The ecology of larval and juvenile fishes in lowland rivers, with particular emphasis on foraging

Tewson, Lauren Haley

Abstract

FEEDING ECOLOGY OF 0+ FISHES
There are numerous biotic and abiotic factors that affect the abundance of cyprinid fish stocks in rivers, many of which are poorly understood. The role of food availability during critical life stages is one of these factors that may determine the growth and survival of 0+ fishes, and ultimately their recruitment to adulthood. Until the main factors affecting recruitment of cyprinid fishes are better understood, informed/appropriate management actions cannot be undertaken. For this reason temporal, spatial and inter-specific influences affecting the prey availability, feeding ecology and condition of 0+ fishes were studied in experimental and wild conditions to improve the understanding of feeding ecology for 0+ fishes in rivers and the effect this has on the health of the individual fish.

This study revealed diel variation in fish species composition, prey availability, diet composition, feeding activity and prey selection of larval and 0+ juvenile fishes. Five surveys were carried out in total, until the fishes reached juvenile stage, in the River Trent. There was circumstantial evidence of zooplankton migration in some species, for example, densities of Rotifera in the margins declined at night, suggesting migration into open waters. Densities of 0+ fishes were generally higher at night in three surveys, but higher in daylight in two surveys. This may have been a result of predator avoidance as more >0+ pike and perch were found in the margins at night. There was also a significant increase in spined loach and bullhead at night compared to daylight. Gut fullness of 0+ juvenile roach and perch increased at night, but there was a reduction in gut fullness at night for larval roach and perch, suggesting a switch in feeding behaviour during ontogeny that was also evident in electivity indices and prey availability. Seasonal variations in prey availability and feeding ecology of 0+ roach and bream were studied on the River Trent, which revealed a significant reduction in feeding activity of both species from summer to winter, but this did not affect the condition of the fishes, which remained constant across all seasons. Significant seasonal differences in the diet composition were found in 0+ bream, but not 0+ roach.

Spatial variations in prey availability (composition, density and diversity), feeding ecology (diet composition, feeding activity and prey selection) and condition of 0+ fishes were studied using point abundance sampling on a mesohabitat scale in the River Ancholme to investigate the influence of habitat type (floating-leaved, emergent or submerged vegetation). The highest densities of most zooplankton taxa were found in emergent and floating-leaved vegetation (the least complex habitats) compared with submerged vegetation (the most complex). Feeding activity was higher for larval and 0+ juvenile roach than bream in all vegetation categories. Gut fullness of larval roach was highest in submerged vegetation, suggesting that the complex structure did not affect the feeding activity of 0+ roach. In general, selection was higher in simple vegetation categories than complex vegetation categories, even though the same prey was available in most habitats, indicating that prey availability was not the only factor influencing feeding ecology of 0+ roach and bream and that habitat complexity influences prey choice. Nonetheless, this did not influence the condition of roach and bream between the different vegetation categories, which remained constant.

The effects of interspecific interactions on the diet composition, prey selection, growth and condition of 0+ roach and bream were studied in allopatric (single-species) and sympatric (mixed-species) fish populations established in enclosures at Calverton Fish Farm, Nottinghamshire. This study found a significant influence of interspecific interactions on the diet composition and prey selection of 0+ fishes. There was evidence of resource partitioning when roach and bream larvae were in sympatry, which suggested that feeding behaviour of both species was negatively affected by interspecific interactions. By comparison, interspecific interactions had no significant influence on the length, weight or weight-length relationships of 0+ roach and bream. In addition, the condition of roach was not affected by the presence of bream, but there was a small but significant deterioration in the condition of bream in the presence of roach. These results were compared to wild conditions in the River Trent, which generally supported the findings at Calverton even though the densities at Calverton were higher. This information will improve understanding of the feeding ecology of 0+ fishes during early development, which can be used in the management and rehabilitation of fish populations and fluvial habitats, as well as improving growth and survival in aquaculture facilities, and inform research sampling strategies when studying juvenile fish populations.

Citation

Tewson, L. H. (2012). The ecology of larval and juvenile fishes in lowland rivers, with particular emphasis on foraging. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4214479

• Thesis Type: Thesis
• Deposit Date: Sep 9, 2013
• Publicly Available Date: Feb 23, 2023
• Keywords: Biological sciences
• Public URL: https://hull-repository.worktribe.com/output/4214479
• Additional Information: Department of Biological Sciences, The University of Hull
• Award Date: Aug 1, 2012