SUMMARY. In this highly productive chalk stream the stone loach, sampled by electrofishing over a 30 month period, had a high growth rate reaching a mean length of 65 mm in 1 year and 93 mm in 2 years. The fish were short‐lived in contrast to most slow‐growing populations in the U.K. and Finland with 11 group fish comprising 8.8% and III group fish only 1.1% of the total number. The loach were fractional spawners: a 75 mm female produced an estimated 10,620 eggs between late April and early August totalling 46% of the loach's initial weight. In March and April some small 0 group females contained only poorly developed eggs and up to 10% of 0 group fish may have failed to spawn. Amongst loach >52 mm in length in March and April there was an exponential relationship between absolute fecundity and fish length but no relationship between relative fecundity and length. There was. however, a relationship between fish length and both gonadosomatic index and maximum egg size, which may indicate that large fish began to spawn first.
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Mills et al. (1983) studied this question.