Studies of appetite variation in juvenile Atlantic cod (Gadus morhua L.) using demand feeding systems

Ablitt, Helen (2009) Studies of appetite variation in juvenile Atlantic cod (Gadus morhua L.) using demand feeding systems. PhD thesis, University of Glasgow.

Abstract

This thesis covers two studies based on the feeding of juvenile Atlantic cod (Gadus morhua). The first study was carried out using an AQl interactive feedback feeding system and investigated their feeding patterns, both seasonal (chapter 2) and daily (chapter 3). The second study involved designing an on-demand feeding system for juvenile cod, then examining the process of the fish learning to use the feeder, focusing on the roles of individual fish. The first trial was carried out in two sections, the first from March until August 2004 and the second form November 2004 until February 2005. Five 124 litre tanks were stocked with cod of 5 grams. The tanks were equipped with an AQl feeding system with infra red sensors at the outlet of each tank. The system added test feeds every 30 minutes and the feed input each minute was recorded to an attached computer. The sensors were affected by suspended solids in the water, causing false readings of waste pellets, causing under feeding. The data set was therefore cleaned up by removing affected days. Chapter 2 focuses on the seasonal changes in feed consumption of the cod. The mean daily feed input (as a percentage of bodyweight per day, BWD) varied between 0 and 10%, with the mean being around 5%. The feed input (%BWD dropped to its lowest levels around early summer, the opposite result to that expected. The effects of temperature and photoperiod on feed input were also opposite to the expected outcome, when the day length was longer, and when the temperature was high, the feed intake dropped. There was a significant pattern of autocorrelation in feed input, leading to the conclusion that juvenile cod appetite is affected by a medium term internal rhythm. Chapter 3 focuses on the daily feeding patterns of the juvenile cod. The main pattern found during the first part of the trial was a significant dawn peak when up to 40% of the days feed was consumed. The remaining part of the day was spent browsing. In the second part of the trial, there were a lot less definite patterns; there was a trend towards browsing over a full 24 hour day with heavier feeding nocturnally and short phases of crepuscular feeding, again with continuous light browsing at other times. The reasons for the differences in feeding pattern are discussed and the peak feeding hour and percentage nocturnal consumption are investigated. Chapter 4 concentrates on the process of juvenile cod learning to use a demand feeder. Every group of fish learnt to use the demand feeder, though only one fish from each group was responsible for activating the trigger. That fish was also found to be the boldest when tested in a novel object test and its growth was significantly higher than the other fish in the group, it was named the trigger fish. Another group emerged at the other end of the scale; they did not interact with the sensor at all, nor approached the novel object. They were significantly smaller than all the other individuals and gained the least weight, in some cases, the fish lost weight.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Felicity Huntingford
• Keywords: Aquatic sciences, Animal sciences
• Date of Award: 2009
• Depositing User: Enlighten Team
• Unique ID: glathesis:2009-74027
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 23 Sep 2019 15:33
• Last Modified: 23 Sep 2019 15:33
• URI: https://theses.gla.ac.uk/id/eprint/74027