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A ninety days experiment was carried-out to evaluate the effect of dietary replacement of fishmeal (FM) (locally available dried non-defatted Coilia dussumieri V.) by graded inclusion levels of non-defatted non-mulberry Indian tropical tasar silkworm spent pupae (Antheraea mylitta D.) on growth performance, feed consumption, digestive enzyme response, body chemical composition, and intestinal cellular micro-morphological status of the reared striped catfish (Pangasianodon hypophthalmus S.). Five iso-nitrogenous (280 g protein kg-1) and iso-energic (19 MJ kg-1) extruded floating feeds were formulated by gradually replacing the FM with NDSWP (non-defatted silkworm pupae) at 0%, 25%, 50%, 75%, and 100% (on protein to protein basis) levels and the diets are designated as NDSWP0, NDSWP25, NDSWP50, NDSWP75, and NDSWP100, respectively. The contribution of calculated pupae crude protein was 0%, 4.75%, 9.50%, 14.25%, and 19% out of the total protein (28%) content in the respective diets. The experiment was executed in the floating net-cage located at the Maithon reservoir, India which is a field research station of ICAR-CIFRI, Barrackpore, Kolkata, India. The designated diets were randomly allocated to 10 numbers of experimental cages (each 5 ×5 ×3 m), in triplicates stocked with 2475 numbers (stocking density at 33 numbers per m3) of striped catfish in each replication and fed daily twice at 08.00 h and 16.00 h. The initial stocking size of the striped catfish fingerling was 16.56 ± 0.08 g. At the termination of the feeding experiment, the final body weight (g), individual weight gain (g), weight gained (%), feed conversion ratio (FCR), specific growth rate (SGR), and protein efficiency ratio (PER) found to be non-significantly different (p < 0.05) up to 50% protein replacement level (NDSWP50) in comparison to the control (NDSWP0). Among the biological indices, hepatosomatic index (HSI) exhibited a non-significant difference stretching to NDSWP50 treatment group with a distinct significant difference between NDSWP25 and NDSWP100 (p < 0.05), when, an inverse trend was recorded in relation to increasing pupae meal in the diets. Among the digestive enzymes, relatively higher protease enzyme activity was observed in the diet fed at NDSWP50 compared to the rest of the treatment groups, although, it was statistically non-significant (p > 0.05). Amylase and lipase enzyme activities recorded a significant difference among the treatment groups (p < 0.05). A higher amount of fish muscle crude protein was noticed in the NDSWP50 treated group than in the rest of the treatment groups. The lipid content of fish muscle indicated its higher content over the initial and exhibited an inverse relationship with moisture and ash content at the end of the experiment. Histo-morphology of gut tissue confirms the suitability of feeding pupae protein incorporated diet with the gradual replacement of fishmeal protein. The findings of the current feeding trial suggests that the inclusion of non-defatted non-mulberry silkworm pupae protein at 50% level of fishmeal protein substitution without compromising the growth performance, nutrient utilization, conversion of feed, and other biological indices, and economics of diet. • Indian tropical tasar (Antheraea mylitta) is a non-mulberry silkworm pupae, a sericultural bio-waste rich in nutrients. • It is achievable to replace 50% fishmeal protein in striped catfish (Pangasianodon hypophthalmus) diet with tasar silkworm pupae protein without compromising growth-nutritional accountability. • The gut micro-morphology reveals a sign of inflammation in lamina propria region in fishes fed with greater than 50% pupae protein containing diet. • Economic analysis evident 35% trimming in feed cost. [ABSTRACT FROM AUTHOR]