Muhammad Mehedi Hasan

Background: Sun drying of fish in open air is an age‐old traditional practice in Asia and some other parts of the world. This study aims to suggest optimal field doses of turmeric, pepper, salt and the bacteriocin nisin (food additive, E234) for open‐sun‐dried silver jewfish (Johnius argentatus) under a tropical environment. Investigations were carried out on the blowfly infestation, proximate composition, water reconstitution properties and organoleptic and microbial quality of open‐air‐dried fish samples.Results: A direct relationship between moisture reduction and drying period was observed with salt‐treated samples demonstrating accelerated moisture reduction, reaching as low as 14.1% after 34 h. Turmeric and pepper treatments provided some protection against weight loss but ultimately extended the drying time to 38 h. Botanical pesticides like turmeric or pepper exhibited significant efficacy against blowfly adult and larval infestation with similar efficacy observed in 15% and 25% salt‐treated samples. Proximate composition analysis revealed that salt‐treated samples had lower moisture ranging from 14.1% to 16.0% but higher protein of 58.2%–62.1%, while the lipid and ash content did not vary significantly (p > 0.05). The water reconstitution properties of salt‐treated samples exhibited superior rehydration rates, with the highest in nisin (Niseen S) + 15% salt‐treated samples at 60°C, while organoleptic evaluations revealed salt‐treated samples to possess favourable attributes with minimal insect infestation and broken pieces. Finally, microbial analysis demonstrated the lowest aerobic plate count in dried fish samples treated with nisin (Niseen S) alone or in combination with 15% salt and/or 3% turmeric ranging from 3.97 ± 0.20 to 4.33 ± 0.07 log cfu/g.Conclusion: It is concluded that 200 ppm nisin (Niseen S)‐treated samples in combination with 3% turmeric and/or 15% salt are a viable option for producing high‐quality dried fish in traditional open‐air sun‐drying practices.

Schistosomiasis is a neglected tropical disease (NTD) caused by blood flukes (Schistosoma spp.). Schistosomatids affect a wide array of vertebrate hosts, including humans. In the present study, multiple species of schistosomatids were identified by isolating schistosomatid cercariae (SC) from naturally infected snails. We also described different biotic and abiotic factors influencing SC infections in snails and reported human cercarial dermatitis (HCD) for the first time in Bangladesh. A total of 22,012 snails of seven species: Lymnaea auricularia, L. luteola, Indoplanorbis exustus, Physa acuta, Viviparus bengalensis, Brotia spp., and Thiara spp., were collected and examined. Among these snails, 581 (2.6%) belonging to five species: L. luteola, L. auricularia, P. acuta, I. exustus, and V. bengalensis, were infected with SC. The rate of infection was the highest for L. luteola (11.1%), followed by L. auricularia (5.3%), and was the lowest for V. bengalensis (0.4%). Prevalence in snails was the highest in September (16.8%), followed by October (9.5%) and November (8.8%), and was the lowest in colder months, such as January (1.8%) and February (2.1%). Infections with schistosomatids were more common in larger snails and snails collected from sunny areas. We confirmed the presence of Schistosoma indicum, S. incognitum, S. nasale, S. spindale, and Trichobilharzia szidati by PCR and sequencing. Through a questionnaire survey, we detected HCD in 214 (53.5%) individuals, and the infection rate was almost equally distributed across all professions. Collectively, the present results suggest that lymnaeid snails are the main vector for Schistosoma spp. prevalent in Bangladesh, and schistosomatids with zoonotic potential are also prevalent.

Recombinant expression system was established for rainbow trout myoglobin (Mb) considering its unique primary structure of having one unusual deletion and two cysteine residues in contrast to the other fish Mbs. The obtained recombinant Mb without His-tag showed non-cooperative thermal denaturation profile. The presence of free cysteine residue(s) in rainbow trout Mb was demonstrated by reacting with a sulfhydryl agent, 4, 4´-dithiodipyridine, which ultimately resulted in the oxidation of Mb with characteristic changes in visible absorption spectra. Besides, the recombinant Mb displayed steady peroxidase reactivity indicating in vivo roles of Mb as a reactive oxygen species scavenger. The findings of the present study indicate that the solitary rainbow trout Mb, which ultimately manifest typical secondary structure pattern and corroborate characteristic functionality, can be over expressed in recombinant system devoid of fusion tag.

Although myoglobin (Mb) has been considered to be one of the well-characterized proteins, screening of post-genomic era databases revealed the lack of adequate information on teleost Mbs. The present study was aimed to investigate stability and functional features of Mbs from three teleosts of the same family. To unfold how primary structure influences the stability and function of proteins, Mbs were purified from the dark muscles of three carangids, namely, yellowtail, greater amberjack, and silver trevally. Thermostabilities measured by circular dichroism (CD) spectrometry revealed species-specific thermal denaturation pattern, i.e., silver trevally > yellowtail > greater amberjack Mbs. On the other hand, autoxidation rate constants of the ferrous forms of those three carangid Mbs showed positive correlation between the ferrous state of the heme iron and rising temperature. The order of autoxidation rate was in the order of greater amberjack > yellowtail > silver trevally Mbs. The finding of the present study denotes that the thermal stability is not necessarily correlated with the functional stability of carangid Mbs even though their primary structures shared high homology (84–94%).