Extra small virus-like particles (XSV) and nodavirus associated with whitish muscle disease in the giant freshwater prawn, Macrobrachium rosenbergii

A disease of Macrobrachium rosenbergii, the giant freshwater prawn, farmed in China was recently recorded in Zhejiang, Jiangsu, Shanghai, Guangxi and Guangdong provinces. The clinical sign of the disease, which develops in post-larvae (PL), is a whitish appearance of the muscles, particularly noticeable in the abdomen. Mortalities may reach 100% in some hatcheries. Investigations by transmission electron microscopy after negative staining of diseased PL homogenates showed the presence of two types of viral particles: one, unenveloped, icosahedral in shape, 26-27 nm in diameter, the second, much smaller, about 14-16 nm in diameter, designated extra small virus particle (XSV). The large virus has a genome with two pieces of ssRNA (RNA-1 and RNA-2), of 3 and 1.2 kb, respectively. Hybridization tests confirmed that this large virus is closely related to M. rosenbergii nodavirus (MrNV) which was isolated from diseased prawns in a hatchery in the French West Indies. Its very small size and hypothesized biochemical and biological characteristics suggest XSV is a new type of crustacean virus. As XSV has always been found associated with the larger virus (nodavirus) and is located in muscle and connective cells of diseased animals, it could be an autonomous virus, a helper-type virus or a satellite-like virus.     

Immunohistochemical detection of gonadotropin-like material in the hagfish pituitary, correlated with their gonadal conditions

In the present study, immunoreactive gonadotropin (GTH)-like material was examined in the hagfish pituitary, in correlation with their gonadal conditions. For this purpose, three species of hagfish, Myxine glutinosa, Eptatretus burgeri and Paramyxine atami, were used. In all species, GTH-like cells were observed in the adenohypophysis. They were stained with several antibodies to LH-related GTHs, such as ovine LHβ, human LHβ, bullfrog LH, and salmon GTHIIβ. In the subsequent study, the relationship between the amount of GTH-like material and gonadal conditions was examined in Paramyxine atami. The adenohypophysis of adult animals exhibited well-developing features, and about half of the adenohypophysial cells were stained intensely with anti-ovine LHβ. On the other hand, the adenohypophysis of juveniles exhibited less developed features with few or no cells stained with anti-ovine LHβ. These results suggest that a GTH-gonadal system is truly present in the hagfish.     

Transgenic cell lines which stably express progestogen receptors (PRS) α and β and the PR-responsive reporter genes

Transgenic cell lines which stably express progestogen receptors (PRs) and the PR-responsive reporter genes were developed. They are a good system for rapid, sensitive and reproducible screening of various ligands.     

Neurotoxins in a toxic red tide of Heterosigma akashiwo (Raphidophyceae) in Kagoshima Bay, Japan

In April 1995, an unusual large-scale red tide of Heterosigma akashiwo (Hada) Hada occurred, causing massive fish kills in Kagoshima Bay, Japan. Four neurotoxic components, HaTx-i , HaTx-ii a, HaTx-ii b and HaTx-iii , which corresponded to brevetoxin components. PbTx-2. PbTx-9, PbTx-3 and oxidized PbTx-2, were inferred from analysis of Heterosigma red tide toxins on TLC and HPLC.     

The size composition of the eggs of curimbatá, Prochilodus scrofa Steindachner 1881, induced to spawn with human chorionic gonadotropin (HCG)

Curimbatá, Prochilodus scrofa, were examined and selected for induced spawning with human chorionic gonadotropin (HCG). Intra-ovarian eggs were sampled and size composition was analyzed.With 21 females, two doses of HCG were applied at 10-h intervals, 5 IU and 10 IU per gram of total weight. According to response, three distinct groups were identified. For the groups where eggs were successfully fertilized, followed by embryonic development, the percent frequency distribution of egg diameter was unimodal with a constant mode of 1111.15 μm. It is suggested that for P. scrofa, selection of recipient females can be made on egg frequency-diameter distribution.     

Effects of dietary thiamin on the physiological status of the grouper <Emphasis Type="Italic">Epinephelus coioides</Emphasis>

This study was conducted to evaluate the effects of dietary thiamin on the physiological status of the juvenile grouper, Epinephelus coioides. Graded levels of thiamin (0.08, 0.50, 2.12, 3.15, 4.63, 12.37 mg thiamin kg⁻¹ diet) were fed to grouper juveniles (mean weight: 16.97 ± 0.14 g) for 10 weeks. Although fish fed the thiamin-deficient (TD) diet showed no obvious symptoms of thiamin deficiency or increased mortality, those fed the lowest doses of thiamin (0.08 and 0.50 mg thiamin kg⁻¹ diet) had significantly decreased transketolase activity in the liver. In addition, the level of liver thiobarbituric acid reactive substances in fish fed the TD diet was 33–67% higher than that in fish with the thiamin-supplemented diet. There were no significant differences in superoxide dismutase activity between the different groups of fish.     

Effect of dietary iron supplement on growth, haematology and microelements of juvenile grouper, Epinephelus coioides

An experiment was conducted to investigate the effect of dietary iron supplement on growth, haematology and microelements of juvenile grouper, Epinephelus coioides. Casein–gelatine‐based diets supplemented with 0, 50, 100, 150, 200 and 250 mg kg⁻¹ iron from ferrous sulphate were fed to grouper (mean initial weight: 21.0 ± 0.2 g) for 8 weeks. Weight gain was highest in fish fed the diet supplemented with 100 mg kg⁻¹ iron, intermediate in fish fed diets with 50, 150, 200 and 250 mg kg⁻¹ iron and lowest in fish fed the basal diet. Feed efficiency followed a similar trend except that the lowest value was in fish fed the basal diet and the diet supplemented with 250 mg kg⁻¹ iron. Hepatic iron was highest in fish fed diets supplemented with iron ≥100 mg kg⁻¹, followed by fish fed diet with 50 mg kg⁻¹ iron and lowest in fish fed the basal diet. The whole‐body iron was lowest in fish fed the basal diet but not significantly different from other groups, as judged by anova . Iron supplement to the basal diet had no significant effect on haematological parameters (red blood cell count, haematocrit and haemoglobin), hepatic copper concentration or manganese, zinc concentration in liver and whole body. Broken‐line analysis of hepatic iron indicated that iron supplementation of 100 mg kg⁻¹ satisfied the hepatic iron storage and that further supplementation did not expand the iron status.     

Cascading effects of introduced Nile perch (Lates niloticus) on the foraging ecology of Nile tilapia (Oreochromis niloticus)

Abstract –  Nile tilapia ( Oreochromis niloticus L.) is the dominant of the introduced tilapiines in many East African lakes and has flourished in the presence of introduced Nile perch ( Lates niloticus L.). We explored the hypothesis that O. niloticus exhibits increased omnivory in response to a decline in abundance of haplochromine cichlids. First, we quantified variation in habitat use and diet of O. niloticus in Lake Nabugabo, Uganda. Second, we compared the diet of O. niloticus in lakes with (Nabugabo, Victoria) and without (Mburo, Wamala, Nyamusingiri, Kyasanduka) introduced Nile perch. In Lake Nabugabo, a higher level of phytoplanktivory was observed in small juveniles than in larger fish and in wetland ecotone areas where haplochromines were most abundant. An omnivorous diet dominated by detritus and invertebrates was recorded for O. niloticus in lakes Nabugabo and Victoria, while a predominantly herbivorous diet was characteristic of O. niloticus in lakes without Nile perch. Availability of a broad food base in lakes where inshore insectivores have been reduced may explain the increased omnivory recorded in lakes Nabugabo and Victoria.     

Allozyme variation in riverine and lacustrine populations of Macrobrachium nipponense (de Haan)

Abstract. Allozyme variation at 32 protein genetic loci was studied in four populations of Macrobrachium nipponense (de Haan) from two contrasting habitats, wholly freshwater lacustrine sites and brackish water riverine areas from different parts of Asia (Hong Kong, Canton, Wuhan, Japan). The average values of observed heterozygosity were 7·45% for lacustrine and 12·30% for riverine sites, the percentage of polymorphic loci (0·99) was 32·5%. The freshwater/lacustrine populations had lower estimates of genetic variability than the river/brackish water populations. The average genetic similarity and genetic distance (Nei's) were 0·92 and 0·084 respectively. The results were compared with those of the only other study on this species. The implications of these results for this species are discussed.