Would the presence of a larger fish, suppress aggression in smaller conspecifics?

“Whilst it was thought that the presence of a larger fish would suppress aggression in smaller conspecifics this did not occur. In fact aggression was significantly (P =0.036) higher when large trout were present during the first 4 weeks. No significant differences were found between other welfare indicators, self-feeder utilization or production parameters.”

From this interesting article below.

Aquaculture Research
Volume 43, Number 11 (October 2012)
	Can the presence of a large conspecific improve the production and welfare of groups of smaller self-feeder competent rainbow trout?
	Authors:	Matthew J. Flood, Chris Noble, Rem Kagaya, Mitsuo Tabata
	Author Affiliations:	no affiliations available
	Source:	Aquaculture Research, Volume 43, Number 11 (October 2012)
	Page Numbers:	1620 – 1627
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: unknown Location: Publisher’s Site Authentication: EBSCOhost EJS
	Abstract:	This study examined the production and welfare effects of including a large self-feeder competent rainbow trout, Oncorhynchus mykiss(Walbaum) (~665 g) in groups of smaller self-feeder competent conspecifics (~234 g). Costs and benefits were examined for both welfare (aggression, fin damage, condition and mortality) and production (self-feeder utilization and growth). The 8-week experiment used six groups of small trout; three treatment groups containing a large trout and three control groups. After 4 weeks the large fish were removed from treatment groups and added to control groups, thus reversing the treatments. Whilst it was thought that the presence of a larger fish would suppress aggression in smaller conspecifics this did not occur. In fact aggression was significantly (P =0.036) higher when large trout were present during the first 4 weeks. No significant differences were found between other welfare indicators, self-feeder utilization or production parameters. From a production and welfare perspective these results suggest that with the exception of initially increasing aggression larger fish do not represent a significant benefit or risk to smaller conspecifics being cultured in self-feeder equipped tanks, when all fish are self-feeder competent.
	Citation:	Matthew J. Flood, Chris Noble, Rem Kagaya, Mitsuo Tabata . Can the presence of a large conspecific improve the production and welfare of groups of smaller self-feeder competent rainbow trout?. Aquaculture Research, Volume 43, Number 11 (October 2012), pp. 1620-1627, <http://ejournals.ebsco.com/direct.asp?ArticleID=4EF1BFEAD3C61114F025&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4EF1BFEAD3C61114F025

 
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