Background: Biofloc technology relies on adding a carbon source to maintain optimal carbon to nitrogen ratio for transforming the waste into microbial biomass that aquatic animals can use. In the present study, the growth performance of the critically endangered Hypselobarbus pulchellus in biofloc-based seed rearing with different Carbon to Nitrogen ratio was studied.&nbsp; 
 
Methods: Healthy early fry (0.01 g) was randomly stocked into 15 circular FRP tanks (1000 L) at a density of 100 individuals/m3 and reared for 90 days. The carbon to nitrogen ratios of 5:1(CN5), 10:1(CN10), 15:1(CN15) and 20:1(CN20) were maintained using jaggery without considering carbon content derived from the feed and the control group received no additional source of carbon. 
 
Result: The results indicated that H. pulchellus had better growth performance in biofloc systems having higher C/N ratios. The highest weight gain (0.48&plusmn;0.01 g) and weight gain percentage (3931.15&plusmn;120.68%) and specific growth rate (4.11&plusmn;0.03% per day) were found in the CN10 group (P&lt;0.05), followed by CN15 and CN20, while the control group values were lowest. In terms of survival, all treatments had high survival rates ranging from 92% to 94.67%, with no significant variations (P&gt;0.05). The CN10, CN15 and CN20 treatments had significantly higher amylase, protease and lipase activities than control (P&lt;0.05). Moreover, the immunological and antioxidant activity increased with CN ratios. The CN10, CN15 and CN20 groups had significantly lower total ammonia nitrogen, nitrite and nitrate levels than control group (P&lt;0.05). Overall, this study suggests that C/N ratios of 10:1 to 20:1 are optimal for rearing H. pulchellus fingerlings from early fry, with 10:1 presenting the best growth results.

Growth Performance of Critically Endangered Hypselobarbus pulchellus in Biofloc Systems with Various C/N Ratios

<div>Background: Thamirabarani is a major east-flowing river originates from the Pothigai Hills of Southern Western Ghats (8&deg;36&#39;07.1&quot;N 77&deg;15&#39;50.9&quot;E) at an altitude of 2074 m with a catchment area of 5482 km2 and meanders through a distance of 120 km (24 km in hilly terrain and 96 km in plains) in Tirunelveli and Tuticorin districts and drains into the Bay of Bengal. Present paper provides information on abundance, distribution, human utility, Trophic level, Lm and IUCN status of the Thamirabarani River. 
 
Methods: The present study was conducted by monthly intervals on Ichythyofaunal diversity of the Potamon Zone of Thamirabarani River from November 2019 to October 2021, selecting seven sampling stations viz Cherenmahadevi, Vannarpettai, Murappanadu, Karungulam, Srivaikuntam, Eral and Authoor. 
 
Result: In the present study, a total of 57 species comprising 11 orders, 19 families and 38 genera were documented from downstream stretch of Thamirabarani River, of which three fish species namely Horadandia atukorali; Oreochromis mossambicus and Wallago attu are under vulnerable category and three fish species namely are Hypselobarbus dubius; Labeo fisheri and Dawkinsia tambraparniei endangered listed in the International Union for Conservation of Nature red list. Among the 11 orders reported, the order Cypriniformes (52%) was observed to have the highest contribution to the Ichthyofaunal diversity and the family Cyprinidae (32%) was recorded the highest contribution to the finfish diversity. The trophic level community structure of recorded fish species revealed the dominance of mid-level carnivores (48%). The human utility of recorded finfishes was found to be the highest was observed as edible (72%) and IUCN status was the highest with least concern (72%).</div>

Growth Performance of Critically Endangered Hypselobarbus pulchellus in Biofloc Systems with Various C/N Ratios

An Annotated Checklist of Ichthyofaunal Diversity of the Potamon Zone of Thamirabarani River, South India