The life cycle of the heterophyid fluke, Haplorchis pumilio is elucidated for the first time from the Indian region. Various stages in the life cycle were established based on observations made on natural infections found in snails and fish in a freshwater stream at Visakhapatnam, India and experimental infections carried out in the laboratory. The thiarid snail, Thiara tuberculata served as the first intermediate host and a wide range of freshwater fish as second intermediate hosts. Natural infections with adult flukes were found in the piscivorous birds Ardeola grayii and Bubulcus ibis. Adults were raised experimentally in day-old chicks. Distinguishing features of the cercaria of H. pumilio are: a large body size (200–224×92–96 μm), body–tail ratio of 1:2.1 and densely distributed pigment granules in the parenchyma imparting a brownish tinge to the body. Natural infections with metacercariae were found in the freshwater fish Channa punctatus, C. orientalis, Puntius sophore, Gambusia affinis and fingerlings of Cyprinus carpio and Liza macrolepis. Additionally, experimental infections were established in Therapon jarbua, Esomus danricus and Oreochromis mossambica. Metacercariae were embedded in the caudal muscles of fish and heavy infections induced mortality. Metacercariae were infective at about 15 days of age.

An analysis is made of the community structure of the helminth parasites of the tuna Euthynnus affinis collected off the coast of Visakhapatnam, Bay of Bengal. The helminth fauna comprised 23 species, consisting of two monogeneans, 18 digeneans, one larval cestode, one nematode and one acanthocephalan. Didymozoids, represented by 14 species, were the dominant members of the parasite spectrum. The parasite assemblage is characterized by species richness as well as a high diversity. Most of the parasites found, the didymozoids in particular, were host specialists, exhibiting a high degree of host specificity. The fauna comprised three core species, four satellite species and many secondary species, with no potential for interaction among them but the degree of predictability is high in that each infracommunity comprised two or three core species superimposed by a few secondary species. Many host factors such as the varied diet, high vagility, long life span and endothermy appear to have contributed to the development of the species rich and diverse parasite communities in the tuna. There was evidence for a decrease in parasite density and an increase in diversity with increase in host size, indicating that host size has a profound influence on the component community structure.

Spatially resolved transcriptomics (SRT) is a growing field that links gene expression to anatomical context. SRT approaches that use next-generation sequencing (NGS) combine RNA sequencing with histological or fluorescent imaging to generate spatial maps of gene expression in intact tissue sections. These technologies directly couple gene expression measurements with high-resolution histological or immunofluorescent images that contain rich morphological information about the tissue under study. While broad access to NGS-based spatial transcriptomic technology is now commercially available through the Visium platform from the vendor 10× Genomics, computational tools for extracting image-derived metrics for integration with gene expression data remain limited. We developed VistoSeg as a MATLAB pipeline to process, analyze and interactively visualize the high-resolution images generated in the Visium platform. VistoSeg outputs can be easily integrated with accompanying transcriptomic data to facilitate downstream analyses in common programing languages including R and Python. VistoSeg provides user-friendly tools for integrating image-derived metrics from histological and immunofluorescent images with spatially resolved gene expression data. Integration of this data enhances the ability to understand the transcriptional landscape within tissue architecture. VistoSeg is freely available at http://research.libd.org/VistoSeg/.

Bell pepper or sweet pepper (Capsicum annuum L. var. grossum) is highly susceptible to high-temperature stress (HT). Hence, search for donor across C. annuum for HT tolerance was undertaken by following Temperature Induction Response (TIR) technique. The induction and challenging temperature requirement for TIR screening were standardized in 1 d-old Capsicum seedlings. Forty Capsicum genotypes were evaluated based on the recovery growth (RG) and per cent reduction in recovery growth (%RRG) of the seedlings. The genotypes Punjab Guchhedar and Ajeet 1 were found to have maximum cellular level tolerance (CLT) to HT with higher RG and lower %RRG compared to the non-induced seedlings and HDC 75 was found to have minimum CLT. In order to confirm the findings, another experiment was conducted under managed stress and control conditions. Absolute yield obtained from both the environments were used to calculate stress tolerance indices such as heat susceptibility index, tolerance index, stress tolerance index, mean productivity, geometric mean productivity and yield stability index. Based on these tolerance indices, Punjab Guchhedar and Ajeet 1 were found to be highly tolerant and HDC 75 as highly susceptible. Further, the combined result of TIR and tolerance indices also gave the same result confirming Punjab Guchhedar and Ajeet 1 can be used as a donor for the future breeding programme aimed at evolving high-temperature-tolerant bell pepper cultivars. The result also confirms the fitness of TIR technique to screen Capsicum genotypes for tolerance to HT based on variability in acquired thermotolerance.

The miracidium of Transversotrema patialense (Digenea: Transversotrematidae) has 21 epidermal cells arranged in four tiers with an epidermal formula of 6, 9, 4, 2. The penetration gland is large, conspicuous, contains a posterior globular part with 6 prominent nuclei and opens out through 6 pores arranged in two lateral groups at the tip of the apical papilla. The miracidium lacks lateral papillae, possesses a well developed subepithelium, a pair of flame cells and a germ ball.

The life history of Grysoma indica n.sp., a psilostome trematode, obtained experimentally in ducklings, after feeding with metacercariae occurring in the snail Thiara tuberculata, is elucidated. Natural infections with cercariae were found in T. tuberculata, collected from a freshwater stream at Visakhapatnam, India. Metacercarial cysts were found in the same and other species of snails in the locality. The new species differs from other species of the genus in the sucker proportions, position of the testes and distribution of the vitelline follicles.

Metacercariae identified as those of the heterophyid trematode, Galactosomum ussuriense were collected from 3 species of brackish water fishes from Bheemunipatnam. The organization of the the larva is described in detail. This is the first record of the metacercaria of this species although the adult has not so far been recorded from India.

The life cycle of Genarchopsis goppo a hemiurid trematode found in the stomach of Channa punctata has been worked out in detail. The egg contains a fully developed miracidium at the time of liberation. The miracidium contains a ciliated covering, a long apical gland and a crown of spines at the anterior end. The snail Amnicola travancorica acts as the first intermediate host inside which the miracidium passes through sporocyst and redial generations. The cercaria is of cystophorous type and is identical to Cercariae Indicae Sewell XXXV. Metacercaria occurs in the ostracods Stenocypris malcolmsoni and Eucyoris capensis. The fish Aplocheilus panchax serves as the paratenic host. The entire developmental cycle from egg to egg producing adult takes 3 months.

Adult trematodes identified as Galactosomum ussuriense Oshmarin, 1963 were recorded from the intestine of Sterna hirundo and Larus brunnicephalus from Visakhapatnam, India. The occurrence of metacercaria of this species in inshore and offshore fishes is discussed in relation to the ecology of the snail intermediate host.

The life history of Allocreadium fasciatusi which occurs in the intestine of a freshwater fish Aplocheilus melastigma has been worked out in detail. The snail Amnicola travancorica acts as the first intermediate host. The miracidium hatching out from the eggs attacks the snail and passes through two generations of rediae. Cercariae are of ophthalmoxiphidiocercous type with very long tail and are identical to Cercariae Indicae XLIX Sewell, 1922. The cercariae penetrate and develop into metacercariae in the haemecoel of the copepods Mesocyclops leuckarti, Microcyclops varicans and Marcocyclops distructus. Upon ingestion by the definitive host, the metacercariae excyst and develop into adults. All the stages in the life cycle are described and the life cycle is compared with other allocreadiid life cycles. The original description of A. fasciatusi is revised and Psilostomum chilkai Chatterji, 1956 from Lates calcalifer is synonymized with it.

The effects of crowding on growth, reproduction, rate of recovery and site of infection of Philophthalmus nocturnus were investigated by infecting various groups of day-old chicks with 25, 50,75, or 100 excysted metacercariae and examining them at 10 or 25 days post-infection. Considerable reduction in the body length and the size of the gonads was noticed in flukes grown under crowded conditions. Crowding also caused some change in the habitat of flukes, but had no effect on their rate of recovery. Very few flukes reached the ovigerous stage under overcrowded conditions and none reached the embryonated larval stage.

Lobatostoma hanumanthai n.sp. is described from the intestine of the carangid Trachinotus blochi from Bay of Bengal. It anatomical characters are compared with previously described species in the genus. This is the first record of an aspidogastrean from marine fishes of the Indian region.

Magnacercous cercariae with heavily pigmented tails and possessing a pair of eyespots and seven pairs of penetration glands, some of which are para vesicular, were found to develop in the prosobranch gastropod, Cerithium coralium collected from a brackish water locality at Bheemunipatnam, A. P. India. The cercariae developed into metacercariae of Galactosomum ussuriense in the viscera of the fish Therapon jarbua. Successive stages in the development of metacercaria from the cercaria were followed. Natural infections with metacercariae were found in T. jarbua, Valamugil cunnesius and Megalops cyprinoides. The definitive host of G. ussuriense in the present area of investigation is still not known. This represents the second account of part of a life-cycle in the genus Galactosomum.

Fifty day-old chicks were each infected with 10 excysted metaccreariae of Philophthalimus nocturnus Looss. 1907 around each orbit and growth, development and allometry were studied. The growth rate showed two phases over a period of 35 days, a limited lag phase lasting two days post-infection in which flukes did not exceed 440 μm in length, and a rapid phase during which growth was rapid and flukes reached a size of 3·008–3·504 mm on day 35. Five developmental stages were noticed during the course of development of the metacercaria to the egg-producing adult stage. Eggs appeared in the uterus on day 14 and oculate miracidia on day 25. The hindhody, testes and ovary showed positive allometric growth, the pharnyx less so, whereas negative allometric growth was shown by the forebody. Body width, oral sucker and ventral sucker were close to isometry, growing at the same rate as the body length.

The vegetative and sporogonic stages of Unikaryon allocreadii sp. nov. and Nosema gigantica sp. nov., from the parenchyma of adult flukes, Allocreadium fasciatusi in the gut of the freshwater fish Aplocheilus melastigma from India, are described and figured. U. allocreadii, which is uninucleate throughout development and is disporoblastic, differs from U. legeri in that it occurs in adult flukes from a freshwater host. N. gigantica has diplokaryon nuclei, at least in the sporogonic stages, and is much larger than all other microsporidia in platyhelminths.

Hatching of the spores and patholgenicity are described and the mode of transmission to the flukes is discussed. Infected flukes, which are sluggish and opaque, are often displaced from the normal site of infection.

Heterogeneity in susceptibility of guppies (Poecilia reticulata) to infection with Gyrodactylus bullatarudis was examined by comparing the establishment, reproduction and survival of the parasite on 4 inbred strains of the fish host following low and high levels of exposure to infection. The 4 strains fell into 2 broad categories of innately ‘resistant’ and ‘susceptible’ fish on the basis of strain differences in (a) the rates of growth and decay of the parasite populations, (b) the proportional occurrence of susceptible and resistant fish within each strain, (c) the average duration of primary infection, and (d) the duration of resistance to reinfection following recovery from a primary exposure. The results suggest genetic control of resistance/susceptibility traits and experiments with hybrids tentatively suggest dominance of resistance over susceptibility. The potential of the guppy – Gyrodactylus laboratory system for the investigation of the role of genetic factors in the study of host–parasite interactions is discussed.

The population biology of Paradistomum orientalis, a dicrocoeliid trematode occurring in the gall bladder of the garden lizard Calotes versicolor, was investigated during 1991-1993. The prevalence and abundance of the fluke were high throughout the year and demonstrated no seasonal fluctuations. The maturation cycle of the fluke followed an annual pattern. The recruitment of the fluke was restricted to the period September to February, with a peak during September. Mature flukes occurred throughout the year, facilitating continuous release of eggs into the macroenvironment. Rainfall plays a major role in governing the maturation cycle, by regulating the population density of the snail host and the feeding activity of the definitive host. The frequency distribution of the fluke followed the overdispersion pattern, fitting the negative binomial model. There is no evidence for the existence of parasite-induced host mortality. On the other hand, competition for space and nutritive resources under crowded conditions serves as a major regulatory force and is the key factor responsible for maintaining the equilibrium of parasite densities during different months. The infrapopulation of the fluke remained stable over several years.