Diel variation in egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea : Branchiura)

Removal of deposited eggs could be a useful control strategy for the damaging fish ectoparasite Argulus foliaceus, but focused control requires knowledge of egg-laying patterns. Here, we investigated diel changes in the egg-laying behaviour of a natural population of A. foliaceus. Data were collected from 17-28 May 2004. Days were divided into 3 time periods: 06:00-14:00, 14:00-22:00 and 22:00-06:00 h. Significantly more egg clutches were laid from 06:00-14:00 h than during the other 2 time periods, which were not significantly different from each other. Significantly more egg clutches per hour were laid during hours of daylight as compared to hours of darkness. Significantly more egg clutches were laid in the top 1 m of the water column than at the bottom, and this was consistent throughout all 3 time periods. It is suggested that the increase in egg-laying activity during daylight hours may be due to a higher motivation to search for hosts during the night and an increased ability to locate silhouetted egg-laying sites during the day. These data can provide information useful for egg removal and control strategies.

Seasonal and vertical patterns of egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea : Branchiura)

Argulus foliaceus is a damaging fish ectoparasite for which new control measures are being developed based on egg-removal, In an attempt to develop further understanding of seasonal and vertical egg-laying patterns in this parasite, egg-laying activity was monitored over the period 14 April to 17 November 2003 in 2 rainbow trout Oncorhynchus mykiss fisheries in Northern Ireland, UK. At Site 1, egg-laying was continuous from 21 April to 17 November, when water temperature was above 8 to 10 degrees C. At Site 2, egg-laying was continuous from 4 June to 29 October. In the early months of the season, egg-laying was recorded mainly within the top 1 m of the water column; however, a significant shift to deep water egg-laying was recorded between 7 July and 17 November at Site 1 and between 20 August and 29 October at Site 2. Egg clutches were preferentially laid at depths of up to 8.5 m during this time (Site 2), a feature of egg-laying hitherto unappreciated. Temperature and dissolved oxygen did not differ significantly among depths, but there was an increase in water clarity over time. However, the precise environmental triggers for deep water egg-laying are still unclear. These new insights into the reproductive behaviour of this species will be useful in developing control methods based on egg-removal.

Development of an ELISA screening test for nitroimidazoles in egg and chicken muscle

An antibody was generated that can bind metronidazole (MNZ), a nitroimidazole drug used in veterinary medicine to treat poultry for coccidiosis and histomoniasis. A direct competitive enzyme-linked immunosorbent assay (cELISA) is described. It was used to characterise binding of this antibody to a number of nitroimidazole drugs. It displayed cross-reactivity with dimetridazole (DMZ), ronidazole (RNZ), hydroxydimetridazole (DMZOH), and ipronidazole (IPZ).

Screening for the coccidiostats halofuginone and nicarbazin in egg and chicken muscle: development of an ELISA

Nicarbazin and halofuginone have been widely used as coccidiostats for the prevention and treatment of coccidiosis in poultry. It has been shown that accidental cross-contamination of feed can lead to residues of these compounds in eggs and/or muscle. This paper describes a direct competitive assay for detecting halofuginone and nicarbazin, developed as qualitative screening assay. In an optimized competitive ELISA, antibodies showed 50% binding inhibition at approximately 0.08 ng ml(-1) for halofuginone and 2.5 ng ml(-1) for dinitrocarbanilide (marker residue for nicarbazin). Extraction from the matrix was carried out with acetonitrile followed by a wash with hexane. The assay's detection capability (CCbeta) for halofuginone was

The `Chicken and Egg' of Subjective and Social Factors in Desistance from Crime

It is now widely acknowledged that progression from persistent offending to desistance from crime is the outcome of a complex interaction between subjective/ agency factors and social/environmental factors. A methodological challenge for desistance researchers is to unravel the differential impacts of these internal and external factors and the sequence in which they come into play. Towards this, the present investigation draws on a prospective study of 130 male property offenders, interviewed in the 1990s (the Oxford Recidivism Study), and followed up 10 years later. The analysis supports a `subjective—social model' in which subjective states measured before release have a direct effect on recidivism as well as indirect effects through their impact on social circumstances experienced after release from prison.

Fasciola hepatica: Histology of the testis in egg-producing adults of several laboratory-maintained isolates of flukes grown to maturity in cattle and sheep and in flukes from naturally infected hosts

A total of 8 calves approximately 6 months old and 22 lambs of similar age were infected with metacercariae of Fasciola hepatica of various laboratory-maintained isolates including: Cullompton (sensitive to triclabendazole) and Sligo, Oberon and Leon (reported as resistant to triclabendazole). Ten to 16 weeks after infection, flukes were harvested from these experimental animals and the histology of the testis tissue was examined in a representative sample of flukes from each population. Adult wild-type flukes were also collected from 5 chronically infected cattle and 7 chronically infected sheep identified at post-mortem inspection. The testis tissue of these flukes was compared with that of the various laboratory-maintained isolates. Whilst the testes of the wild-type, Oberon and Leon flukes displayed all the usual cell types associated with spermatogenesis in Fasciola hepatica (spermatogonia, spermatocytes, spermatids and mature sperm), the Cullompton flukes from both cattle and sheep showed arrested spermatogenesis, with no stages later than primary spermatocytes represented in the testis profiles. The presence of numerous eosinophilic apoptotic bodies and nuclear fragments suggested that meiotic division was anomalous and incomplete. In contrast to the wild-type flukes, no mature spermatozoa were present in the testes or amongst the shelled eggs in the uterus. A high proportion of the eggs collected from these flukes hatched to release normal-appearing miracidia after an appropriate incubation period, as indeed was the case with all isolates examined and the wild-type flukes. It is concluded that the eggs of Cullompton flukes are capable of development without fertilization, i.e. are parthenogenetic. The implications of this for rapid evolution of resistant clones following an anthelmintic selection event are discussed. Amongst the Sligo flukes examined, two subtypes were recognised, namely, those flukes with all stages of spermatogenesis and mature spermatozoa present in the testes (type 1), and those flukes with all stages of spermatogenesis up to spermatids present, but no maturing spermatozoa in the testes (type 2). Each sheep infected with the Sligo isolate had both type 1 (approximately 60%) and type 2 (approximately 40%) flukes present in the population. Spermatozoa were found amongst the eggs in the uterus in 64% of flukes and this did not necessarily reflect the occurrence of spermatozoa in the testis profiles of particular flukes, suggesting that cross-fertilization had occurred. The apparent disruption of meiosis in the spermatocytes of the Cullompton flukes is consistent with reports that Cullompton flukes are triploid (3n = 30), whereas the Sligo and wild-type flukes are diploid (2n = 20). In the Sligo flukes the populations are apparently genetically heterogenous, with a proportion of the flukes unable to produce fully formed spermatozoa perhaps because of a failure in spermiogenesis involving elongation of the nucleus during morphogenesis. (C) 2008 Elsevier B.V. All rights reserved.