Experimental investigation of the effects of temperature and feeding regime on scale growth in Atlantic salmon Salmo salar post‐smolts

Abstract

Salmo salar post‐smolts were reared in seawater under controlled laboratory conditions for 12 weeks. The fish were exposed to three constant temperature treatments (15, 10.5 and 6°C) and four feeding treatments (constant feeding, food withheld for 7 days, food withheld for 14 days and food withheld intermittently for four periods of 7 days). Scale growth was proportional to fish growth across all treatments, justifying the use of scale measurements as a proxy for growth during the early marine phase. The rate of circuli deposition was dependant on temperature and feeding regime and was generally proportional to fish growth but with some decoupling of the relationship at 15°C. Deposition rates varied from 4.8 days per circulus at 15°C (constant feeding) to 15.1 days per circulus at 6°C (interrupted feeding). Cumulative degree day (°D) was a better predictor of circuli number than age, although the rate of circuli deposition °D−1 was significantly lower at 6°C compared with 15 and 10.5°C. Inter‐circuli distances were highly variable and did not reflect growth rate; tightly packed circuli occurred during periods without food when growth was depressed, but also during periods of rapid growth at 15°C. The results further current understanding of scale growth properties and can inform investigations of declining marine growth in S. salar based on interpretations of scale growth patterns.

Variation in the post‐smolt growth pattern of wild one sea‐winter salmon (Salmo salar L.), and its linkage to surface warming in the eastern North Atlantic Ocean

“…Thus, for example, from scale circulus measurements for Atlantic salmon smolts reared experimentally for 12 weeks, and at a range of temperatures and dietary regimes, Thomas et al . (2019) noted the rate of circulus deposition to increase with temperature. Circulus spacings did, however, show a complex interaction both with diet and temperature, and were widest at 10.5°C, narrower at 15°C and intermediate at 6°C.…”

Date of marine annulus formation in Atlantic salmon (Salmo salar) and implications for retrospective growth analyses using scales

“…These rates were selected based on assumptions provided by Friedland and Reddin (2000) which asserted that circuli are deposited at a rate of 14 days per circulus in winter and 7 days per circulus in spring and summer. These and similar circulus deposition rates have been standard in Atlantic salmon growth studies (Friedland et al ., 2005; Hubley et al ., 2008; Thomas et al ., 2019; Todd et al ., 2014).…”

“…For fish with leptoid scales, such as Atlantic salmon ( Salmo salar ), the scale radius increases approximately linearly as the fish grows in length (Fisher & Pearcy, 1990; Fukuwaka & Kaeriyama, 1997; Panfili et al ., 2002). As the radius increases, circuli (mineralized ridges that appear as concentric rings) are deposited, and the interaction between the scale's growth rate and circulus deposition rate determines the spacing between circuli (Thomas et al ., 2019). Bands of widely spaced circuli are considered to indicate periods of fast somatic growth when circulus deposition is relatively slow compared to scale radius growth (Fisher & Pearcy, 1990; Friedland et al ., 2000).…”

The sustainable use and exploitation of fishes

“…Some recreational fisheries are strongly affected by wider climatic and ecological factors; this includes those focussed on diadromous species such as salmon. Thomas et al (2019) present work based on scale measurements that furthers our understanding of Atlantic salmon Salmo salar growth in relation to temperature and feeding conditions.…”

“…Thomas et al . () present work based on scale measurements that furthers our understanding of Atlantic salmon Salmo salar growth in relation to temperature and feeding conditions.…”