No abstract

Grass Carp Ctenopharyngodon idella, a nonnative species to North America, are known to cause negative impacts to aquatic habitats and aquatic communities. Numerous fisheries techniques have been used in an attempt to control or eradicate Grass Carp, including electrofishing. However, electrofishing efficiency for Grass Carp has been variable, and optimum electrofishing waveforms and parameters for inducing a capture-prone response have not been determined. The objective of this study was to determine the optimum electrofishing waveforms and parameters to induce a capture-prone response at various water temperatures and conductivities in juvenile Grass Carp in a controlled, laboratory setting. Results indicated that rectangular pulse waveforms with 60-100 Hz frequencies were most effective for immobilization of juvenile Grass Carp. While all duty cycles tested (20-48%) at these frequencies were effective we found that at 60 Hz and 80 Hz frequencies, 24% and 30% duty cycles, respectively, may be more effective. Water temperature was positively related to voltage gradient immobilization thresholds whereas ambient water conductivity and fish size were inversely related to voltage gradient immobilization thresholds. This study provides important information to those seeking to control, eradicate, or detect Grass Carp using electrofishing and provides a framework for future studies focusing on adult Grass Carp.

Eggs of silver carp Hypophthalmichthys molitrix absorb water after release from the female, causing them to become turgid and to increase substantially in size. The volume of water that diffuses within an egg is most likely determined by (1) the difference in ionic concentration between the egg and the water that surrounds it and (2) the elasticity of the egg membrane. Prior observations suggest that silver carp eggs may swell and burst in soft waters. If water hardness affects silver carp reproductive success in nonnative ecosystems, this abiotic factor could limit silver carp distribution or abundance. In this study, we tested the effect of water hardness on silver carp egg enlargement and hatching success. Groups of newly fertilized silver carp eggs were placed in water at one of five nominal water hardness levels (50, 100, 150, 200, or 250 mg/L as CaCO3) for 1 h to harden (absorb water after fertilization). Egg groups were then placed in separate incubation vessels housed in two recirculation systems that were supplied with either soft (50 mg/L as CaCO3) or hard (250 mg/L as CaCO3) water to evaluate hatching success. Tests were terminated within 24 h after viable eggs had hatched. Eggs that were initially placed in 50‐mg/L water to harden were larger (i.e., swelled more) and had a greater probability of hatch than eggs hardened in other water hardness levels. Unlike the effect of water hardness during egg hardening, the water hardness during incubation appeared to have no effect on egg hatching success. Our research suggests that water hardness may not be a limiting factor in the reproduction, recruitment, and range expansion of silver carp in North America.

Low recovery o f transplanted mussels often prevents accurate estimates o f survival. W e developed a method t h a t provided a high recovery o f transplanted mussel s and a1 1 owed f o r a re1 i abl e assessment o f mortal i t y .A 3 x 3 m polyvinyl chloride (PVC) pipe g r i d was secured t o the sediment w i t h i r o n r e i n f o r c i n g bars. The g r i d was divided i n t o nine 1-mZ segments and each treatment segment, was stocked w i t h 100 marked mussels.The recovery o f mussels a f t e r s i x months exceeded 80% i n a l l but one treatment group. INTRODUCTIONFreshwater mussels are relocated as a p a r t o f state and federal conservation and management programs. Frequent1 y, mussel s are moved from construction o r dredging zones t o unaffected s i t e s upstream (Oblad 1980, Harris 1984, 1986, Harris e t al. 1992, Jenkinson 1989). E f f o r t s have also been made t o reestablish mussels i n restored streams (Ahlstedt 1979, Sheehan e t a1 1989, Hubbs e t a1 1991). Recently, threatened mussel species were relocated t o protect them from the exotic zebra mussel

The common carp Cyprinus carpio is a major problem for fisheries and wildlife managers because its feeding behavior causes degradation of valuable fish and waterfowl habitat. This study was designed to evaluate the effectiveness of an antimycin‐impregnated bait for control of common carp. The toxic bait contained fish meal, a binder, antimycin, and water. The ingredients were mixed together and made into pellets. This bait was force‐fed to common carp or administered in a pond environment, where fish voluntarily fed on the bait. The lowest lethal dose in the force‐feeding study was 0.346 mg antimycin/kg of fish and doses that exceeded 0.811 mg antimycin/kg were toxic to all fish. On three occasions, adult common carp held in 0.004‐ha concrete ponds were offered 10 g of toxic bait containing 5.0, 7.5, and 10 mg antimycin/g of bait and the mean mortalities 96 h later were 21, 35, and 51%, respectively. Three tests were conducted in 0.04‐ha earthen ponds each containing 100 adult common carp; these fish were offered 50 g of the toxic bait that contained 10 mg antimycin/g, and the mean mortalities (96 h) were 19, 32, and 74%. Toxic baits should be used in conjunction with other management techniques, and only when common carp are congregated and actively feeding, and when few nontarget bottom‐feeding species are present.