Two New Records of Snapper(Perciformes, Lutjanidae) from Saint Martin's Island, Bangladesh

The present work documented two snapper species, Lutjanus fulvus Forster, 1801 and Lutjanus erythropterus Bloch, 1790, recently collected from the Saint Martin's Island, Bay of Bengal, Bangladesh, during a survey on coral associated fishes of Bangladesh from July 2017 to September 2018. These two species were identified with morphological characteristics and by analyzing partial mitochondrial COI sequences. The document also included an updated checklist of snappers available in Bangladesh.

Reproductive Isolating Mechanisms in the Bangladesh Coastal Bullfrog Hoplobatrachus litoralis and Its Congeneric Species Revealed by Crossing Experiments and Examination on Spermatogenesis of the Hybrids

To elucidate reproductive isolating mechanisms in the Bangladesh coastal bullfrog Hoplobatrachus litoralis and its congeneric species, we performed crossing experiments using three species： H. litoralis, H. tigerinus and H. rugulosus. In addition, we conducted histological observations on spermatogenesis of the hybrids. The reciprocal hybrids between H. litoralis and H. tigerinus developed normally with somewhat lower viability at the metamorphosis stage compared with the controls. Most of the metamorphosed frogs became mature. On the other hand, almost all hybrids between female H. rugulosus and male H. litoralis or H. tigerinus died of underdevelopment at the tadpole stage, and only a few hybrids metamorphosed normally and survived to maturity. The inner structures of the testes of the control H. litoralis and H. tigerinus were completely normal, with seminiferous tubules filled with compact bundles of normal spermatozoa. Those of the reciprocal hybrids between H. litoralis and H. tigerinus were almost normal or slightly abnormal, with seminiferous tubules that contained pycnotic nuclei in addition to normal bundles of normal spermatozoa, which demonstrates slight abnormalities in spermatogenesis. In contrast, the hybrids between female H. rugulosus and male H. litoralis or H. tigerinus had no bundles of spermatozoa nor spermatids in the seminiferous tubules, which indicates entirely abnormal spermatogenesis. Meiotic chromosome figures in the reciprocal hybrids between H. litoralis and H. tigerinus showed slight abnormalities, with the occurrence of univalents and increase of rod-shaped bivalents. These results indicate that H. litoralis and H. tigerinus are not isolated from each other by hybrid inviability nor by hybrid sterility, although the hybrids showed somewhat abnormal spermatogenesis in hybrids and that H. rugulosus is isolated from both H. litoralis and H. tigerinus by incomplete hybrid inviability and complete hybrid sterility.

Repercussion of salinity on hematological parameters and tissue morphology of gill and kidney at early life of tilapia

This study was attempted to reveal the changes in three hematological parameters such as blood hemoglobin,number of white blood cells(WBCs)and number of red blood cells(RBCs)and one biochemical(e.g.,glucose)parameter along with the changes in histomorphological structures of gills and kidney of Nile tilapia fry reared in saline water.Two experimental set up were used for two different age groups-5 days-after-hatch(5DAH)and 15 days-after-hatch(15DAH)-to test a novel hypothesis:if a little difference in the age during the first exposure to saline water could produce any variation in the results.They were placed into 6 plastic drums having six different salinity levels:0,5,10,15,20 and 25.After 60 days,at least 5 individuals were taken out from each drum to observe the above-hematological and histomorphological parameters.A two-way-ANOVA revealed that,except for hemoglobin,all the observed parameters have been affected the effect of age×salinity interaction(P<0.05).Between the two age groups,only the overall average glucose value and RBC count were significantly different.Among various salinity levels,only RBC and WBC counts differed significantly.Further,the mean glucose value,RBC counts and WBC count at different salinities differed significantly from the base mean value of each parameter.With regard to the histomorphological structure of the gills and kidney,various malformations were evident.Though hypertrophy,epithelial uplifting and epithelial necrosis were present as gill degenerations,hyperplasia was prevalent across almost all salinity levels.On the other hand,glomerular necrosis,pyknotic nucleus,hyaline droplets degeneration,shrinking of the glomeruli,etc.were observed in kidney structures.By assisting to understand the effects of salinity stress,all these data on tilapia fry will help to determine the prospects and scope of culturing the species in high-salinity water.

Intraspecific morphometric diversity of barramundi (Lates calcariferBloch, 1790) in the waters of southern Bangladesh

A total of 160 barramundi's (Lates calcarifer Bloch, 1790) sampled from four rivers (Tentulia, Balaswar, Bakkhali, and Andarmanik) along the southern coastal region of Bangladesh were investigated in terms of morphometric characters to reveal the intraspecific variation. Twenty-five morphometric measurements were extracted using the conventional method and subjected to multivariate analyses (i.e., principal component analysis (PCA), discriminate function analysis (DFA), cluster analysis (CA)) to distinguish individuals from different rivers. The result demonstrated that twenty-two out of 25 measurements was statistically significant (Univariate ANOVA) among all four populations. PCA analysis of morphometric characters resulted in two principal components, PC I and PCⅡ which accounted for 79.25% and 4.28% of the total data variance. PC I-PC Ⅱ plot explained 83.53% of total variance differentiated the population of L. calcarifer into two groups. Discriminate analysis correctly classified about 88.1% of the examined fish into the four areas. The UPGMA dendrogram showed that Bakkhali populations were the most morphologically different populations in comparison to other populations, while Andarmanik and Balaswar populations were very close to each other. The strong morphometric variation between Bakkhali and Tentulia, Andarmanik and Balaswar was observed in the present study, suggested the evidence of the separate stock population of barramundi in these locations, which might require distinct stock management strategies for resource sustainability in the waters of southern Bangladesh. However, if these findings are supported by further molecular markers and geometric morphometry, this would be a strong indication of different stocks of this population in the four rivers of southern Bangladesh.

Variation in the life-history traits of a Schilbid catfish,Clupisoma garua (Hamilton, 1822) in the coastal waters of southern Bangladesh

For the first time,the present study reports the life-history traits,comprising length-frequency distribution(LFD),sex ratio(SR),length-weight relationships(LWRs),condition factors(CFs),and relative growth(W_R),of Clupisoma garua in the coastal waters of Bangladesh.A total of 150 specimens ranging from 8.60 to 25.20 cm total length(TL)and 4.26 to 128.80 g body weight(BW)were collected using traditional fishing gear from August 2013 to July 2014.The overall sex ratio of males to females in the study did not dif fer significantly from the expected value of 1:1(χ~2=0.96,P<0.05)but there were significant sex differences(P<0.05)in the intercepts and slopes of graphs characterizing traits in C.garua.The calculated bvalues for the LWRs were 2.955,2.893 and 2.927 for males,females and combined sexes,respectively,and there was negative allometric growth in all cases(b<3).The condition factors(K_A,K_F,K_R)and relative growth(W R)also did not differ significantly(P<0.05)between the sexes.This study provides a useful tool for fi shery specialists to evaluate the relative condition of fish and to initiate early management strategies and regulations for the sustainable management of the remaining stocks of this species in the entire coastal region of southern Bangladesh.

Assessment of genetic diversity, detection of strain-specific single nucleotide polymorphisms and identification of the Bangladesh and Vietnam strain of Channa striata by PCR-RFLP analysis of the mitochondrial COI gene fragment

Striped snakehead(Channa striata)has enormous fisheries and aquaculture importance due to its high market demand and food value.Recently,Vietnam strain of the species has been introduced to Bangladesh for aquaculture.Therefore,it is essential to develop a reliable molecular technique that can distinguish the Bangladesh strain from the Vietnam ones as biological invasion by feral exotic fish to the wild may cause enduring damage to ecosystem and species diversity.Fin clips from snakehead samples were collected from six locations and total DNA was extracted.The cytochrome oxidase c 1(COI)gene fragment was amplified by PCR using the Fish F1/R1 primer set and sequenced for analysis of intra-and inter-strain genetic diversity and detection of single nucleotide polymorphism to distinguish the Vietnam strain from Bangladesh ones.A total of 15 haplotypes were identified with an overall haplotype diversity of 0.888.The median-joining network created based on COI gene sequences clearly differentiated the Bangladesh strain from the strain of Vietnamese origin by a total of 18 single nucleotide polymorphisms.An In silico restriction analysis revealed AluI was the most suitable restriction enzyme that produced diagnostic restriction profiles of the two strains of C.striata.PCR-RFLP analysis by the restriction enzyme AluI created distinguishing restriction profile similar to that in the In silico analysis.This work illustrates a simple,reliable and inexpensive molecular tool for the identification of the Bangladesh and Vietnam strains of C.striata by one-step PCR and restriction of the COI gene fragment.

An overview of freshwater prawn fishery in Bangladesh:present status and future prospect

The freshwater prawn fishery plays an important role in the economy of Bangladesh.The fishery is mainly based on the culture of Macrobrachium rosenbergii.The culture fishery has been growing rapidly,thus,masking the dwindling capture fishery which is faced with serious environmental issues augmented by deleterious fishing methods.Despite the high prospects of the freshwater prawn aquaculture in Bangladesh,a lot of research is needed to ensure the sustainable development of the capture fishery which forms a key source of prawn aquaculture seed as well as provide a baseline for future appraisals.Freshwater prawn aquaculture in Bangladesh is based on traditional methods with continuous adaptations by the rural fishers.However,numerous constraints to its full development are evident at all stages of its production.Lack of quality brood stock,seed,feeds and poor technical knowledge at farmers level are but some of the impediments challenging the sustainability of this industry.This paper reviews the freshwater prawn fishery of Bangladesh over the last few decades and outlines approaches for the development of an ecosystem-based management of both the culture and capture sectors of this important fishery.

Effects of antibiotic on the bacterial microflora in two commercially important catfish species,Clarias batrachus and Heteropneustes fossilis in Bangladesh

Objective:To assess the effects of a widely used antibiotic,oxytetracycline(OTC)on the bacterial microflora in two catfish species under artificial culture conditions in the laboratory.Methods:The experiment was conducted in the Faculty of Fisheries,Bangladesh Agricultural University,Mymensingh-2202.The fish were reared in six aquaria(size 37 cm×30 cm×60 cm)where three aquaria served as replicates of the antibiotic treatment groups and the remaining three aquaria served as an untreated control group.Each aquarium was stocked with 25 fish on an average body weight 15 g.OTC was administered to the fish in the treatment groups at the rate of 2 g/kg in-feed twice daily upto ad libitum,whereas fish in the untreated control groups were given the same feed without antibiotics for 20 d.During the experiment,bacterial loads were estimated as colony forming unit(CFU/g)by every alternate day in the aquarium water,gills,skin and intestine of fish.Results:The administration of OTC in feed resulted in gradual decrease of bacterial loads in the gills,intestine and skin of the two catfish species tested.In contrast,the bacterial loads remain unchanged or slightly increased in the control groups not fed with OTC.Water quality parameters such as dissolved oxygen,pH and total hardness were found to be within suitable range in the test aquaria but not in control aquarium throughout the experimental period.Conclusions:The results of this experiment showed that in-feed antibiotic OTC for a period of 20d reduced the bacterial loads in the gills,intestines and skin of treated fish.

Effectiveness of oxytetracycline in reducing the bacterial load in rohu fish(Labeo rohita,Hamilton)under laboratory culture condition

Objective:To observe the effectiveness of most widely used antibiotic,oxytetracycline(OTC)in reducing the bacterial load in rohu fish under artificial culture condition in the laboratory.Methods:The experiment was conducted in the Faculty Fisheries,Bangladesh Agricultural University,Mymensingh-2202.The fish were reared in 8 aquaria where fish in 5 aquaria were used for replication of the treatment(experimental group)and fish in remaining 3 aquaria were considered as a control(Control group).OTC was fed to the fish in the experimental aquarium at the rate of 2 g/kg through diet twice daily whereas fish reared under control condition was given feed without antibiotic for 20 d and bacterial content in the aquarium water,gills,skin and intestine of fish were estimated at every alternative day after onset of the experiment.Results:Rearing the fish with OTC treated feed resulted in gradual decrease of bacterial load in the aquarium water,gills,intestine and skin of the fish whereas the content remain unchanged Or little increased in the control group.W ater quality parameters such as dissolved oxygen,pH and total hardness were within the suitable range in the experimental aquarium but not in control aquaria throughout the experimental period.Conclusions:These results suggest that OTC could be a potential antibiotic to reduce the bacterial load in fish and can be used commercially for maintaining the fish health in aquarium conditions.

Molecular identification of oomycete species affecting aquaculture in Bangladesh

Fish mycotic disease outbreaks occur due to infections with oomycete pathogens such as Saprolegnia spp.and Aphanomyces invadans,and cause large-scale fish production losses.Despite its negative impact on aquaculture,little is known about the diversity of oomycete pathogens.The aim of this study was to identify the diversity of pathogenic oomycetes causing infections in major aquaculture zones of Mymensingh and Jessore regions in Bangladesh.A total of 449 water and infected fish samples were collected from 28 fish farms in both regions of which 29 samples were able to grow out with mycelia on the Potato Dextrose Agar(PDA)/Glucose Peptone Yeast Agar(GPYA)plates.Sequence database searches using the rRNA Internal Transcribed Spacer(ITS)region revealed that 15 belonged to Pythium spp.,12 were Aphanomyces invadans and two corresponded to Saprolegnia parasitica.Five isolates of Pythium spp.were identified to the species level:one was closely related to Pythium catenulatum,four to Pythium rhizo-oryzae,rest were identified up to genus.The Pythium spp.were only isolated from water samples whereas A.invadans and S.parasitica were found in fish lesions.Phylogenetic analysis revealed that a single A.invadans clone exists in the sampled area.The results obtained confirm the existence of pathogenic oomycetes in Bangladesh fish farms and this will pave future research on diversity,prevention and control measures.