Nutrient Retention by Fish in a Multispecies Recirculating Aquaculture Facility

R.C. Summerfelt, and C. R. Penne

Footnote
International Journal of Recirculating Aquaculture 8 (2007). All Rights Reserved
© Copyright 2006 by Virginia Tech and Virginia Sea Grant, Blacksburg, VA USA

ABSTRACT

Nutrient (N and P) content of the dry weight gain of fish relative to N and P content of the dry weight of feed was used to determine nutrient retention in a commercial recirculating aquaculture facility.  The culture system had five 39.2m3 dual-drain culture tanks, one tank each with largemouth bass (Micropterus salmoides), hybrid striped bass (aka sunshine bass, Morone chrysops  x Morone saxatilis ), and rainbow trout (Oncorhyncus mykiss), and two tanks with walleye (Sander vitreus).  On the first day, most rainbow trout (643 g) and walleye (497 g and 398 g) were market size whereas the largemouth bass (73 g) and hybrid striped bass (96 g) were fingerlings.  Measured for a 56-d interval, the range in nutrient retention was 12.0 to 44.1% for N 14.8 to 53.8% for P.  Market-size rainbow trout had the slowest growth and correspondingly low levels of nutrient retention; likewise, the larger walleye had nearly half the retention rates of the smaller walleye.  Highly significant (P ≤ 0.01) positive correlations occurred between retention of N and P, protein efficiency ratio, and net protein utilization, but inversely related to food conversion ratio.  Total ammonia nitrogen (g kg-1 feed fed) in the culture tank was inversely related to nitrogen retention.  Values for TAN production ranged from 2.9 to 6.9% of daily feeding rate, important information for sizing biofilter requirements.  This study demonstrated an interaction between fish age or size, growth rates, temperature, feeding rates, nutrient content, and protein retention.