Effect of size grading on the growth performance of shortfin eel (Anguilla australis) during its yellow stage

Abstract

It is generally believed that size grading in a fish farm improves the total biomass output, because it will minimise the stress imposed by larger individuals over small individuals, resulting in higher feed intake and growth rate. The objective of this study was to evaluate the effect of size grading on individual growth performance of yellow New Zealand shortfin eel (Anguilla australis). A 109 day trial was conducted in a recirculation aquaculture system (RAS) with 103 eels of similar initial weight (101 ± 12 g). All eels were individually marked by PIT (passive integrated transponder) tags. On day 42, eels were graded to establish the following groups: only small eels (S-graded ≤ 135 g), only large eels (L-graded > 135 g), and small and large eels together (S-ungraded and L-ungraded). The large eels showed better specific growth rate (SGR), feed intake (FI) and feed conversion ratio (FCR) than the small eels. Nevertheless, no significant differences were found either between L-graded and L-ungraded or between S-graded and S-ungraded. The age of eels was not significantly different between groups. These findings suggest that the individual growth rate performance of the eels is not primarily a consequence of social interaction among tank-mates.

Effect of size grading on growth of yellow Pacific shortfin eel (Anguilla bicolor pacifica)

“…In addition, large‐graded eels grew bigger than small‐graded eels even when reared in separate tanks. Results suggest no social hierarchy effects on growth depensation as reported in the present and earlier studies on eels (García‐Gallego & Akharbach, 1998; Hirt‐Chabbert et al ., 2014) and other species such as Atlantic cod Gadus morha L. (Lambert & Dutil, 2001), yellow perch Perca flavescens (Wallat et al ., 2005), Nile tilapia Oreochromis niloticus (Saoud et al ., 2005), African catfish C. gariepinus (Martins et al ., 2005, 2006) and spinefoot rabbitfish S. rivulatus (Ghanawi et al ., 2010). Factors such as the size of the rearing tank, individual population density, frequency and amount of food and the presence or absence of physical structure in the tank may be responsible for the absence of social hierarchy effects.…”

Cage culture of tropical eels, Anguilla bicolor pacifica and A. marmorata juveniles: Comparison of growth, feed utilization, biochemical composition and blood chemistry

“…The experimental trial was conducted in three outdoor concrete tanks each measuring 2 × 2 × 1.5 m. Each tank was supplied with deep well water at a flow rate of 200 mL per minute and covered with a double black net to reduce the light intensity (Hirt‐Chabbert et al, 2014). Eel juveniles (initial weight (mean ± standard deviation [SD]): 1.73 ± 0.14 g; total length (TL; mean ± SD): 127.88 ± 16.56 mm) of both A. bicolor pacifica and A. marmorata were each randomly stocked at 30 eels per cage in triplicate 1 × 1 × 1.5 m hapa net cages (1 mm mesh size) suspended in outdoor concrete tanks in a complete randomized design.…”

Enabling and driving aquaculture growth in New Zealand through innovation

“…Two finfish species of high value, yellowtail kingfish (Seriola lalandi) and hāpuku (groper, Polyprion oxygeneios), have been identified in a review by Symonds et al (2014) as being biologically, technically and economically viable for farming in New Zealand. Size-grading effects were examined for New Zealand shortfin eels (Anguilla australis) with consequences for improved farming in tank operations (Hirt-Chabbert et al 2014). Zamora et al (2014) investigated an innovative approach of co-culturing sea cucumbers (Australostichopus mollis) under Pacific oyster (Crassostrea gigas) farms, and their findings show good synergy and high feasibility for co-culturing these species.…”