Can we teach a fish how to eat? The impact of bottom and surface feeding on survival and growth of hatchery-reared sea trout parr (Salmo trutta trutta L.) in the wild.

Tomasz Krepski,Robert Czerniawski,Fraser Andrew Januchowski-Hartley

doi:10.1371/journal.pone.0222182

Abstract

In this study we attempted to determine the effect of various feeding methods (bottom and surface feeding) used in the hatchery, on the survival and growth rates of hatchery-reared sea trout (Salmo trutta trutta L.) in the wild. Rearing was performed in two variants: a bottom-fed group (BFG) and a surface-fed group (SFG). At the end of the rearing time, we observed that BFG fish gathered at the bottom of tank, as opposed to SFG fish, which swam in the whole water column. After 4 weeks of rearing, the fish were released into two similar streams. After about 2 months the fish were captured and the foodbase of the streams were examined. 30 fish from each group have been randomly selected for stomach contents analysis. In the shallow stream the growth rates were better for the BFG fish than the SFG and also a significantly higher number of typical benthic taxa was found in stomachs of the BFG fish than the SFG fish. In the deeper stream more food was found in the stomachs of the SFG fish than in the BFG fish. The analyzed results showed that factors such as stream depth, current velocity, and turbulence can also affect the rearing success of juvenile salmonids in hatchery streams. Bottom feeding fish during rearing has a positive impact only on the fish in shallow watercourses, where there is no turbulence, and the food is not carried by the current drift or washed out from the bottom into the drift.

Highlights

Anadromous salmonids are one of the most endangered fish in the Baltic catchment area [1, 2, 3]
At the end of the rearing time, we observed that the bottom-fed group (BFG) fish gathered at the bottom of tank unlike the surface-fed group (SFG) fish, which swam in the whole water column
The SFG achieved significantly higher values of fork length and mass than the BFG (Mann–Whitney U test for fork length: df = 1, P < 0.0016; and Mann–Whitney U test for mass: df = 1, P < 0.0018) (Table 1)

Summary

Introduction

Anadromous salmonids are one of the most endangered fish in the Baltic catchment area [1, 2, 3]. The main reasons are difficulty in migrating to spawning sites, the harvesting of migrated adult fish, pollution, and the increase in nutrient content in streams, which contributes to the disappearance of spawning places [2, 4]; juvenile anadromous salmonids are absent in upper parts of streams. Common way of improving the population is to stock streams with hatchery-reared parr or smolt stages of the salmonids [5, 6]; this method is far from perfect because of the high mortality rate of hatchery-reared fry in the wild. Researchers are looking for methods that allow fish reared in artificial hatchery conditions to develop foraging skills, which improves their survivability once they are released into streams [11, 12]

Methods

Discussion

Conclusion