Triiodothyronine is necessary for the action of growth hormone in acclimation to seawater of brown (Salmo trutta) and rainbow trout (Oncorhynchus mykiss)

Brown (BT) and rainbow trout (RT) in freshwater (FW) were treated with ovine growth hormone (GH), GH + iopanoic acid (IOP), and GH + IOP plus triiodothyronine (T₃) for RT only. After 1 week of treatment, trout were transferred to 30 o/oo SW and treatment continued. In FW, GH treatment increased significantly plasma T₃ level (BT) and T₃/T₄ ratio (BT and RT) by stimulating T₄ to T₃ deiodination. In the GH + IOP group, the plasma T₃ levels and T₃/T₄ ratio fell significantly as T₄ to T₃ deiodination was inhibited. In GH + IOP + T₃-treated RT, plasma T₃ and T₃/T₄ ratios increased significantly relative to other groups. No mortality occurred and plasma osmolarity (PO) was not altered by any treatment in FW. After transfer to SW, all IOP + GH trout died within 2 (BT) or 3 days (RT). All GH-treated or control BT survived to the end of the experiment (6 days). RT survival rates tended to be improved in GH and GH + IOP + T₃ groups relative to controls. Correlatively on day 1 the PO increase was significantly higher in IOP + GH groups (BT and RT) than in the other groups and significantly lower in GH and GH + IOP + T₃ treated RT than in controls from days 1 to 6. These data confirm the requirement of T₃ and deiodination of T₄ to T₃ for the development of hypoosmoregulatory mechanisms in SW as previously shown (Lebel and Leloup 1992). Furthermore, the suppression of the hypoosmoregulatory effect of GH, when conversion of T₄ to T₃ was inhibited by IOP and the reversal when T₃ was added to IOP + GH treatment suggests that GH osmoregulatory action in SW acts via the simulation of T₄-5′ monodeiodination which increases T₃ production.     

Genetic differentiation between anadromous and freshwater resident brown trout (Salmo trutta L.): insights obtained from stable isotope analysis

Abstract –  A genetic survey was carried out on recently emerging fry to investigate interbreeding between anadromous and freshwater resident brown trout in La Roche Brook, a major spawning tributary of the Oir River system (Normandy, France). Emerging fry were sampled at three different sites in spring 2002 and 2003. Stable isotope analysis (SIA) allowed the classification of each individual as the progeny of resident ( N  = 76) or anadromous ( N  = 58) female trout. Microsatellite DNA analysis showed that genetic diversity between fry samples can be explained by microgeographical (various sampling sites) and temporal (2 years of sampling) variations rather than maternal origin (anadromous vs. freshwater resident). We conclude that a high level of gene flow exists between the two morphs when anadromous adults have access to the spawning grounds of residents. We highlight the relevance of using SIA in conjunction with genetic analysis to study interactions between the two morphs.     

Visualizing the early infection of Agathis australis by Phytophthora agathidicida,using microscopy and fluorescent in situ hybridization

Phytophthora agathidicida (PTA) causes a root rot and collar rot of New Zealand kauri (Agathis australis). This study developed techniques to visualize early infection of kauri by PTA in deliberately inoculated seedlings. Conventional light microscopy was carried out on cleared and stained roots using trypan blue to observe PTA structures. Additionally, scanning electron microscopy (SEM) was used to study the PTA root structures at a higher resolution. A fluorescent in situ hybridization assay (FISH) was developed using a PTA‐specific probe to label PTA structures in planta. Infection progression in roots of 2‐year‐old kauri inoculated with PTA at 5, 10, 16 and 20 days post‐inoculation (d.p.i.) was compared using these three approaches. Light microscopy identified no Phytophthora‐like structures in the control treatments. In PTA‐inoculated plants, lignitubers were produced 5 d.p.i. in cortical cells. Infection was localized after 5 days, but as the infection progressed (up to 20 d.p.i.), the ‘degree’ of root infection increased, as did the number of replicates in which structures were observed. SEM provided higher resolution images; again, no PTA structures were observed in the negative control material examined. The slide‐based FISH‐specificity assay successfully hybridized with PTA hyphae. Fluorescence was observed using 330–380 nm excitation and an emission filter at 420 nm (DAPI), with PTA nuclei fluorescing a bright greenish‐yellow. Cross‐reactivity was not observed when the assay was applied to six other non‐target Phytophthora species. Successful hybridization reactions occurred between the primer and PTA structures in planta. Applying this FISH assay has allowed clear differentiation of the intracellular and intercellular structures of PTA. The technique can be applied to longer term studies or analysis of ex situ inoculation studies aiming to elucidate differential host‐responses to the pathogen. Additionally, the technique could be applied to study the interactions with other fungal endophytes (e.g. mycorrhizal fungi), which could be assessed for biocontrol potential as part of the integrated management of the disease.     

Road to shared prosperity: The elaboration and influence of a transboundary policy narrative for regional economic integration

In the Mekong Region, the Asian Development Bank and partners have promoted economic corridors as a way to achieve regional economic integration and growth. This study evaluates how a transboundary policy narrative of shared prosperity around the East–West Economic Corridor programme emerged, and then how it was elaborated and used, taking a set of border policies of the government of Thailand as cases. For two decades the shared prosperity narrative has been used by a coalition of elite actors to support a programme of investments in road infrastructure, as well as to push for agreements on trade, border logistics, investment and tourism. The shared prosperity narrative has helped maintain support for the programme despite its failures to meet projections and expectations. Although criticised by civil society and experts from time to time, no coherent shared counter‐narrative emerged. Policy elites in Thailand have used the transboundary narrative to justify investments in special economic zones, and transport infrastructure near the border and inside neighbouring countries. Thailand has also reproduced the narrative in support of efforts to bolster tourism cooperation, and negotiate cross‐border trade and logistics agreements. Roads and bridges have been built, underlining how discursive practices have material consequences and reinforce the narrative.     

Demographic assessment of a stocking experiment in European Eels

Since the 1980s, the European eels’ stocks have dramatically decreased with no sign of recovery, resulting in their classification as Critically endangered on the IUCN red list of threatened species. The European Council Regulation 1100/2007 requires that 35% of glass eels caught annually by fishing be released in European waters for restocking. However, the efficiency of this measure on population viability has never been evaluated. Here, we estimated demographic parameters of a stocked population of French eels using a multistate capture–recapture model. Using these estimates, we then estimated population size and predicted the number of future genitors obtained by stocking. We found that the stage in which eels were stocked did not influence their future survival and that the maximal number of silver eels was quickly reached, after 3 years following stocking. We concluded that stocking experiments in the Mediterranean region are efficient for fast production of genitors. We suggest that further studies should assess the quality of these genitors.