Regulation of Gonadotropin-Releasing Hormone (GnRH)-Receptor Gene Expression in Tilapia: Effect of GnRH and Dopamine

The present work was designed to study certain aspects of the endocrine regulation of gonadotropin-releasing hormone receptor (GnRH-R) in the pituitary of the teleost fish tilapia. A GnRH-R was cloned from the pituitary of hybrid tilapia (taGnRH-R) and was identified as a typical seven-transmembrane receptor. Northern blot analysis revealed a single GnRH-R transcript in the pituitary of approximately 2.3 kilobases. The taGnRH-R mRNA levels were significantly higher in females than in males. Injection of the salmon GnRH analog (sGnRHa; 5–50 μg/kg) increased the steady-state levels of taGnRH-R mRNA, with the highest response recorded at 25 μg/kg and at 36 h. At the higher dose of sGnRHa (50 μg/kg), taGnRH-R transcript appeared to be down-regulated. Exposure of tilapia pituitary cells in culture to graded doses (0.1–100 nM) of seabream (sbGnRH = GnRH I), chicken II (cGnRH II), or salmon GnRH (sGnRH = GnRH III) resulted in a significant increase in taGnRH-R mRNA levels. The highest levels of both LH release and taGnRH-R mRNA levels were recorded after exposure to cGnRH II and the lowest after exposure to sbGnRH. The dopamine-agonist quinpirole suppressed LH release and mRNA levels of taGnRH-R, indicating an inhibitory effect on GnRH-R synthesis. Collectively, these data provide evidence that GnRH in tilapia can up- regulate, whereas dopamine down-regulates, taGnRH-R mRNA levels.

Pheromone-trapping of Carpophilus spp. (Coleoptera: Nitidulidae) in stone fruit orchards near Gosford, New South Wales: Fauna, seasonality and effect of insecticides

Traps baited with synthetic aggregation pheromones of Carpophilus hemipterus (L.), Carpophilus mutilatus Erichson and Carpophilus davidsoni Dobson and fermenting bread dough were used to identify the fauna and monitor the seasonal abundance of Carpophilus spp. in insecticide treated peach and nectarine orchards in the Gosford area of coastal New South Wales. In four orchards 67 178 beetles were trapped during 1994–1995, with C. davidsoni (82%) and Carpophilus gaveni (Dobson) (12.2%) dominating catches. Five species (C. hemipterus, C. mutilatus, Carpophilus marginellus Motschulsky, Carpophilus humeralis (F.) and an unidentified species) each accounted for 0.2–3.2% of trapped beetles. Carpophilus davidsoni was most abundant during late September–early October but numbers declined rapidly during October, usually before insecticides were applied. Spring populations of Carpophilus spp. were very large in 1994–1995 (1843–2588 per trap per week). However, despite a preharvest population decline of approximately 95% and 2–11 applications of insecticide, 14–545 beetles per trap per week (above the arbitrary fruit damage threshold of 10 beetles per trap per week) were recorded during the harvest period and fruit damage occurred at three of the four orchards. Lower preharvest populations in 1995–1996 (< 600 per trap per week) and up to six applications of insecticide resulted in < 10 beetles per trap per week during most of the harvest period and minimal or no fruit damage. The implications of these results for the integrated management of Carpophilus spp. in coastal and inland areas of southeastern Australia are discussed.

Impact of cold storage on glucosinolate levels in seed-sprouts of broccoli, rocket, white radish and kohl-rabi

The effect of cold storage on glucosinolate concentration was examined in 7-day-old seed-sprouts of broccoli, kohl rabi, white radish and rocket. Principal glucosinolates identified were glucoraphanin and glucoerucin (in broccoli, kohl rabi and rocket), glucoiberin (in broccoli and kohl rabi), and glucoraphenin and glucodehydroerucin (in white radish). Generally, sprouts showed no significant changes in individual glucosinolate concentrations during storage at 4°C for 3 weeks. The exception to this was rocket, which showed a significant decline in glucoerucin and glucoraphanin after 1 and 2 weeks, respectively. These preliminary results indicate that as there is no significant loss of glucosinolates in broccoli, radish and kohl rabi sprouts, these sprouts may be stored under domestic refrigeration conditions without significant loss of potential anti-cancer compounds. Rocket sprouts, on the other hand, should be consumed soon after purchase if glucosinolate levels are to be maintained.

Modelling discard ogives from Irish demersal fisheries

Annual discard ogives were estimated using generalized additive models (GAMs) for four demersal fish species: whiting, haddock, megrim, and plaice. The analysis was based on data collected on board commercial vessels and at Irish fishing ports from 1995 to 2003. For all species the most important factors influencing annual discard ogives were fleet (combination of gear, fishing ground, and targeted species), mean length of the catch and year, and, for megrim, also minimum landing size. The length at which fish are discarded has increased since 2000 for haddock, whiting, and plaice. In contrast, discarded length has decreased for megrim, accompanying a reduction in minimum landing size in 2000.

Variable growth rates of the tropical estuarine fish barramundi Lates calcarifer (Bloch) under different freshwater flow conditions

Relationships between freshwater flows and growth rates of the opportunistic predatory finfish barramundi Lates calcarifer in a dry tropical estuary were examined using data from a long-term tag-recapture programme. Lagged effects were not investigated. After accounting for length at release, time at liberty and seasonal variation (e.g. winter, spring, summer and autumn), growth rates were significantly and positively related to fresh water flowing to the estuary. Effects were present at relatively low levels of freshwater flow (i.e. 2.15 m3 s-1, the 5th percentile of the mean flow rate experienced by fish in the study during time at liberty). The analysis, although correlative, provides quantitative evidence to support the hypothesis that freshwater flows are important in driving the productivity of estuaries and can improve growth of species high in the trophic chain.

How effective are broad-scale nutrient mass balances for determining the sustainability of lot-feed manure application?

Nutrient mass balances have been used to assess a variety of land resource scenarios, at various scales. They are widely used as a simple basis for policy, planning, and regulatory decisions but it is not clear how accurately they reflect reality. This study provides a critique of broad-scale nutrient mass balances, with particular application to the fertiliser use of beef lot-feeding manure in Queensland. Mass balances completed at the district and farm scale were found to misrepresent actual manure management behaviour and potentially the risk of nutrient contamination of water resources. The difficulties of handling stockpile manure and concerns about soil compaction mean that manure is spread thickly over a few paddocks at a time and not evenly across a whole farm. Consequently, higher nutrient loads were applied to a single paddock less frequently than annually. This resulted in years with excess nitrogen, phosphorus, and potassium remaining in the soil profile. This conclusion was supported by evidence of significant nutrient movement in several of the soil profiles studied. Spreading manure is profitable, but maximum returns can be associated with increased risk of nutrient leaching relative to conventional inorganic fertiliser practices. Bio-economic simulations found this increased risk where manure was applied to supply crop nitrogen requirements (the practice of the case study farms, 200-5000 head lot-feeders). Thus, the use of broad-scale mass balances can be misleading because paddock management is spatially heterogeneous and this leads to increased local potential for nutrient loss. In response to the effect of spatial heterogeneity policy makers who intend to use mass balance techniques to estimate potential for nutrient contamination should apply these techniques conservatively.

Diet quality and liveweight gain of steers grazing Leucaena-grass pasture estimated with faecal near infrared reflectance spectroscopy (F.NIRS)

Three drafts of Bos indicus cross steers (initially 178-216 kg) grazed Leucaena-grass pasture [Leucaena leucocephala subspecies glabrata cv. Cunningham with green panic (Panicum maximum cv. trichoglume)] from late winter through to autumn during three consecutive years in the Burnett region of south-east Queensland. Measured daily weight gain (DWGActual) of the steers was generally 0.7-1.1 kg/day during the summer months. Estimated intakes of metabolisable energy and dry matter (DM) were calculated from feeding standards as the intakes required by the steers to grow at the DWGActual. Diet attributes were predicted from near infrared reflectance spectroscopy spectra of faeces (F.NIRS) using established calibration equations appropriate for northern Australian forages. Inclusion of some additional reference samples from cattle consuming Leucaena diets into F.NIRS calibrations based on grass and herbaceous legume-grass pastures improved prediction of the proportion of Leucaena in the diet. Mahalanobis distance values supported the hypothesis that the F.NIRS predictions of diet crude protein concentration and DM digestibility (DMD) were acceptable. F.NIRS indicated that the percentage of Leucaena in the diet varied widely (10-99%). Diet crude protein concentration and DMD were usually high, averaging 12.4 and 62%, respectively, and were related asymptotically to the percentage of Leucaena in the diet (R2 = 0.48 and 0.33, respectively). F.NIRS calibrations for DWG were not satisfactory to predict this variable from an individual faecal sample since the s.e. of prediction were 0.33-0.40 kg/day. Cumulative steer liveweight (LW) predicted from F.NIRS DWG calibrations, which had been previously developed with tropical grass and grass-herbaceous legume pastures, greatly overestimated the measured steer LW; therefore, these calibrations were not useful. Cumulative steer LW predicted from a modified F.NIRS DWG calibration, which included data from the present study, was strongly correlated (R2 = 0.95) with steer LW but overestimated LW by 19-31 kg after 8 months. Additional reference data are needed to develop robust F.NIRS calibrations to encompass the diversity of Leucaena pastures of northern Australia. In conclusion, the experiment demonstrated that F.NIRS could improve understanding of diet quality and nutrient intake of cattle grazing Leucaena-grass pasture, and the relationships between nutrient supply and cattle growth.

Mycotoxins and toxigenic fungi in sago starch from Papua New Guinea

Aims: To assay sago starch from Papua New Guinea (PNG) for important mycotoxins and to test fungal isolates from sago for mycotoxin production in culture. Methods and Results: Sago starch collected from Western and East Sepik Provinces was assayed for aflatoxins, ochratoxin A, cyclopiazonic acid, sterigmatocystin, citrinin and zearalenone and all 51 samples were negative. Frequently isolated species of Penicillium (13), Aspergillus (five) and Fusarium (one) were cultured on wheat grain, and tested for the production of ochratoxin A, cyclopiazonic acid, sterigmatocystin, citrinin, patulin and penicillic acid. All 12 isolates of P. citrinin and one of two A. flavipes isolates produced citrinin. A single isolate of A. versicolor produced sterigmatocystin. No other mycotoxins were detected in these cultures. Conclusions: No evidence was found of systemic mycotoxin contamination of sago starch. However, the isolation of several mycotoxigenic fungi shows the potential for citrinin and other mycotoxins to be produced in sago stored under special conditions. Significance and Impact of the study: Sago starch is the staple carbohydrate in lowland PNG and the absence of mycotoxins in freshly prepared sago starch is a positive finding. However, the frequent isolation of citrinin-producing fungi indicates a potential health risk for sago consumers, and food safety is dependant on promoting good storage practices.

Effect of DNA extraction on ageing success in coral trout (Plectropomus leopardus) otoliths

To maximize the information commonly collected from otoliths, the effect of DNA extraction on the estimation of age with otoliths was evaluated by comparing sagittal otolith samples from common coral trout (Plectropomus leopardus) for clarity and ageing discrepancies in DNA-extracted and untreated control otoliths. The DNA extraction process had no significant effect, indicating that archived otoliths can be used as a source of DNA while retaining their utility for age estimation.

Population structure, effective population size and adverse effects of stocking in the endangered Australian eastern freshwater cod Maccullochella ikei

Microsatellite markers were used to examine spatio-temporal genetic variation in the endangered eastern freshwater cod Maccullochella ikei in the Clarence River system, eastern Australia. High levels of population structure were detected. A model-based clustering analysis of multilocus genotypes identified four populations that were highly differentiated by F-statistics (FST = 0· 09 − 0· 49; P < 0· 05), suggesting fragmentation and restricted dispersal particularly among upstream sites. Hatchery breeding programmes were used to re-establish locally extirpated populations and to supplement remnant populations. Bayesian and frequency-based analyses of hatchery fingerling samples provided evidence for population admixture in the hatchery, with the majority of parental stock sourced from distinct upstream sites. Comparison between historical and contemporary wild-caught samples showed a significant loss of heterozygosity (21%) and allelic richness (24%) in the Mann and Nymboida Rivers since the commencement of stocking. Fragmentation may have been a causative factor; however, temporal shifts in allele frequencies suggest swamping with hatchery-produced M. ikei has contributed to the genetic decline in the largest wild population. This study demonstrates the importance of using information on genetic variation and population structure in the management of breeding and stocking programmes, particularly for threatened species.

Coordinator's report: rules for nomenclature and gene symbolization in barley.

In this volume, the recommended rules for nomenclature and gene symbolization in barley are reprinted. The current lists of new and revised barley genetic stock descriptions are presented by BGS number order and by locus symbol in alphabetical order.

Reproductive strategies of two invasive tilapia species Oreochromis mossambicus and Tilapia mariae in northern Australia

The reproductive biology of two invasive tilapia species, Oreochromis mossambicus and Tilapia mariae, resident in freshwater habitats in north-eastern Australia was investigated. Oreochromis mossambicus exhibited plasticity in some of its life-history characteristics that enhanced its ability to occupy a range of habitats. These included a shallow, weed-choked, freshwater coastal drain that was subject to temperature and dissolved oxygen extremes and water-level fluctuations to cooler, relatively high-altitude impoundments. Adaptations to harsher conditions included a decreased total length (LT) and age ( A) at 50% maturity (m50), short somatic growth intervals, early maturation and higher relative fecundities. Potential fecundity in both species was relatively low, but parental care ensured high survival rates of both eggs and larvae. No significant difference in the relative fecundity of T. mariae populations in a large impoundment and a coastal river was found, but there were significant differences in relative fecundities between several of the O. mossambicus populations sampled. Total length ( LT) and age at 50% maturity of O. mossambicus populations varied considerably depending on habitat. The LTm50 and Am50 values for male and female O. mossambicus in a large impoundment were considerably greater than for those resident in a small coastal drain. Monthly gonad developmental stages and gonado-somatic indices suggested that in coastal areas, spawning of O. mossambicus and T. mariae occurred throughout most of the year while in cooler, high-altitude impoundments, spawning peaked in the warmer, summer months. The contribution these reproductive characteristics make to the success of both species as colonizers is discussed in the context of future control and management options for tilapia incursions in Australia.

Comparison of the reproductive ecology of two sympatric blacktip sharks (Carcharhinus limbatus and Carcharhinus tilstoni) off north-eastern Australia with species identification inferred from vertebral counts

Precaudal vertebral counts were used to distinguish between 237 morphologically similar Carcharhinus limbatus and Carcharhinus tilstoni and were congruent with differences in reproductive ecology between the species. In addition to differing lengths at maturity and adult body size, the two species had asynchronous parturition, were born at different sizes and the relative frequencies of neonates differed in two coastal nursery areas. Despite evidence that hybridization can occur, these differences suggest the species are largely reproductively isolated.