An Improved Photo-Electric Fish Egg Counter

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Abstract
We describe an improved design and operating procedure for a photo-electric fish egg counter. The design was simplified so that the apparatus can function as a flow-through system using tap water. The procedure for operating the counter was changed so that coincidence counting can be corrected for. Triplicate fecundity determinations, made gravimetrically for 10 randomly selected Pacific herring (Clupea harengus pallasi), were repeated using our method to compare the accuracy and precision of estimates made with both procedures. Mean fecundity estimates did not differ significantly between methods. The precision of estimates made using the counter was at least sixfold greater, and single determinations were accurate to within 5% of the true mean value with 95% probability. Our procedure is also less tedious and about 70% faster than the gravimetric method. The counter, unmodified, should be capable of counting eggs from 25 marine and 6 freshwater fish species. We believe that it can be easily adapted to count eggs that differ substantially in size from those of Pacific herring.

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