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The Hilsa, Tenualosa ilisha, commands a very high value as food fish. The present study was carried out to understand the breeding phenology of T. ilisha in relation to climatic variables. Monthly fish samples were collected from two landing centres, namely, Uzanbazar (Guwahati) and Shri Ramghat, Dhubri, of River Brahmaputra during May 2018 to April 2019. The assessment of gonadosomatic index (GSI) of T. ilisha revealed higher GSI values during October to February, and showed temporal variations with respect to sex. In males, highest GSI value was observed in the month January followed by February, whereas in females, GSI value was found to be highest in November followed by October. GSI (pooled) value was negatively correlated with air temperature, indicating vulnerability of the species to climate change. The highest percentage of mature males was observed during October–February, and mature females during October–December. The length at first maturity was recorded to be 290 mm for female(s) and 259 mm for male(s). The absolute fecundity ranged from 103,164 to 583,456 ova for fishes in the size range of 229–403 mm, with an average of 250,532 ova per female. Relative fecundity was found to range from 306 to 1096 ova per gram body weight, with an average of 791 ova per gram body weight. The diameter of ova of the studied fishes ranged from 414.6 to 738.2 µm, with a mean value of 546.73 ± 7.18 µm. The percentage frequency distribution of mature ova shows a distinct single peak or mode. Sex ratio (male: female) was found to be 1:0.87, indicating dominance of males over females. The chi-square test on observed sex ratio against the hypothetical ratio of 1:1 did not reveal a significant difference (p > 0.05). The findings of the present study can provide impetus toward successful management of this highly prized, transboundary, and migratory resource of River Brahmaputra, in the context of changing climate.

India is blessed with vast floodplain wetland resources of 0.5 million ha that are distributed in the Eastern and North Eastern States. They possess varying morphometry, ecological profile, trophic...

Indian minor carp Labeo bata fingerlings were reared in square shaped cages at different numbers to evaluate the effect of stocking density on growth, production and economics. Fifteen cages (5 × 5 × 2 m each) were installed in deeper areas (6–8 m) of Samaguri beel (a seasonally-flooded floodplain wetland) of Assam, India. The cages were stocked with L. bata (mean length 11.93 ± 0.20 cm; mean weight 13.05 ± 0.77 g) at five different stocking densities of 10 (SD10), 20 (SD20), 30 (SD30), 40 (SD40) and 50 (SD50) fingerlings m−3 in triplicates. Fish were fed with floating pellets containing 32% CP at 3–5% body weight twice-a-day for six months. Density-dependent growth was evident from the results as growth of fish decreased with increasing stocking densities; the specific growth rate of the fish at SD10, SD20, SD30, SD40 and SD50 were 1.03 ± 0.02, 0.88 ± 0.01, 0.84 ± 0.02, 0.67 ± 0.02 and 0.52 ± 0.01 with corresponding weight gain percent of 533.3 ± 13.41, 385.8 ± 10.73, 353.3 ± 14.17, 232.2 ± 8.08 and 155.9 ± 5.38, respectively. However, the highest net yield of fish was achieved at SD30 (50.8 kg cage−1), which was significantly higher than other stocking densities. Also, economic analysis demonstrated highest benefit-cost (B:C) ratio at 30 fish m−3 (1.44). Results indicated decreased fish yield at lower densities though the individual growth rate of fish was higher. On the other hand, fingerling stocking more than 30 fish m−3 was uneconomical because of lower individual growth rate. Hence, a stocking density of 30 fish m−3 could be considered as optimum for production of L. bata table fish in cages. The study generated new and critical information on species diversification in cage aquaculture for tropical floodplain wetlands.

Length–weight relationships for six small indigenous fish species, namely: Trichogaster chuna (Hamilton, 1822), Trichogaster lalius (Hamilton, 1822), Trichogaster fasciata Bloch & Schneider, 1801, Chanda nama Hamilton, 1822, Parambassis lala (Hamilton, 1822), and Macrognathus aral (Bloch & Schneider, 1801) were studied for the first time from Deepor beel, a Ramsar site (589 ha water spread area) located in Assam, India. A total of 617 fish specimens were collected for the present study on a monthly basis from February to August in 2016 from landing centres adjoining the beel. In the present study, b value ranges from 2.778 to 3.215, which is within the normal range. The LWRs for these six fish species from Deepor beel had not yet been reported for FishBase.

An experiment was carried out to evaluate the growth performance and yield of Labeo bata reared in cages at different stocking densities in a floodplain wetland of Assam, India. Fifteen cages (effective water volume 40 m3 each) installed in the wetland were stocked with fingerlings of L. bata (mean length 8.20 ± 0.08 cm; mean weight 4.82 ± 0.13 g) at five different stocking densities, i.e., 25 (D25), 50 (D50), 75 (D75), 100 (D100) and 150 fingerlings m−3 (D150) in triplicates. Fish were fed with pelleted feed containing 30 % CP at 3–5 % body weight twice-a-day for six months. Specific growth rate of the reared fish recorded at different stocking densities were 1.08 ± 0.03, 0.89 ± 0.01, 0.90 ± 0.05, 0.77 ± 0.02 and 0.57 ± 0.02 % day-1, respectively, in D25, D50, D75, D100 and D150. The corresponding weight gain percent were 604.77 ± 35.63, 395.37 ± 11.32, 407.88 ± 44.91, 296.61 ± 13.07 and 180.70 ± 11.02. In general, growth performance of the reared fish was inversely proportional to stocking density. However, yield (biomass) increased with increase in stocking density of up to 75 fingerlings m-3 after which no significant increase was observed. Economics of the cage aquaculture system also showed highest net revenue and benefit-cost ratio at 75 fingerlings m-3. Rearing of fish at this stocking density yielded 50 % higher fish production and generated 92.5 % higher net revenue than rearing at the lowest stocking density. The results suggest 75 fingerlings m-3 as the optimum stocking density for rearing L. bata in net cages.

The present study investigated traditional fishing devices namely Bundh, Dori and Gori Jal operated by fishers of Cachar District, Assam in rivers and small canals. The study was carried out in Ghagra River and adjoining small canals. Water current as well as indigenous knowledge of fishers on movement of fishes and foraging behaviour of freshwater prawns were found to be utilised to a great extent to catch the target species. Assessment of the effectiveness and rationality as perceived by fishers and experts respectively showed that Bundh fishing was highly effective Mean Perceived Effectiveness Index (MPEI score >2.5) whereas the other two fishing techniques namely Dori and Gori Jal were effective (MPEI score >2). All the three indigenous fishing techniques were found to be rational with a mean score ≥3.

Tenualosa ilisha, commonly called Hilsa, is a highly prized species, which has declined in River Brahmaputra, India. The study was carried out for one year and a total of 1,026 individuals were sampled at monthly intervals. In the study, the following growth parameters were observed: asymptotic length (L∞) = 445 mm, growth coefficient (K) = 0.5 year-1, and age at length zero (t0) = −0.5 year-1. Growth performance index (φ) was estimated to be 2.996. Natural mortality rate, total mortality, and fishing mortality was found to be 0.51 year-1, 1.57 year-1, and 1.06 year-1,respectively. Exploitation ratio (E) was found to be 0.675, which indicates that the species is slightly over-exploited. It was seen that length groups that represented the catch in the Indian part of River Brahmaputra comprised fishes of 0–4+ years age. The present study was carried out to assess the population characteristics of this commercially important species from the Indian part of Brahmaputra River, which will contribute towards sustainable fisheries management.