Mystus Bleekeri Research Articles

Morphometric Characteristics, Length-Weight Relationships, and Condition Factors of Five Indigenous Fish Species from the River Ganga in Bihar, India

Morphometric characteristics, length-weight relationships (LWRs), and condition factors (K) were studied for five indigenous fish species belonging to five different families (Barilius barila Hamilton, Cirrhinus reba Hamilton, Chanda nama Hamilton, Mystus bleekeri Day, and Clupisoma garua Hamilton), from the River Ganga in Bihar, India. A total of 557 fish individuals were collected seasonally from September 2021 to August 2022 using a monofilament drift gill net and a conical trap net Khairel jal. In morphometric analysis, the highest degree of correlation was observed between the total length and the standard length for all species (except C. garua). The estimated exponent value b varies from 2.920 to 3.214, where the slopes of regression lines among the species have significant differences (p<0.0001). The b value indicated that three species (B. barila, C. nama, and C. garua) follow positive allometric growth, whereas M. bleekeri shows isometric growth and C. reba exhibits negative allometric growth. The condition factor value for these fishes ranged from 0.67 to 0.98, which indicated that the population of C. reba was robust compared to all other species (p<0.0001). A new maximum length (146.8 mm) was obtained for B. barila from India. The present study gives baseline biological information on five commercially important indigenous fish species found in the River Ganga, Bihar. As the population of these species has been dwindling in recent times, these data will be important for the conservation and sustainable utilization of these important species in the long run.

First report on length-weight relationships of commercially important fishes in potamon zone of the river Kosi, Supaul, Bihar, India

The length-weight relationships of five fishes: Mystus tengara, Mystus bleekeri, Ailia coila, Aspidoparia jaya, and Cabdio morar of Koshi River, Bihar, India, were estimated. The study is the first report on the LWR of these five species from Koshi River, Bihar. The relationships were calculated using the formula: Log W = Log a + b Log L and length-weight parameters (“a” and “b”), and coefficients of determination (r2) were determined. The regression coefficient (b) values are 2.51, 3.38, 1.93, 2.62, and 2.63 for Mystus tengara, Mystus bleekeri, Ailia coila, Aspidoparia jaya, and Cabdio morar specimens, respectively.

PROXIMATE AND MINERAL COMPOSITION OF FOUR TENGRA (MYSTUS SP.) FISHES OF BANGLADESH

Body flesh of the four fish species (Mystus) namely Mystus gulio, Mystus bleekeri, Mystus cavasius, and Mystus vittatus were collected and proximate composition and mineral contents (Na, K, Ca, Mg, P, Fe, Zn and Cu) were analyzed. The highest amount of protein (22.2±0.94%) and lipid (5.25±0.64%) were found in M. gulio. The maximum moisture (79.31±1.86%) and ash content (1.45±0.14%) were observed in M. cavasius where the M. gulio showed the lowest moisture content (71.5±0.95 %) and M. vittatus showed the lowest ash content (1.03±0.06%).The concentration range of Ca, Na, K, Mg, and P were 128±5.09 mg to 288± 2.94 mg, 67.2±0.8 to 86±2.16 mg, 254.5±2.43 to 316.8±3.98 mg, 43.0±1.31 to 47.4±1.31 mg and 122.5±1.89 to 220±1.8 mg per 100 g fish flesh respectively. M. gulio showed the highest amount of Na (86±2.16 mg) and P (220±1.8 mg). Among four species of Mystus fish, M. cavasius had the highest amount of Ca (288±2.94 mg) while M. vittatus showed the highest amount of both K (316.8±3.98 mg) and Mg (47.40±1.31 mg). Micro mineral contents in different Mystus species were more or less similar except the M. bleekeri, which showed a higher concentration of Fe (5.47±0.56 mg) where as M. cavasius contained no Cu.

Studies on blood volume in a teleostean fish, Mystus bleekeri in relation to body weight in summer and winter seasons

The total blood volume, relative (%) blood volume and haematocrit value of Mystus bleekeri of six different weight groups ranging from 24 to 76 grams were studied in winter and summer months at water temperatures of 18°C and 28°C. The total blood volume at both temperatures increased from lower to higher weight groups. The correlation coefficient between total blood volume and body weight were 0.8587 at 18°C and 0.9946 at 28°C. Total blood volume in all weight groups was greater at the higher temperatures and most results were statistically significant. The relative blood volume and haematocrit decreased from lower to higher groups at both temperatures.

EFFECT OF STOCKING DENSITY ON GROWTH AND SURVIVAL OF ENDANGERED MYSTUS BLEEKERI (DAY, 1877) IN NURSERY SYSTEM

The effect of stocking densities on growth, survival and production of gulsa tengra, Mystus bleekeri fry and fingerlings were practiced in a nursery rearing system. The experiment was designed with 3 treatments and 3 replications and conducted for seven weeks in nine earthen nursery ponds of 0.032 ha each. Four-days-old hatchlings were stocked at 0.60 million/ha, 0.80 million/ha and 1.0 million/ha was designated as treatment T, T and T. At stocking, hatchlings 1 2 3 had a mean length and weight of 0.91±0.01 cm and 0.001±0.01g. Hatchlings in all treatments were fed with 32.90% crude protein and 8.80% crude lipid. Physico-chemical parameters (temperature, transparency, pH, dissolved oxygen and total alkalinity) and plankton populations were at the optimum level for fish culture. The highest weight gain (3.16±0.66g) was measured in treatment T and the lowest (2.01±0.88 g) in treatment T Final length, final weight and survival 1 3. of fingerlings followed the similar trends as weight gain. Specific growth rate and feed conversion ratio was significantly better (P<0.05) in treatment T followed by treatment T and T Survival 1 2 3. rate was also higher (P<0.05) in treatment T than in treatment T and T, respectively. Despite 1 2 3 this, higher economic returns (Bd Tk. 367733/ ha) were observed for treatment T than from 1 treatment T and T.

Biological and Reproductive Indices of Mystus bleekeri (Day, 1877) in Open Water Body (Dekhar Haor) of Bangladesh

Some biological and reproductive aspects of the Mystus bleekeri from Dekhar Haor were investigated. From the commercial catches, a total of 600 sample collections were performed on a monthly basis from July 2017 to June 2018. Total length (TL, cm), body weight (W, g) and individual’s sex were identified between 216 male (36%) and 384 female (64%) fish (ratio 1.00: 1.78). Mean TL and W of samples were 14.85±3.38 cm and 27.54±15.76 g, respectively. The TL of male and female ranged from 6.9-21.3 and 7.80-24.60 cm, respectively; and W ranged from 5.3-63.3 and 6.70-76.40 g, respectively. In length–weight relationship of this fish depicted a negative allometric growth (b=2.408) with a condition factor (Kn) of 1.04±0.11. Fish of 16.00-16.90 and 10.00-10.90 cm length groups demonstrated the highest (1.45±0.23) and lowest (0.89±0.18) Kn values, respectively which was significantly varied among different length groups. Monthly study of gonadosomatic index showed two peaks in the month of May-June and November for both sexes. The results of this study provide baseline data on some biological aspects of M. bleekeri, which would be useful in predicting the responses of M. bleekeri populations in Dekhar Haor. 

Seasonal Dynamics of Stomach Contents, Trophic Level, Length-Weight Relationship and Condition Factor of Mystus bleekeri (Day, 1877)

The Asian catfish Mystus bleekeri is a popular food fish along with favored as an ornamental fish in Bangladesh. Till now detailed report on stomach contents, trophic level, length-weight relationship and condition factor of this fish species in the agro-climatic context of Bangladesh is lacking. Hence, the aims of this study were to describe the stomach content, trophic level, length-weight relationship (LWR) and condition factors of Mystus bleekeri collected from Dekhar Haor, Sylhet, Bangladesh from July 2017 to June 2018. A total of 600 specimens ranging from 6.9-24.6 cm total length (TL) and 5.7-72.4 g body weight (BW) was analyzed in this study. Stomach content analysis showed that the fish fed mostly on Mollusca with a frequency of occurrence (fo: 25.36%) and worms (fo: 21.68%), followed by plant matters (fo: 3.32%), Cladocerana (fo: 1.18%), Copepoda (fo: 0.95%), and Teleostei (fo: 0.36%). The estimated mean trophic level (TROPH) ranged from 2.35±0.13 in December to 3.02±0.23 in August, indicating that they are opportunistic feeder. The LWR analysis showed negative allometric growth (b<3) throughout the year. The values of the exponent b in the LWR (W=aLb) vary between 1.474 and 2.490.The mean K value was significantly higher in October indicating the heavier weight and better condition of the fish (P<0.05). The data obtained from this study would be useful to introduce sustainable management of Mystus bleekeri not only in Dekhar Haor but also in other inland waters of Bangladesh.

Nutritional Analysis and Overall Diet Quality of Fresh and Sun-dried Mystus bleekeri

Background: Mystus bleekeri (M. bleekeri) is a small, freshwater catfish, with a maximum length of 15.5cm, which belongs to family Bagridae and order Siluriformes. It can be consumed both in fresh and processed form. Sun-drying is one of the most important traditional methods for processing M. bleekeri. However, neither fresh nor sun-dried M. bleekeri is normally consumed in raw form. Various cooking methods are applied to prepare them. Objective: The objective of the present study is to estimate the nutritional values of fresh and sundried Mystus bleekeri and evaluate the effect of different cooking methods on their nutrient contents. Methods: Proximate Analysis of minerals, amino acids, and fatty acids was performed using sophisticated analytical instruments. Results: Changes in various micronutrients and macronutrients were observed in the present study. The total amount of fat and ash content was found to be higher after frying in a fresh sample of M. bleekeri. Mineral content was found to be higher in sun-dried fish whereas that was reduced after boiling. Aspartic acid was the major component of fish protein. Saturated fatty acids were the most abundant in both fresh and sun-dried M. bleekeri which were increased through frying. Conclusion: The present experiment showed that after frying, minerals and fatty acids content exhibited higher concentration in both fresh and sun-dried M. bleekeri which is good for human health.

Trace Metals Contamination in Riverine Captured Fish and Prawn of Bangladesh and Associated Health Risk

Trace metals contamination is ubiquitous in the riverine environments of Bangladesh. Trace metals contamination is increasing rapidly in Dhaleshwari River due to rapid urbanization and industrialization along the riverbank, especially after the establishment of the Tannery Industrial Estate at Savar in Dhaka District. As a result, aquatic ecosystems, including fish and prawn species of the river, are contaminated by various trace and toxic metals. We examined the concentrations of 10 trace metals (Cr, Fe, Zn, Mn, Co, Ni, Cu, As, Hg, and Pb) in 20 different fish and prawn species (n = 41) which are commonly found in the Dhaleshwari River using energy-dispersive X-ray fluorescence (EDXRF) method. The potential human health risks (noncarcinogenic and carcinogenic) of the trace metals were calculated by using Target Hazard Quotient (THQ), Hazard Index (HI), and Target Cancer Risk (TR) indices. The mean concentration (mg/kg; ww) of the trace metals in analyzed riverine fish and prawn species was in the order of Fe > Zn > Cu > Cr > Mn > Co > Hg > Ni > Pb > As. The highest concentration of Fe (74.67 mg/kg) and Cr (4.64 mg/kg) was found in Mystus bleekeri, whereas Zn (38.89 mg/kg) and Cu (17.47 mg/kg) were found in Rohtee cotio and Glossogobius guiris, respectively. The target hazard quotient (THQ) values were less than 1 (no detrimental health effects) for all the specific metals in most of the species except M. bleekeri (1.61), G. guiris (1.29), Corica soborna (1.28) for Cr, and Macrobrachium malcolmsonii (1.19) for Hg indicate that the noncarcinogenic health risk to humans by consuming those species was relatively low. However, nine out of twenty species found higher Hazard Index (HI) values than the recommended value (HI = 1), indicating that regular consumption of these fishes may have considerable harmful effects on human health. The highest HI value (2.85) was found in M. bleekeri. Moreover, target cancer risk (TR) values showed that frequent intake of some species for prolonged periods might pose a carcinogenic risk due to Cr and Ni contamination as they were higher than the maximum accepted value of 10−4. Based on the present study, it is imperative to take an urgent initiative to control or prevent the trace metals contamination in the Dhaleshwari River and minimize the human health risks associated with the consumption of fish and prawn species in this river in Bangladesh.

Comparative performances of exotic and indigenous fish species with commercial culture systems of Mymensingh district in Bangladesh

An experiment was conducted to assess the relative performances of indigenous and exotic fish species under commercial culture system at Muktagacha and Trishal upazila in Mymensingh district. Six exotic fish species namely Thai koi (Anabas testudineus), Thai pangus (Pangusius hypophthalmus), Silver carp (Hypophthalmichthys molitrix), Vietnam koi (Anabas testudineus), Big head carp (Aristichthys nobilis) and Tilapia (Oreochromis niloticus) and nine indigenous fish species namely Rui (Labeo rohita), Shing (Heteropneustes fossilis), Sar punti (Puntius sarana), Gulsha (Mystus bleekeri), Koi (Anabas testudineus), Mrigal (Cirrhinus cirrhosus), Kalibaush (Labeo calbasu), Catla (Catla catla) and Magur (Clarias batrachus) were selected in Muktagacha while exotic Big head carp and indigenous Gulsha, Koi and Magur were lacking for observation in Trishal upazila. Results revealed that the production of exotic Thai pangus was comparatively higher in Muktagacha (5810.81 kg/acre) than Trishal (4521.74 kg/acre) upazila. In contrast, silver carp and tilapia production were 3063.04 kg/acre and 1008.26 kg/acre in Trishal, respectively which were higher than Muktagacha. Average selling price of tilapia, Vietnam koi and silver carp was also comparatively higher in Muktagacha than Trishal upazila. Similar observation was also obtained in respect of indigenous fish species. On the other hand, average selling price of shing was found highest (BDT. 333.33 per kg) in Muktagacha than Trishal while other fish species were sold at similar price. Gross income was also significantly higher with the exotic fishes in Muktagacha accounted for BDT. 858,716/acre/cycle while the highest gross income obtained with the indigenous fishes was in Trishal upazila, valued BDT. 121,5987/acre/cycle. It can be concluded that, both indigenous and exotic fish farming has spread in the area because of easy to adopt culture system, availability of fry, feed, good profit and high demand in the market. Some limitations of the ongoing practices have been identified that need to be addressed properly by the concerned authority.
 Progressive Agriculture 29 (4): 371-379, 2018

Prevalence and Intensity of Cornudiscoides Agarwali (Monogenoidea) on the Gills of Day's Mystus (Mystus Bleekeri) in Relation to Some Ecological and Biological Factors from Arunachal Pradesh, India.

SummaryThis work investigated the relationship of host size, seasons, and water quality parameters with the prevalence and intensity of Cornudiscoides agarwali on Mystus bleekeri collected from the Dikrong River in Arunachal Pradesh, India from February 2016 to January 2017. A total of 2760 specimens of C. agarwali were recovered from 114 individuals of M. bleekeri. The levels of mean intensity, but not the prevalence, of infection of C. agarwali were positively correlated with fish host size, peaking in the largest size class (45.20 ± 5.69 parasites/fi sh). The prevalence values had a statistically significant seasonal trend, reaching highest (100 %) during the pre-monsoon season, followed by 91.8% during the post-monsoon period and 87.5 % during the monsoon season. The levels of mean intensity of infection were also dependent on the seasons, reaching significantly higher levels during the pre-monsoon season (42.75 ± 4.18 parasites/fi sh). All water quality parameters measured were within the safety value recommended for freshwater aquaculture. Cornudiscoides agarwali maintained its prevalence above 87.5 % throughout the annual cycle, which means it was able to reproduce year-round in a non-polluted river. This could be an indication of monogenoidean community and population dynamics thriving best under optimum water quality parameters. Also, this article draws the attention of parasitologists and ichthyologists to a taxonomic problem of the misidentification of Mystus spp., and therefore, possibly of their parasitic monogenoids.

The first record of two trichodinid ectoparasites, Trichodina pseudoheterodentata Tang et al. 2017 and Trichodina hafizuddini Asmat, 2005 (Ciliophora: Peritricha) from the freshwater fishes in the Baikka Beel of Moulvibazar district in Sylhet division, Bangladesh

A parasitological investigation on trichodinid ciliates from several freshwater fishes in the Baikka Beel of Moulvibazar district of Sylhet was carried out between January and December 2015. During the investigation period, two parasitic trichodinid ciliates (Ciliophora: Peritrichia), Trichodina pseudoheterodentata Tang et al. 2017 and Trichodina hafizuddini Asmat, 2005 were morphologically studied and described with using the silver nitrate impregnation technique. Trichodina pseudoheterodentata was isolated from the gills of Mystus bleekeri, while Trichodina hafizuddini from the gills of Amblypharyngodon mola. This investigation has been revealed that these two Trichodina species fall within the range of morphometry and agree closely in the overall appearance of the adhesive disc with the original populations. Geographical variation was also observed by considering the body size and number of the denticles. Depending on country’s available taxonomical survey on trichodinid ciliates, this study is the first formal report on these trichodinids from any part of Bangladesh.

New maximum size records and length-weight relationships for two species, Corica soborna (Hamilton, 1822) and Mystus bleekeri (Day, 1877), from the Ganges River (NW Bangladesh)

This study records new maximum lengths and provides length–weight relationships (LWRs) for two small indigenous fishes, Corica soborna (Hamilton, 1822) and Mystus bleekeri (Day, 1877), from the Ganges River in northwestern Bangladesh. Fishes were sampled sporadically using gill nets and cast nets from August 2015 to July 2016. New maximum recorded lengths weere 5.3 cm total length (TL) for C. soborna and 17.7 cm TL for M. bleekeri. The LWRs were highly significant (p < .001) with r2 values >.958. These findings will play a significant role in the fisheries resource management.

Studies on Fish Diversity and Need for Their Conservation of Singhiya River, Morang District, Eastern Nepal

In the present study, twenty six species of fishes were recorded from Singhiya river, Morang district, Nepal during January to August (2016). The population present status of important fish species such as Gagata cenia and Lepidocephalus guntea was found to be threatened. Macrognathus pancalus and Mystus bleekeri was to be vulnerable and Glossogobius giuris and Puntius sarana to be intermediate. The Singhiya river have been found to be influenced by harmful human activities such as deforestation, direct waste disposal, discharge of toxic substances-fertilizers, pesticides through surface run-off from the agricultural field near the river and urbanization, industrialization, use of soaps and detergents, indiscriminate fishing, pollution, waste dumping are destroying the fresh water habitat and have been found to threaten the natural environment of fish diversity of Singhiya river which ultimately lead to their extinction and must be stopped or managed in a proper way for the conservation and sustainable utilization of aquatic-bioresources of the river.

Length-weight and length-length relationships of fiveMystusspecies from the Ganges and Rupsha rivers, Bangladesh

This study focused on the length–weight and length–length relationships of five Mystus species from Bangladesh. A sum of 398 individuals (Mystus bleekeri = 47, Mystus cavasius = 171, Mystus gulio = 59, Mystus tengra = 65, and Mystus vittatus = 56) was collected from the Ganges and Rupsha rivers, Bangladesh. Fishes were caught by gill net (mesh sizes: 2.0–4.0 cm) and cast net (mesh sizes: 1.5–3.0 cm) from July 2014 to June 2015. Total length (TL), fork length (FL) and standard length (SL) were measured to 0.1 cm, while whole body weight (W) was taken to the nearest 0.1 g for each individual. The TL ranged from 6.0–13.5 cm for M. bleekeri, 5.0–15.0 cm for M. cavasius, 7.4–17.2 cm for M. gulio, 4.6–11.6 cm for M. tengra and 5.5–12.3 cm for M. vittatus. The W varied from 3.0–18.2 g for M. bleekeri, 1.3–30.4 g for M. cavasius, 6.1–62.2 g for M. gulio, 1.7–15.1 g for M. tengra and 2.7–19.2 g for M. vittatus. All LWRs were highly significant (p < .001), with all r2 values ≥.950. The LLRs were also highly significant (p < .001), with all r2 ≥.980. This study provides information on LWRs and LLRs for M. gulio and M. tengra for the first time. The results of this study can be very effective for stock assessment of Mystus species in the Ganges and Rupsha rivers as well as in the surrounding ecosystems.

Some deformed specimens of Mystus bleekeri (Day) and Labeo bata (Ham. Buch) from the river Chenab in Pargwal wetland, Akhnoor, Jammu

Four adult deformed specimens of Mystus bleekeri showing caudal fin deformities viz complete degenerated caudal fin, degenerated upper caudal fin lobe, degenerated lower caudal fin lobe and truncated caudal peduncle and bulbous caudal fin base and one specimen of Labeo bata with a blunt head and terminal mouth were observedamong the fish collections from the river Chenab in Pragwal wetland area and have been described. Deformities in M. bleekeri are most probably caused by Myxobolus infection and in L. bata it is the result of injury.

Deposition of chromium in aquatic ecosystem from effluents of handloom textile industries in Ranaghat–Fulia region of West Bengal, India

Accumulation of chromium (Cr) was determined in water, sediment, aquatic plants, invertebrates and fish in aquatic ecosystems receiving effluents from handloom textile industries in Ranaghat–Fulia region of West Bengal in India. Cr was determined in the samples by atomic absorption spectrophotometer and data were analyzed functionally by Genetic Algorithm to determine trend of depositions of Cr in the sediment and water. Area plot curve was used to represent accumulation of Cr in biota. The results indicate that the aquatic ecosystems receiving the effluents from handloom textile factories are heavily contaminated by Cr. The contamination is hardly reflected in the concentration of Cr in water, but sediment exhibits seasonal fluctuation in deposition of Cr, concentration reaching to as high as 451.0μgg−1 during the peak production period. There is a clear trend of gradual increase in the deposition of Cr in the sediment. Aquatic weed, insect and mollusk specimens collected from both closed water bodies (S1 & S2) and riverine resources (S3 & S4) showed high rate of accumulation of Cr. Maximum concentration of Cr was detected in roots of aquatic weeds (877.5μgg−1). Fish specimens collected from the polluted sites (S3 & S4) of river Churni showed moderate to high concentration of Cr in different tissues. Maximum concentration was detected in the liver of Glossogobius giuris (679.7μgg−1) during monsoon followed by gill of Mystus bleekeri (190.0μgg−1) and gut of G. giuris (123.7μgg−1) during summer. Eutropiichthys vacha showed moderately high concentration of Cr in different tissues (65–99μgg−1) while Puntius sarana showed relatively low concentration of Cr (below detection limit to 18.0μgg−1) in different tissues except in gill (64.4μgg−1).

Fish diversity of Indus river at Beka Swabi, Khyber Pakhtunkhwa, Pakistan

The Present study deals with fish diversity of Indus River at Beka Swabi. The main aim of this study is to know whether this area of Indus river is rich in fish fauna or not. Present study was conducted for four months that was from November 2012 to February 2013. In this duration 14 species were reported, in which, 04 species were reported in November, 02 species were reported in December, 02 species were reported in January and 06 species were reported in February. These 14 species belong to 05 orders, 05 families, and 11 genera. Orders were Cypriniformes, Siluriformes, Beloniformes, Mastecembeliformes and Channiformes. Families were Cyprinidea, Bagridae, Belonidae, Mestacembelidae and Channidae. Genera were Rasbora, Cyprinus, Labeo, Catla, Tor, Channa, Mystus, Ompok, Xenentedon and Mastacembelus. Species were Rasbora daniconius, Cyprinus carpio, Carassius auratus, Labeo rohita, Catla catla, Tor putitora, Channa punctatus, Channa gachua, Mystus vittatus, Mystus bleekeri,Ompok pabda, Xenentedon cancila and Mastacembelus armatus. According to this survey of fish diversity of Indus River at Beka Swabi, the family Cyprinidea was richest family which consists of 07 species, while second richest family was Bagridae which consist of 03 species, third richest family was family Channidae which consist of 02 species and remaining each family consist of single species. It’s also concluded from such study that present area of Indus river is rich in fish fauna.

Length-weight and length-length relationships of freshwater wild catfish Mystus bleekeri from Nala Daik, Sialkot, Pakistan

Length-weight (LWR) and length-length relationships (LLR) were determined for a freshwater catfish Mystus bleekeri (Day, 1877) collected from Nala Daik, Sialkot, Pakistan. A total of 105 specimens (56 males; 49 females) were collected from February to March, 2010. Each specimen was weighed (g) and measured (cm). The total length of specimens studied ranged from 5.5 to 7.8 cm. Linear regression analysis was used, first to compute the degree of relationship between length and weight and then among total (TL), standard (SL) and fork lengths (FL). LWR exhibited a highly significant correlation (P < 0.001). The overall value of the exponent of LWR (b = 2.62) suggested negative allometric growth. Results for LLRs indicated that these are highly correlated (P < 0.001). Furthermore, the first reference for separate male, female and combined sex of length-weight and length-length relationships for Mystus bleekeri was provided. Key words : Mystus bleekeri , length-weight relationship, length-length relationship, predictive equations.

Effects of animated images of sympatric predators and abstract shapes on fear responses in zebrafish

Previously, zebrafish were shown to respond to the presence of a live predator, the sight of a live predator, moving computer images of a predator, and images of different moving objects in a context and stimulus specific manner. For example, zebrafish showed a robust antipredatory reaction towards a sympatric predator, the Indian leaf fish (Nandus nandus) but not towards an allopatric predator or sympatric or allopatric harmless fish species. In a subsequent study, however, we found zebrafish not to show avoidance in response to the image of another sympatric predator, Xenentodon cancila. The results implied that zebrafish may possess genetic predispositions that allow them to effectively evade at least certain sympatric predators without any prior exposure to them. However, it is not known whether zebrafish can respond to other sympatric predators with antipredatory reactions without any prior exposure to such predators. It is also not known whether such responses may be dependent upon, or idiosyncratic to, predator species. To answer these questions, we examined the effect of computer animated (moving) images of five different predator species all sympatric with zebrafish (Nandus nandus, Channa maculata, Xenentodon cancila, Mystus bleekeri, Chitala chitala) and of two abstract shapes (star and rectangle, also animated) on zebrafish behaviour. The results confirmed that the sight of N. nandus is an aversive stimulus and that the image of X. cancila is not. However, the results also revealed that images of three other species (C. maculata, M. bleekeri, C. chitala) and that of a rectangle induce even more robust aversive reactions than what is elicited by N. nandus. At this point we do not know what features of the images may be perceived as aversive by zebrafish or whether the observed behavioural responses would be adaptive or effective in nature. Nevertheless, we argue that image-presentation based fear paradigms will be useful in future translational research. We also conclude that it may be premature to decide whether zebrafish can recognize their sympatric predators.