Fish culture in rainfed rice fields of northeast Thailand

Adoption of rice-fish culture by farmers in the rainfed areas of northeast Thailand is examined with reference to recent field research and extension in the region. The practice is placed in perspective with the development of aquaculture per se and the human and agricultural ecology of this heterogeneous region. Rice-fish culture is a recent activity in the region and has been promoted by government and non-government agencies with variable success among small-scale farmers. The widespread availability of private hatchery-produced fish seed and perceived decline in wild fish have been important stimuli. Rainfed rice fields are marginal agricultural environments and lack of water constrains both rice and fish production. Wild swamp fish are tolerant of these conditions and traditional systems for their management and capture have expanded greatly in recent years. In much of the region ‘trap’ ponds are used more for catching wild fish than as refuge sumps or ponds for fish culture per se; wild fish typically constitute between 20 and 80% of the total yields in stocked systems. Widespread availability of fish seed allows more farmers to try rice-fish culture but the small size of seed at purchase is still a problem particularly where carnivorous, wild fish are prevalent. Appropriate on-farm nursery techniques may improve success and adoption of hapa nursing has been high in some parts of the region. Species ratio and density of fish stocked depends mainly on their availability from fry traders; the major species stocked in rice fields are the silver barb (Puntius gonionotus), common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus).

Farmers adapt rice fields for fish culture as part of their whole farm strategy; benefits to rice, vegetable and fruit and livestock may be considered more important than fish yields. The high value attached to even small quantities of fresh fish is a major incentive for rice-fish culture, but women who are decision makers in terms of changes to rice fields and household consumption have often not been fully considered during promotion of rice-fish.

The relatively small areas of riceland that farmers can stock and harvest fish, low yields per unit area and high consumption of fish reduces the importance of rice-fish culture in many rural households. The analysis suggests that stocking fish in rice fields in areas with poor access to wild fish supplies from community water bodies would have most impact.

Although rice-fish culture can contribute to subsistence requirements, the high labour demand often means that intensified capture of wild fish or pond-based culture of fish are more attractive for poorer and better off farmers, respectively.     

Estimating stock depletion level from patterns of catch history

The degree to which a stock is depleted is one of the most important quantities in fisheries management because it is used to quantify the success of management and to inform management responses. However, stock depletion is extremely difficult to estimate, particularly with limited data. Using the RAM Legacy database, we developed a boosted regression tree (BRT) model to correlate depletion with a range of predictors calculated from catch data, making the model usable for many fisheries worldwide. The most important predictors were found to be catch trends obtained from linear regressions of scaled catch on time, including regression coefficients for the whole catch time series, the subseries before and after the maximum catch, and in recent years. Eight predictors explain about 80% of variation in depletion. There is a correlation of .5 between measured levels of depletion and the predictions of the BRT model. Predictions are less biased when the stock is fished down below half of the carrying capacity. The BRT model outperforms comparable existing catch‐based depletion estimators and could be used to provide priors for depletion for data‐poor stock assessment methods, or used more directly to provide estimates of the probability that depletion is below a given threshold value.     

Effects of culture conditions on larval growth and survival of stalked barnacles (Pollicipes pollicipes)

Pollicipes pollicipes (Crustacea: Scalpelliformes) is a highly prized food in Portugal and Spain and consequently a species of considerable interest to aquaculture. Surprisingly, however, larval culture conditions for this barnacle have not been optimized. This study investigated the effects of temperature, diet, photoperiod and salinity on the growth and survival of P. pollicipes larvae. Temperature had a significant effect on specific growth rate (2.6–5.9% total width per day, from 11 to 24°C), reducing mean development time to the cyprid from 25 days at 11 °C to 10 days at 24°C, although this was accompanied by a significant increase in mortality to over 90% above 22°C. Mid‐range temperatures (15–20°C) maximized total survival (19–31% respectively). Algal diets of Tetraselmis suecica, T. suecica/Skeletonema marinoi and S. marinoi/Isochrysis galbana did not affect specific growth rate significantly, but survival (on average 39% in 15 days) and the proportion of high‐quality healthy cyprids was significantly higher on the latter two diets (11–15% of initial number of larvae). Photoperiod did not significantly affect the survival, although specific growth rate was significantly higher at 24:0 and 16:8 L:D. Salinity (20–40 g L^?1 range) did not affect growth and survival significantly. The best growth and survival were accomplished using rearing temperatures of 15–20°C, daily feeding with T. suecica/S. marinoi or I. galbana/S. marinoi and a photoperiod of 24:0 L:D.     

Effect of neuroactive compounds on larval metamorphosis of New Zealand geoduck (Panopea zelandica)

We present here the first laboratory study on the effects of pharmacologically active compounds on the larval metamorphosis of the New Zealand geoduck, Panopea zelandica (Quoy and Gaimard, 1835). Two batches of competent hatchery‐reared larvae were exposed to acetylcholine chloride, epinephrine hydrochloride and excess potassium ions in the form of KCl and K₂SO₄. None of the tested chemicals increased the proportion of metamorphosed geoducks, and in some cases, the chemical caused significant mortality, despite having been used extensively with other species, such as mussels and oysters. This might indicate that geoduck larval physiology and development differs from other bivalves. Geoducks may have evolved distinct chemoreceptor patterns that facilitate metamorphosis under environmentally favourable conditions for subtidal soft sediment habitats suitable for burrowing. Thus, further research is needed to identify alternative cues (e.g. conspecific adults, sediment characteristics and surface biofilm) and understand their role in settlement and metamorphosis. This information will aid the design of reseeding methods and contribute to the development of reliable hatchery production of geoduck spat.     

The fatty acid compositions of established fish cell lines after long-term culture in mammalian sera

The effect of long-term culture of fish cells in mammalian serum on the phospholipid fatty acid composition was investigated. All the cell lines studied had much lower levels of polyunsaturated fatty acids (PUFA) than those found in intact fish tissues. In particular (n-3) PUFA were considerably depleted in the cultured cell lines, leading to very low (n-3)/(n-6) ratios in all the phospholipid classes. In general the cells were rich in 18:1, 16:0, 18:0 and 16:1 with 20:4(n-6) and 22:6(n-3) as the major PUFA. The fatty acid composition reflected the composition of the fetal calf serum added to the media rather than their fish tissue origins. The results were discussed in relation to the roles of PUFA in general cell metabolism and more specifically the role of (n-3) PUFA in fish cells.     

Feline lung-digit syndrome: unusual metastatic patterns of primary lung tumours in cats

PRACTICAL RELEVANCE: Feline 'lung-digit syndrome' describes an unusual pattern of metastasis that is seen with various types of primary lung tumours, particularly bronchial and bronchioalveolar adenocarcinoma. Tumour metastases are found at atypical sites, notably the distal phalanges of the limbs; the weightbearing digits are most frequently affected, and multiple-digit and multiple-limb involvement is common. Often primary lung tumours in cats are not detected because of clinical signs referable to the primary tumour; rather, many cases present with signs referable to distant metastases. Other sites of metastases from feline primary lung tumours include the skin, eyes, skeletal muscle and bone, as well as multiple thoracic and abdominal organs. These lesions are thought to arise from direct arterial embolisation from the tumour. Indeed tumour embolisation to the aortic trifurcation is possible. PATIENT GROUP: Primary lung neoplasms are uncommon in the cat. Older animals are most affected (mean age at presentation 12 years, range 2-20 years). There is no apparent sex or breed predilection. CLINICAL CHALLENGES: Feline lung-digit syndrome presents a diagnostic challenge. Typically there is swelling and reddening of the digit, purulent discharge from the nail bed, and dysplasia or fixed exsheathment of the associated nail. While these signs might be suggestive of infection, this could be secondary to a digital metastatic lesion, particularly in a middle-aged or elderly cat. Radiographic evidence of extensive bony lysis of the distal phalanx, which can be trans-articular to the second phalanx, raises the index of clinical suspicion for metastasis of a primary pulmonary tumour. Thoracic radiography is warranted prior to any surgery or digital amputation as the prognosis is generally grave for cats with this syndrome, with a mean survival time of only 58 days after presentation. EVIDENCE BASE: This article reviews the previous literature and case reports of feline lung-digit syndrome and feline primary pulmonary neoplasia in general, discussing the course of this disease and the varying clinical presentations associated with different sites of metastasis.     

Efficacy of fluorescent calcein mark retention and identification in endangered Colorado pikeminnow Ptychocheilus lucius

Distinguishing hatchery‐reared fishes from wild conspecifics can be required to quantify the success of augmentation programmes. This study estimated the probability of identifying calcein‐marked, hatchery‐reared Colorado pikeminnow Ptychocheilus lucius Girard from external and internal structures. Both control and marked fish held in the laboratory were correctly identified 80% of the time after 300 days. A fluorometer was more accurate 180 days post‐marking, whereas visual observation was more discriminating at 300 days. There were no differences in detection rates among structures in laboratory fish, and for most structures of fish held outdoors, detection rates were <20%. Overall, a strong negative effect of light on mark persistence was observed. Also, an initial positive effect of fish size on mark fluorescence and a negative effect of fish growth were detected. These results suggest the potential use of calcein as a batch‐marking tool would be aided by future studies that better quantify light exposure and calcein mark persistence in both field and experimental settings.     

Synergistic induction of wheat stem rust appressoria by chemical and topographical signals

The leaf alcohols cis -3-hexen-1-ol and trans -2-hexen-1-ol have been previously shown to induce the wheat stem rust (Puccinia graminis f. sp. tritici) to differentiate appressoria in a complex axenic culture medium. In this paper, the possible role of these chemicals in appressorium induction during infection has been analysed further. The inductive potential of ethylene and three cutin monomers were also tested because they have been found to induce appressoria in other fungi. Both hexenols were found to be inductive in aqueous solution in the absence of media constituents. 0.5–1 m trans -2-hexen-1-ol was the most inductive resulting in a maximum of 51% appressorium differentiation. trans -2-hexen-1-ol was also shown to be inductive in vapour form. In aqueous solution, trans -2-hexen-1-ol acted synergistically with topographical signals by increasing the rate of appressorium induction. Combining the two signals also increased the total number of appressoria differentiated (88%). The other chemicals tested were non-inductive although a biochemical domain rich in exposed cutin was localized around stomatal apertures of wheat leaves. The characteristic bipolar morphology of appressoria formed over stomata was found to be determined by topographical signals. Overall, our data support a role for both chemical signals (hexenols or their analogues) and topographical signals being involved in appressorium induction by wheat stem rust.