Differences in Lateral Line Morphology between Hatchery- and Wild-Origin Steelhead

Abstract

Despite identification of multiple factors mediating salmon survival, significant disparities in survival-to-adulthood among hatchery- versus wild-origin juveniles persist. In the present report, we explore the hypothesis that hatchery-reared juveniles might exhibit morphological defects in vulnerable mechanosensory systems prior to release from the hatchery, potentiating reduced survival after release. Juvenile steelhead (Oncorhynchus mykiss) from two different hatcheries were compared to wild-origin juveniles on several morphological traits including lateral line structure, otolith composition (a proxy for auditory function), and brain weight. Wild juveniles were found to possess significantly more superficial lateral line neuromasts than hatchery-reared juveniles, although the number of hair cells within individual neuromasts was not significantly different across groups. Wild juveniles were also found to possess primarily normal, aragonite-containing otoliths, while hatchery-reared juveniles possessed a high proportion of crystallized (vaterite) otoliths. Finally, wild juveniles were found to have significantly larger brains than hatchery-reared juveniles. These differences together predict reduced sensitivity to biologically important hydrodynamic and acoustic signals from natural biotic (predator, prey, conspecific) and abiotic (turbulent flow, current) sources among hatchery-reared steelhead, in turn predicting reduced survival fitness after release. Physiological and behavioral studies are required to establish the functional significance of these morphological differences.

Are trunk lateral line anomalies and disoriented scale patterns in European seabass (Dicentrarchus labrax) influenced by genetics?

“…Their results highlight that: 1) the faster the developmental rate, the lower the number of lateral line scales in farmed fish; 2) an anomalous development of a chemosensory organ could be promoted by unsuitable rearing conditions. In farmed steelhead trout (Onchorhynchus mykiss), Brown et al (2013) found significantly fewer free neuromasts of the lateral line than in wild steelhead, suggestive of functional deficits in lateral line-mediated behaviors, and perhaps reflective of behavioral deficits that were reported previously. According to Carrillo et al (2001), the absence of some sectors of the lateral line increases the possibility of deficient sensory reception.…”

Effects of hydrokinetic turbine sound on the behavior of four species of fish within an experimental mesocosm

“…These results suggest that sound emanating from turbines might play a role in turbine avoidance, and raises the question of how cumulative sound from turbine arrays could influence migratory behavior. An important caveat when interpreting results from the rainbow trout utilized in the present study stems from observed abnormalities in the otolith structure and auditory brain response in hatchery-reared salmonids (Oxman et al, 2007;Chittenden et al, 2010;Brown et al, 2013, Wysocki et al, 2007. In addition to morphological differences, behavioral differences have also been observed between wild and hatchery salmonids (Chittenden et al, 2010) which suggests that inferences from experimental results with hatchery fish to wild stocks should be done with caution.…”

Sensory ecology of the fish lateral‐line system: Morphological and physiological adaptations for the perception of hydrodynamic stimuli

“…Intraspecific differences in lateral‐line morphology were found between wild‐caught and hatchery‐reared migratory O. mykiss juveniles. Wild animals had significantly more SNs than hatchery‐reared juveniles, although the number of hair cells within individual neuromasts was not significantly different between groups (Brown et al ., ). In addition, wild and hatchery‐raised migratory O. mykiss had different otolith composition and brain mass, which may have other behavioural consequences.…”

“…This supports the notion that different hydrodynamic conditions during development can result in differences in the anatomy of a sensory system. In the case of migratory O. mykiss , the reported differences predict a reduced sensitivity to biologically important biotic and abiotic hydrodynamic signals and consequently a reduced survival fitness after release (Brown et al ., ).…”

“…In farm-reared gilthead sea bream Sparus aurata (L. 1758) the lateral-line scales were missing while the underlying canal was still present, whereas in the somatic-scale deformity the lateral-line canal was missing but covered with normal somatic scales (Sfakianakis et al, 2013). Morphological abnormalities of these types are not necessarily a consequence of different hydrodynamic conditions experienced during rearing but could also be caused by the high density of animals in hatcheries, which results in more interactions with a concomitant higher rate of deformations and ablations (Brown et al, 2013).…”