Chapter 16: Reproduction
Laurence W. Crim and Brian D. Glebe
A vast and fast-growing body of literature documents our interest in fish reproduction. It also reveals a need to better understand the appropriate means of producing young fish of high quality. Methods to control and manage fish reproduction are diverse; they include storing gametes, changing fish gender, manipulating the timing of reproduction, and sterilizing fish. In this chapter, which deals with teleost fishes, we present ways to determine reproductive status and to manage or manipulate various aspects of reproduction; reproductive behavior is treated in Chapter 17. Our emphasis is on cultured species, for which the most reproductive information exists. We have been highly selective in our citations of published papers for this chapter, and we hope readers will consult the broader literature to gain a fuller understanding of reproductive physiology.
Dead fish can be sexed easily by direct examination of the gonads; Guerrero and Shelton (1974) described a method for sexing juveniles from gonad squashes. There is strong interest, however, in developing rapid and practical methods of sexing live fish. Such methods would lead to improved estimates of stock reproductive potential, more efficient feeding and marketing of domesticated stocks, and more efficient sample sizes for sex-specific experiments, among other advantages.
Live juvenile fish are especially difficult to sex because they usually lack external features associated with sexual maturation, such as breeding tubercles or sexually dimorphic pigment patterns and urogenital pores. Even the adults of some species such as milkfish lack consistent, perceptible differences in external body characteristics. Reliable sex determinations for such fish presently must be based on direct examination of the gonads or by blood or mucus tests.
Noninvasive methods to sex live fish from gonads promise speed and convenience but they still are under development. For example, although Martin et al. (1983) used commercial ultrasonic instruments to sex mature coho salmon, imaging technology still cannot discriminate the gender of juveniles reliably.