A histological evaluation of pansteatitis-affected Mozambique tilapia,Oreochromis mossambicus (Peters 1852), from different geographical locations in South Africa

Pansteatitis is the leading cause for the decline in Nile crocodile populations and the sporadic mortality of fish in the Olifants River System, South Africa. To determine the prevalence of this disease in lentic systems, Mozambique tilapia, Oreochromis mossambicus, were collected from Lake Loskop, Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi. The former three impoundments are located within the main stem of the Olifants River, while the latter, which is geographically isolated and situated in the Limpopo River System, served as a reference site. Mesenteric adipose, liver, serosa of the swim bladder, gill and the skeletal muscle of fish sampled were examined for gross and microscopic evidence of pansteatitis. Microscopically observed changes were used to statistically compare pansteatitis prevalence between samples and sites. Based on histopathological evaluation, the adipose tissue in the liver, swim bladder serosa and coelom from severely debilitated individuals showed the most significant pathological changes. Lesions indicative of steatitis were observed in fish collected from Lake Loskop (75%), Lake Flag Boshielo (22%) and Lake Luphephe-Nwanedi (15%). Further investigation is warranted to understand the pervasiveness and mechanisms driving pathological changes of pansteatitis at Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi.     

Pansteatitis in polluted Olifants River impoundments: nutritional perspectives on fish in a eutrophic lake,Lake Loskop,South Africa

This study compares the aetiology of pansteatitis in Lake Loskop, relative to two other impoundments along the Olifants River. Macroscopic and microscopic pathology, age determination and analysis of stomach content, fatty acids and stable isotopes explain the high prevalence of pansteatitis in Oreochromis mossambicus (Peters) and several other species in Lake Loskop. All the dietary indicator comparisons between pansteatitis‐affected and healthy fish fail to support a systemic cause. Pansteatitis in Lake Loskop was linked to size and weight of O. mossambicus, but not to ontogenic age. Fish in Lake Loskop showed abnormally high omega‐3 to omega‐6 fatty acid ratios normally only found in marine fish with no significant difference in degree of assimilation of these fatty acids between pansteatitis‐affected and healthy fish. This explains the vulnerability to, but not the occurrence of, pansteatitis. As a cause for the pansteatitis, these results point towards sporadic vitamin E‐depleting trigger events, known sporadic fish die‐off occurrences that provide surviving fish with a rich source of rancid fats on which to scavenge. The mechanism ties pansteatitis to eutrophication and trophic cascade effects, the intrinsic drivers of the disease and suggests an adaptive management strategy that might be applied by relevant conservation authorities.     

QTL controlling partial resistance to Stagonospora nodorum leaf blotch in winter wheat cultivar Alba

Stagonospora nodorum blotch (SNB) is an important foliar and glume disease in cereals. Inheritance of SNB resistance in wheat appears quantitative. The development of partially resistant cultivars seems to be the only effective way to combat the pathogen. Partial resistance components like length of incubation period (INC), disease severity (DIS) and length of latent period (LAT) were evaluated on a population of doubled-haploids derived from a cross between the partially resistant cultivar Alba and the susceptible cultivar Begra. Experiments were conducted in controlled environments and the fifth leaf was examined. Molecular analyses were based on bulked segregant analyses (BSA) and screening with 240 microsatellites DNA markers. The QTL analysis revealed QTL on chromosome 6AL (designated as QSnl.ihar-6A) and putative QTL on chromosome 6D. The QSnl.ihar-6A accounted for 36% of the phenotypic variance for DIS and 14% for INC. The putative QTL accounted for 10% of the variability in INC and 8% of DIS components of SNB resistance.     

Sodium and chloride distribution in salt-stressed Prunus salicina, a deciduous tree species

Measurements were made over four growing seasons of the Na(+) and Cl(-) content of leaves and woody tissues (twigs, branches, trunk and roots) of mature, fruit-bearing Prunus salicina Lindl. (on Marianna 2624 rootstock) trees irrigated during the growing season with water containing 3, 14 or 28 mM salt (2/1 molar ratio of NaCl and CaCl(2)). At the beginning of the study, the trees were 19 years old. Woody tissues of trees irrigated with water containing 14 or 28 mM salt accumulated Na(+) and Cl(-). Leaves of trees irrigated with water containing 14 or 28 mM salt accumulated Cl(-), but not Na(+), unless they had visible symptoms of salt injury. X-Ray microanalysis of leaf mesophyll cells indicated some ability of the cells to sequester Cl(-) in the vacuole. The data demonstrate a capacity for ion compartmentation among tissues and cell organelles in mature Prunus salicina, which may explain the ability of the species to survive low levels of salinity for several years in the field.     

Reclamation of saline organic soil

Summary Reclamation of saline, organic soils in the Sacramento-San Joaquin Delta of California was accomplished by both sprinkling and continuously ponding water on the soil surface. The reclamation data support the generalized guideline established for saline, organic soil.A 70% reduction in the average root zone salinity required 3 months under ponding, compared to 4 months under sprinkling. Although accurate measures of water application on the ponded trials were not possible, the limited data indicate that the amount of water required is about the same per unit depth of soil reclaimed for both ponding and sprinkling. Reclamation proceeded more quickly under the second ponding trial than for sprinkling or the first ponding trial because of improved subsurface drainage. With sprinklers, 70% of the salt was removed from the soil profile to a depth of 1.2 m after 850 mm of leaching water entered the profile. Reclamation by ponding required about the same quantity of water but the water required for leaching could be reduced significantly by improved drainage.     

Using a GnRH agonist to obtain an index of testosterone secretory capacity in the cockatiel (Nymphicus hollandicus) and sulphur-crested cockatoo (Cacatua galerita)

Objective   Validation of a stimulation test for determining the steroidogenic capacity of the parrot testis. The major aim was to characterise testosterone secretion after injection of a gonadotropin-releasing hormone agonist (GnRHa), then use the test to investigate seasonal reproduction in the male cockatiel.
Procedure   A synthetic GnRHa (buserelin; 8.0 µg of peptide/kg bodyweight) was injected IM into male cockatiels (n = 7) and sulphur-crested cockatoos (n = 3) and serial blood samples collected at 0, 30, 60, 90 and 120 min after administration. Once validated, the technique was subsequently used to examine seasonal changes (23 months) in the testosterone profile of a captive cockatiel population.
Results   Injection of buserelin resulted in a significant increase in the testosterone concentration of cockatiel plasma, with maximal concentrations occurring at approximately 60 (1.33 ± 0.08 ng/mL) to 90 min (1.22 ± 0.08 ng/mL) after injection. Although no clear pattern of seasonal variation in testosterone secretion was detected in cockatiel plasma, samples taken 60 and 90 min after administration showed a significant increase in all seasons. Injection of buserelin in the sulphur-crested cockatoo also resulted in increased testosterone secretion, with maximal concentrations obtained after 90 min.
Conclusion   Buserelin can be used to obtain a reliable index of the prevailing testosterone capacity of the cockatiel and cockatoo testis. With further studies, this test may be incorporated into clinical assessment of reproductive status.     

A method for estimating fish density through the catches of gillnets

We propose a new method for estimating fish density using catches obtained by gillnets of given mesh size. This method builds on work for estimating the number of fish approaching a gillnet by modelling the fish movement that leads to a gillnet encounter. The theoretical framework is developed, and the method is tested on catch data for cod Gadus morhua and Dolly Varden Salvelinus malma to demonstrate how the method can be applied. The method relies on knowledge of geometric properties of the net, and morphological and behavioural properties of the fish, so we explore the sensitivity of the estimates to some of these parameters. Estimates are most sensitive to the morphological parameter of the angle the mouth is open while swimming and largely invariant to estimates of uncertain parameters like maximum number of fish that can be caught by the particular net.