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1. Freshwater ecosystems worldwide are experiencing native fish losses with severe threats to the conservation of freshwater biodiversity and ecosystem functioning, and the debate on whether the cause is biotic or abiotic disturbance is still open. 2. Temporal variation in fish assemblages was analysed over an 18 year period in 14 waterways of the lowland backwaters of the PoRiver in north-eastern Italy, which are important feeding, spawning and nursery sites for native fish. 3. In 1991, 14 native and eight exotic species were collected. In less than 20 years 10 native species underwent local extinction, three of which – Rutilus pigus, Rutilus aula, and Chondrostoma soetta – were endemic to the Padano-Veneto District in northern Italy. 4. Ordination of the data (MDS, CLUSTER, ANOSIM, SIMPER) showed a clear temporal gradient in fish community structure. After the establishment of the exotic predator Silurus glanis, some native species significantly declined in abundance and biomass (i.e. Alburnus arborella and Scardinius erythrophthalmus) or disappeared (i.e. Rutilus aula and Tinca tinca). Moreover, exotic species Cyprinus carpio, Ameiurus melas, and Carassius auratus from previous introductions, underwent significant changes in their abundance and biomass. No correlation was found between fish community structure and water quality parameters (BIOENV). 5. The success of exotic species, particularly S. glanis which thrived in this degraded habitat, seems to have led to the decline of native fish fauna in the canals of the lower portion of the Po River basin. Conservation strategies focusing on the containment of exotic species and habitat restoration are recommended

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Bivalves aquaculture is already considered a very sustainable for of food production and might become an essential pillar on which to develop future global food security. However, with the increase in production, a correspondingly great amount of waste will be produced all around the earth, principally in the form of shells, which can represent up to 90% of the fresh mollusk weight. Nowadays, shell waste has no notable use and is commonly regarded as waste, often dumped in landfill, or thrown back into the sea, causing a significant level of environmental concern, and resulting in a loss of natural and valuable resources. Bivalve shells are mainly formed by CaCO3, giving them the potential to become a promising secondary raw material for several applications, from a circular economy perspective. This paper aims to review the scientific literature of the last twenty years and the principal recent trends in shell waste reuse, describing applications that are already in place on a large scale in agriculture and livestock, soils, water and wastewater remediation, biodiesel production and biofilters, as well as niche applications that now simply have the potential to be scaled up.

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