Fecundity and spawning in a deep-water cirromorph octopus

Reproductive characteristics of cirromorph octopuses, assigned to the speci es Opisthoteuthis grimaldii, were sampled as a commercial fishing by-catch on the Hebrides Slope, west of Scotland. A total of 254 specimens (99 femal e, 155 males), retrieved from bottom trawls fished at 750 to 1500 m depth, were examined. A maximum of 2097 eggs was counted in a single female ovary (mean female body weight 1242.8 g), most of them <1 mm in length. At egg le ngths over 1 mm, diminishing numbers of eggs were present in I mm size cate gories up to a maximum of approximate to 10 mm. At body sizes >500 g (wet w t), arid in every female >750 g (max. female weight recorded in the sample was 2959 g), a succession of unattached eggs was present in the proximal ov iduct and a single, unattached mature egg occupied the tip of the distal ov iduct. These females were assumed to be in spawning condition and the chara cteristics of egg distribution in the reproductive tract to be consistent w ith sequential release of individual eggs and continuous spawning throughou t the growth period and lifespan of the mature octopus. In pre-spawning fem ales there was a positive relationship between estimated egg numbers and ma ximum egg size. After the onset of spawning there was no significant furthe r increase in estimated potential fecundity over the body-size range 500 to 3000 g. Follicular sheaths remaining in the ovary after release of eggs in to the proximal oviduct were counted and used to estimate the total number of eggs released up to the time of capture. Follicular sheaths first appear ed at 500 to 650 g body weight and increased steeply in number to >1000 in females >1500 g. Two individuals were found with ovarian follicular sheaths but with no terminal egg in the distal oviduct; these were assumed to have released their egg just before capture. Summation of the number of follicu lar sheaths counted plus the number of eggs estimated as remaining attached in the ovisac, provided a revised estimate of total potential fecundity an d raised the estimate for any individual to a maximum of 3202 eggs (mean = 1396 eggs).