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Context: There is a global problem with ongoing riverine infrastructure projects where, despite knowledge of potential environmental impacts, there is rapid development, often without appropriate environmental safeguards. This results in fragmentation of riverine fish communities, especially diadromous species. Understanding freshwater fish larval ecology is critical to provide insight into the likely impacts of these projects. Aims: To assess fish larval biodiversity on the basis of DNA barcoding, abundance and its distribution pattern in the Cibareno River. Methods: Fish larvae were collected at six locations in the Cibareno River. The larvae were identified by DNA barcoding. Key results: A notable disparity was seen in the distribution of larval abundance in different locations. The non-native species, Poecilia reticulata , was the most abundant larval species, with an intraspecific diversity of 0.003 (99.7% similarity). The upstream area exhibited a lower level of larval species diversity than did the downstream area. Conclusions: Genetic identification can reliably identify fish larvae and determine their spatial riverside distribution in the Cibareno River. The conservation of connectivity maintains fish community integrity and diversity between upstream and downstream locations in the weir building plan. Implications: This discovery emphasises the relevance of larval identification in fish biodiversity assessment and sustainable fisheries resource monitoring. This study investigated the identification and distribution of fish larvae in the Cibareno River, which is being modified by construction of a 3.25-m weir. Larval fish diversity is slightly lower in upstream reaches. Alien guppies were abundant. Genetic identification is essential for understanding the diverse species of fish larvae present. Implementing sustainable fisheries management practices requires this information. [ABSTRACT FROM AUTHOR]

The Cibareno River in Sukabumi, West Java, is the habitat of Tor tambra, one of Indonesia's most highly valuable native freshwater fish species. The native fish population in this river may be threatened by the planned weir construction. The study aims to examine the food and feeding habits of Tor tambra in the Cibareno River. This study was carried out for four months (May, June, July, and September 2022) at six locations in the Cibareno River. A total of 61 individuals of T. tambra displayed an isometric growth pattern with good condition factor. Aquatic insects were the primary food, with nematodes and phytoplankton acting as supplements. Plant seeds were often eaten as an extra source of food. These results were supported by fish morphometric data such as relative mouthwidth and relative gut length, which showed that they are omnivorous and tend to be carnivorous. In addition, the relative eye diameter of the fish indicates that Tor tambra is a diurnal forager. The findings suggest that both in-situ and ex-situ conservation methods are viable options for the preservation of Tor tambra in the Cibareno River.

A fishway is an engineered structure designed to help fish navigate past artificial barriers in rivers such as dams, weirs and regulators. An effective fishway design requires an understanding of fish biodiversity and migration requirements of the local community.To support the conceptual design of a fishway at Caringin Weir in the Cibareno River in Indonesia, we conducted a fish biodiversity assessment using experimental fishing and an eDNA metabarcoding survey.In early 2022, experimental fishing was conducted at six sampling sites upstream and downstream of the planned weir, and the sites were surveyed seven times during the wet and dry seasons. Environmental DNA sampling was conducted once during the wet season at each of the six sites.A total of 72 aquatic species were detected, comprising 40 fish species and seven crustacean species captured during experimental fishing and 36 fish species identified through eDNA metabarcoding. Twelve fish species (18.46%) were detected using both methods. The total number of all species caught and species richness in experimental fishing varied significantly between upstream and downstream areas (p < 0.05), but there were no significant differences between seasons (p > 0.05). There was also a significant difference in the species richness upstream and downstream using eDNA metabarcoding (p < 0.05). There were also numerous diadromous species, further highlighting the need for an effective fishway design to enable these species to complete their migrations.Based on the species present, migratory behaviour and economic importance, we prioritised six fish and crustacean species to be considered during fishway design: Anguilla marmorata, Tor tambra, Barbodes binotatus, Sicyopterus sp., Rhyacichthys aspro and Macrobrachium sp. [ABSTRACT FROM AUTHOR]