Search

The growth and sustainability of freshwater aquaculture are highly dependent on economic feed which is the major running cost. Fish feed industries depend on the high-priced fish meal (FM) as protein source in feed formulations. In this context, a nutrient-rich, and palatable insect meal-based fish feed was developed incorporating the black soldier fly (BSF) (Hermetia illucens) prepupae meal (BSFPM) reared on organic waste imparting additional benefit of waste bioremediation to make cost-effective feed. Feeding trial was conducted to evaluate growth performance on monosex Nile tilapia (Oreochromis niloticus). The different treatments were (1) dried BSF prepupae, (2) BSF prepupae and BSFPM-based feed in 1:1 proportion, (3) BSFPM feed, and (4) control feed with FM. The survival, growth, feed efficiency, and haematological parameters were not significantly different between BSFPM and control feed. Fish fed with control feed and BSFPM feed showed significantly higher (P ≤ 0.05) weight gain, specific growth rate, and percentage weight gain. Lowest food conversion ratio (P ≤ 0.05) was recorded for fish fed control feed with a significantly higher feed efficiency ratio (0.65

Reservoirs are aquatic resources with the potential to increase India's fish production through inland fisheries. Thippagondanahalli is a medium-size reservoir on Arkavathy River, a tributary of the Cauvery. It is located in Bangalore rural district of Karnataka (12°58’24” to 12°96'49" N 77°20’33” to 77°35’63” E) and has a water surface area of 1162 ha at full reservoir level and 784.55 m at full supply level. Fish diversity studies were conducted to examine the spatial and temporal variations in fish diversity in relation to habitat parameters. A taxonomic abundance of 25 fish species (80% of them native) belonging to 14 families and 4 orders was recorded. A range of statistical estimators such as Chao 1, Jack 1, and Bootstrap were used to assess the expected species richness. The Jack 1 method showed the highest abundance with 28 species. The littoral zone, dominated by small indigenous species, was found to have relatively higher fish diversity (Shannon index-1.86) compared to the limnetic zone of the reservoir. Shannon diversity was higher in the monsoon season (1.76) compared to other seasons. Physico-chemical parameters revealed that this waterbody is highly eutrophic. Canonical correspondence analysis between seasonal habitat characteristics and seasonal species abundance showed the abundance of the small indigenous fish Amblypharyngodon mola during the post-monsoon season, the bottom feeder Cirrhinus mrigala and the surface feeder Rasbora daniconius during the monsoon season, and the carnivores Mystus malabaricus and Channa orientalis as well as the planktivore Puntius sarana during the pre-monsoon season. This study suggests the use of fisheries management and conservation measures such as fish-aggregating devices, stocking of certified seed, and impact assessment of exotic species.

Phytoplankton, the primary producers in an aquatic ecosystem, also act as indicators of pollution by alterations in species composition and population structure. Study on plankton dynamics in relation to environment forms the base of any aquatic ecosystem management. So, a study on the variations in the plankton population influenced by abiotic factors was conducted in the Paleru Reservoir, India. A total of 48 plankton genera belonging to 9 classes were recorded. The Shannon-Wiener diversity index ranged from 1.098 to 2.615 with temporal variations. Plankton density showed significant (p ≤ 0.05) spatial variations with the highest density at the cage site irrespective of the season (4.126 × 105 ± 199 cells/litre, 2.814 × 105 ± 72.5 cells/litre and 3.197 × 105 ± 52.5 cells/litre during pre-monsoon, monsoon and post-monsoon, respectively). Seasonal analysis revealed significantly (p ≤ 0.05) high plankton density during pre-monsoon, followed by post-monsoon and monsoon respectively. The reservoir is moderately polluted as established from the diversity index and the Algal Genus Pollution Index except at the cage site where it receives a polluted status. The relationship of plankton distribution with the environment was established employing canonical correspondence analysis and correlation coefficient. Phosphate-P, nitrate-N, transparency, hardness, pH and dissolved oxygen are the major abiotic factors influencing the plankton distribution in Paleru. Even though Cyanophyceae dominated the plankton population, there was no plankton bloom-associated toxicity, indicating the health and dynamic nature of the reservoir. However, significantly high plankton density indicating a polluted status at the cage site reveals the influence of cage culture.

The pattern of a fish assemblage of a large reservoir, Stanley (also called as Mettur) in Peninsular India was studied to derive various management protocols, specifically fish enhancement. The investigation was carried out in the spatial and temporal scale of the reservoir during 2017–2019. A total of 52 species belonging to 35 genera were recorded indicating high species richness. Simpson (0.17), Shannon (0.17), dominance (0.104), and evenness (0.52) indices did not show significant differences among zones whereas there was a significant difference during different seasons. On a temporal scale, maximum species were recorded in monsoon (47) followed by post-monsoon (43) and pre-monsoon season (33). On a spatial scale, it represented that riverine (47) and transitional zone (37) showed more species richness compared to lacustrine zone (30). Based on the catch structure of this reservoir, it is evident that exotic fishes play a major role in the recent past. One species under critically endangered and endangered, three species under near threatened, and two under vulnerable species were observed in the catch during this study period. The trophic guild of fishes showed the dominancy of planktivores. Abiotic factors such as temperature, pH, and chlorophyll were found directly influencing the species abundance. The study suggested management measures, including observation of closed fishing season, protection of breeding grounds, use of fish aggregating devices, mesh size regulation, and fish seed stocking in the reservoir.

For natural ecosystems as well as human development, freshwater bodies like reservoirs are critically important. Krishnagiri reservoir, a moderately impacted tropical reservoir of India, is an important source of freshwater. However, eutrophication status due to anthropogenic activities is a major threat to this reservoir. This endeavour aimed to determine the spatio-temporal differences for selected (21) limnological parameters along with trophic status of Krishnagiri reservoir for its sustainable management. Samples (water and plankton) were collected from 11 sites covering entire reservoir during pre-monsoon, monsoon and post-monsoon season. Limnological parameters showed some spatio-temporal variations, the season has more impacts on water quality than sites as evidenced by cluster analysis. Principal component analysis distinguished the seasons based on major influencing water quality parameters. The reservoir trophic status fluctuated from eutrophic to hyper-eutrophic. Water quality index showed that the reservoir falls under unsuitable category. Additionally, cyanobacterial bloom formation was observed in all the seasons, with dominance of Microcystis sp. This investigation can be used as a baseline for studies pertaining to nutrient and sediment loading, and immediate action is required for employment of integrated management plan to restore this aquatic ecosystem. The study also recommends strategies for sustainable management of the aquatic bioresources.