An ecological approach to feed management in fish rearing ponds.

摘要

Channel catfish (Ictalurus punctatus) has been the most important cultured fish in the United States by yield and commercial value for the past 60 years, and at least 31 states stock this species into lakes and reservoirs as a sportfish. Catfish culturists have historically used a "black box" approach to feed management by only quantifying the effects of varied manufactured feed subsidies on mean fish size and yield at harvest. Alternatively, I sought to improve fish production efficiency and reliability by quantifying the complex effects of feed subsidies on fish diets, growth, and survival; the lower food web; and habitat quality in hatchery ponds.;To test the effects of feed subsidies on ecosystem dynamics, I conducted an experiment in age-0 catfish rearing ponds using three different rates of feed addition (no feeding, 1%, or 3% body-weight/day, BW/d). Ponds in the 3% BW/d treatment had low dissolved oxygen (DO) concentrations and their surface became covered by filamentous green algae. Further, the feed did not enhance or support production of live prey for fish (Chapter 1). By examining the fish gut contents, I found that adding feed to ponds did not alter the types or amounts of live prey items eaten through time (Chapter 2). Stable carbon and nitrogen isotopes further revealed that live prey entirely supported fish growth in all feeding treatments during weeks 1--3, and then live prey and the dry feed equally supported further fish growth in the fed ponds (Chapter 3). Although adding feed to ponds enhanced fish growth after week 3, fish survival did not differ among feeding treatments. To improve age-0 catfish production efficiency, I recommend managers next test a delayed first-feeding regimen against continuous and no-feeding treatments.;To test whether reduced feed provision could improve age-1 catfish production, I performed a separate pond experiment using 3% BW/d (historical) and 1% BW/d (reduced) feeding rates. Reducing the feeding rate from 3% to 1% BW/d increased the fraction of fish growth supported by live prey, but also slowed fish growth and produced smaller fish at harvest. However, because the 1% BW/d treatment ponds had similar fish survival and feed conversion ratios, produced fish with mean sizes at TL > 200 mm, and had higher DO concentrations, this reduced feeding rate warrants consideration for age-1 catfish production in sportfish hatcheries (Chapter 4).;Grand Lake St. Marys, the source water for the St. Marys hatchery, has been plagued by toxic cyanobacterial blooms in recent summers. To help the St. Marys hatchery staff identify the best times to fill and flush their catfish ponds with Grand Lake water, I quantified the seasonal phosphorus (P) dynamics in the reservoir. Phosphate-P concentrations in Grand Lake were > 300 mug P/L during the summers of 2009--2011, and were apparently driven by internal loading from sediments after establishment of cyanobacterial blooms during late spring. Because flushing ponds failed to improve water quality, St. Marys hatchery managers no longer use this production strategy during summer months (Chapter 5).