Estimation of Male Reproductive Success of Marine Fishes

Abstract

The subject of reproductive potential of fish populations is dominated by studies on the female gender. Studies on male reproduction are relatively few, but have increased in number during the previous decade. The objectives of this contribution were to describe and quantify the reproductive traits that make up the viable sperm production of a population. Some of these reproductive traits were easily measured from wild fish (e.g., mature testes weight), and others were more easily measured on captive fish (e.g., fertilization potential and sperm motility). Results of laboratory and field studies were then integrated to generate estimates of viable sperm production of a fish stock. A number of experimental protocols have been employed over the years to assess male fertility. The strengths and weaknesses of the different experimental approaches were reviewed and appropriate recommendations given towards establishing standardized protocols. Although the review is broad in nature, and includes references to a number of marine fishes, it concentrated on exploited species that occur in the North Atlantic and Baltic Sea within the taxonomic groups gadoidae, pleuronectoidae and clupeidae (Clupeiformes). In addition, published data on male reproductive traits of species in these taxa were tabulated and summarized. The terms of interest included sex ratio, maturity state, testes weight, sperm fertilization potential (artificial fertilization and paired mating), sperm density, sperm motility and paternal effects on early life history traits.

An equation for determinate spawners was described that quantifies a population's viable sperm production using data on adult body characteristics and associated quantity and quality of sperm. The equation was used to establish time series of viable sperm production for Atlantic cod (Gadus morhua) of Newfoundland and Labrador. Results indicated on average1 600billion viable sperm were released to produce one recruit at age 3 years but with substantial variation among years in relation to changes in stock composition and growth as well as stock size. Distinct peaks in the number of viable sperm in 1981 and 1986 corresponded to distinct peaks in the number of age 3 recruits in those same years.