month-old Hydrocymis vittatus juveniles were present indicating an abnormal spawning time. Post-impoundment data from closure on 5 December 1974, to mid-August 1975 are given. The dam filled extremely rapidly to within 10 m of retention level but was thereafter drawn down by heavy floodgate discharge, resulting in continuous slow water-flow and the absence of any stratification or explosive plankton reproduction. Small lotic species, previously abundant, immediately disappeared or became scarce. There was a very high survival of new-spawned young of many migratory species. Growth rates, and abnormal feeding habits caused by post-impoundment stresses, of some of these are described. There was relatively poor reproduction of cichlid species. Soon after closure the first year-class predominated over all other age-groups; these juveniles, and small adult species, concentrated under mats of Elchhomia crassipes. One further species new to the area, Haplochromis carlottae, is recorded.     

Relationship between stages of the estrous cycle and bone cell activity in Thoroughbreds

OBJECTIVE: To investigate the relationship between stage of estrous cycle and bone cell activity in Thoroughbreds. SAMPLE POPULATION: Blood samples collected from forty-seven 2-year-old Thoroughbred mares in training for racing. PROCEDURES: Blood samples were collected monthly (in April through September) from the mares. Stage of estrus was determined by assessing serum progesterone concentration. Bone cell activity was determined by measuring concentrations of 2 markers of bone formation (osteocalcin and the carboxy-terminal propeptide of type I collagen [PICP]) and a marker of bone resorption (the cross-linked carboxy-terminal telopeptide of type I collagen [ICTP]) in sera. RESULTS: When the relationship between stage of the estrous cycle and markers of bone cell activity was examined, serum concentrations of both osteocalcin and ICTP were significantly higher in mares that were in the luteal phase, compared with mares that were at other stages of the estrous cycle. Stage of estrus did not affect serum PICP concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that bone cell activity in Thoroughbred mares fluctuates during the estrous cycle; serum concentrations of markers of bone formation and bone resorption are increased during the luteal phase. Further studies are required to determine whether these changes are of clinical importance and increase the risk of injury for mares in training during the breeding season. As in humans, stage of estrus must be considered as a source of uncontrollable variability in serum bone marker concentrations in horses.     

Extrafollicular activation of lymph node B cells by antigen-bearing dendritic cells

In contrast to na?ve T cells that recognize short antigen-derived peptides displayed by specialized antigen-presenting cells, immunoglobulin receptors of B lymphocytes primarily recognize intact proteins. How and where within a lymph node such unprocessed antigens become available for na?ve B cell recognition is not clear. We used two-photon intravital imaging to show that, after exiting high-endothelial venules and before entry into lymph node follicles, B cells survey locally concentrated dendritic cells. Engagement of the B cell receptor by the dendritic cell (DC)-associated antigen leads to lymphocyte calcium signaling, migration arrest, antigen acquisition, and extrafollicular accumulation. These findings suggest a possible role for antigen-specific B-DC interactions in promoting T cell-dependent antibody responses in vivo.     

Evaluation of three different histamine concentrations in intradermal testing of normal cats and attempted determination of 'irritant' threshold concentrations for 48 allergens

The purpose of this study was to determine the optimal histamine concentration and 'irritant' allergen threshold concentrations in intradermal testing (IDT) in normal cats. Thirty healthy cats were tested with three different histamine concentrations and four different concentrations of each allergen. The optimal histamine concentration was determined to be 1: 50,000 w/v (0.05 mg mL(-1)). Using this histamine concentration, the 'irritant' threshold concentration for most allergens was above the highest concentrations tested (4,000 PNU mL(-1) for 41 allergens and 700 PNU mL(-1) for human dander). The 'irritant' threshold concentration for flea antigen was determined to be 1:750 w/v. More than 10% of the tested cats showed positive reactions to Dermatophagoides farinae, Dermatophagoides pteronyssinus, housefly, mosquito and moth at every allergen concentration, which suggests that the 'irritant' threshold concentration for these allergens is below 1,000 PNU mL(-1), the lowest allergen concentration tested. Our results confirm previous studies in indicating that allergen and histamine concentrations used in feline IDT may need to be revised.     

Fetal protection following exposure to calves persistently infected with bovine viral diarrhea virus type 2 sixteen months after primary vaccination of the dams

This study demonstrated that the bovine viral diarrhea virus (BVDV; types 1 and 2) fractions of a multivalent vaccine protected pregnant heifers and their fetuses at 149 to 217 days of gestation against exposure to calves persistently infected with BVDV type 2a. Eighty percent (eight of 10) of the control heifers were viremic at least 1 day following challenge, whereas all (20 of 20) BVDV-vaccinated heifers were virus isolation-negative on all postchallenge assessment days. Ninety percent (nine of 10) of the calves born to control heifers but only 5% (one of 20) of calves born to BVDV-vaccinated heifers seroconverted to BVDV type 2 before ingesting colostrum. One calf born to a control heifer was persistently infected. No calves from BVDV-vaccinated heifers were persistently infected.