Nests of oyster toadfish Opsanus tau with guardian males were transported from Waquoit Bay, Massachusetts, to the Marine Biological Laboratory in Woods Hole, Massachusetts. Following larval detachment from the nest, the offspring were separated from the males and placed into culture tanks with flow-through seawater. The juveniles were initially fed adult brine shrimp Artemia spp. supplemented with small pieces of frozen squid Loligo spp. During the second year of the study, the majority of the diet was squid supplemented with locally available food. Fish were maintained at different temperatures (approximately 15°C, 20°C, and ambient) and densities (2-90 fish/m2). Although the culture density did not have an appreciable effect on growth, fish maintained in warmer water grew significantly faster than fish kept at cooler temperatures. After 2 years, the fish reared in warm water averaged 10.0 cm and 40.5 g, while those reared in cold water averaged 6.5 cm and 11.0 g. Growth in weight was shown to be exponential from day 76 to day 200, with rates of 1.4% and 0.38% body weight per day at 20°C and 15°C, respectively, an almost fourfold difference. Beyond day 200, growth in weight at both temperatures was best fitted by a power function; however, there was no significant difference in the slope of the growth curve between the two temperature groups. Thus, temperature did not accelerate growth rates from day 225 onward. Survival rates were greater than 68% in four of the five treatment groups. Despite constant high temperatures and food availability throughout the winter months, oyster toadfish underwent a quiescent period during the second year of life and exhibited minimal growth during this time, indicating that shortened day length may affect growth rates.
Bibliographical noteFunding Information:
Thanks to Ed Enos for providing data on the history of oyster toadfish collections at the MBL. Heather Wesp, Maureen O’Neill, and Kathleen Tang provided expert animal care. Bill Mebane provided invaluable help in establishing and maintaining the aquaria. Chris Weidman and Kelly Chapman from the Waquoit Bay Natural Estuarine Research Reserve provided logistics and support for our field collecting sites. Support was provided by the Marine Models in Biological Research Program, University of Minnesota Grant in Aid, Na- tional Aeronautics and Space Administration Life Science Fellowship, MBL Associates Fellowship, and National Institutes of Health grant DC01837.