We describe an artificial propagation procedure and simple ploidy discrimination techniques using erythrocyte major axis length for largemouth bass Micropterus salmoides. Hormonal treatments of 5 mg/kg of carp pituitary and 50 μg/kg of leutinizing hormone‐releasing hormone (LHRH) produced viable gametes in 21‐24 h, and triploidy was induced using a pressure treatment of 563 kg/cm2 on embryos for a 1‐min duration exactly 5 min following fertilization. We produced about 500 fingerling triploids and about 500 diploid controls, and verified genetic status of a subset of each group using flow cytometry. Erythrocyte length was measured for 10 known diploid and 10 known triploid individuals. Remaining fish were internally microtagged with group‐specific tags and mixed to test the model. We developed ploidy discrimination intervals based on the 99% confidence limits of mean erythrocyte length (MEL, N= 25 erythrocytes) for individual fish, which were 14.43‐16.66 μ.m for triploids, and 10.23‐13.62 μm for diploids. Logistic regression provided the discrimination model: Ploidy status (±) = ‐196.16 + 13.97 x MEL, with positive (+) outcomes considered triploid. Both discrimination techniques were 100% effective at differentiating ploidy of the 22 microtagged largemouth bass recollected from the mixed population. We did not observe a significant change in erythrocyte length as fish size increased, indicating that erythrocyte length is an accurate predictor of ploidy for all sizes of largemouth bass.

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Dissolved oxygen and un-ionized ammonia concentrations were monitored in 12 0.04 ha earthen ponds stocked with 10 000 channel catfish, Ictalurus punctatus,/ha. Gill, liver and trunk kidney tissue samples were removed periodically for histological examination. Total ammonia and dissolved oxygen levels were in the ranges reported for catfish culture at this level of intensity. Average un-ionized ammonia nitrogen concentrations ranged from 20 to 67 pg I-' and average daily maxima ranged from 63 to 183 pg1-I. Gill lesions characteristic of un-ionized ammonia exposure were common in fish from all ponds.

Cold stress was identified as an important factor influencing both reservoir-wide mortality and impingement of threadfin shad, Dorosorna perenense, during the period October 1976 to April 1977 in Watts Bar Reservoir, Tennessee. Relative numbers and size frequency of impinged threadfin shad were similar to the relative numbers and size frequency of shad preyed upon by sauger, Sfizosredion canadense, and skipjack herring, AIosa chrysochloris. This relationship implies that the factor mainly responsible for impingement, low temperature, also influences prey vulnerability. Threadfin shad made up 99% of the combined diet of sauger and skipjack herring from November until the threadfin shad disappeared in January. These predators did not readily switch to alternative prey in the short term, but by the next autumn 25-100% of the diet was alternative prey. Reappearance of threadfin shad the year following mass mortality and ability of the predators to vary their diet emphasize the resilient nature of some predator-prey systems.