Studies on Improvement of Seed Production Techniques in Salmonids and Osmerids

Abstract

Anadromous salmonids and osmerids are artificially propagated in Japan by release of their seeds. However, there are many unsolved problems in the techniques of their propagation. In the present monograph, studies on the improvement of seed production techniques in 4 fishes (masu salmon Oncorhynchus masou, chum salmon O. keta, shishamo smelt Spirinchus lanceolatus and Japanese smelt Hypomesus nipponensis) were outlined. Techniques to evaluate dorsal fin pigmentation during smoltification as an external seed quality, and to improve seed quality of hatchery-reared fish, and the discovery of metabolic problems in hatchery-reared fish were described in yearling masu salmon. In underyearling masu salmon, techniques to evaluate nutritional conditions using kidney melano-macrophage density was developed, and applied to the evaluation of the nutritional condition in hatchery-reared fish after release. In chum salmon fry, the development of techniques to monitor the physical condition and to find its appropriate culture conditions was reviewed. In egg cultures of shishamo and Japanese smelt, techniques to eliminate egg adhesiveness with treatments of kaolin or scallop shell powder suspension were established in order to improve hatching rates. In addition, the appropriate embryogenetic stage for the release of shishamo smelt embryos was demonstrated. Consequently, this monograph reveals that these techniques contribute directly to the development of artificial propagation in some salmonids and osmerids. 1. General introduction Anadromous salmonids and osmerids including masu salmon Oncorhynchus masou, chum salmon O. keta, shishamo smelt Spirinchus lanceolatus and Japanese smelt Hypomesus nipponensis are important species for coastal and freshwater commercial fisheries in Hokkaido, the northern-most prefecture in Japan. These fish are not always abundant under natural reproduction systems (Nagata and Kaeriyama 2004; Torao 2005a, b; Miyakoshi 2006). Therefore, these fish are artificially propagated by releasing their seeds in order to increase their stock in various places in Hokkaido (Kusuda and Teranishi 1996; Kaeriyama 1999; Torisawa 1999). Masu salmon, which inhabit both Pacific Ocean and the Japan Sea coasts of Hokkaido, spawn in upstream regions in autumn and hatch the winter of the same year (Kato 1991). The fish are separated into two types: 104 S. Mizuno / Aqua-BioSci. Monogr. 5: 103–143, 2012 doi:10.5047/absm.2012.00504.0103 © 2012 TERRAPUB, Tokyo. All rights reserved. words, masu salmon propagation costs more money compared to chum salmon propagation. It is essential for the sustainable artificial propagation of masu salmon to reduce the cost of seed production by increasing the survival rate of seed. Hatchery masu salmon are released in two ways. One is called the smolt release method where yearling (1+) smoltified juveniles are released into downstream regions in spring, and the other is called the spring juvenile release method, where underyearling (0+) juveniles are released into upstream regions in spring (Mayama 1992). One of the keys to increasing survival rate of seed is stocking hatchery juveniles with high seed qualities determined from ethological, physiological and biochemical characteristics. However, seed quality of hatchery juveniles has not been perfectly evaluated in masu salmon. In addition, there has been no attempt to improve the seed quality of hatchery juveniles. Chum salmon, which inhabit the whole region of Hokkaido, hatch in rivers in winter, and migrate to the ocean the following spring. All of the fish are anadromous. After 2 to 6 years of marine life, adults return to spawn in their natal rivers in autumn (Salo 1991). In the program, 0+ fry, which were produced in hatcheries in the same way as the masu salmon, are released into the river in spring (Kobayashi 1980). However, the increased stock due to the propagationprogram has caused downsizing and aging (Kaeriyama and Edpaline 2004). This phenomenon is believed to be due to a population density-dependent effect: the growth of chum salmon fry is restrained by carrying capacity, such as the amount of food or habitat size, in the North Pacific (Kaeriyama et al. 2007). Hatchery fish have to coexist with wild fish in a narrow carrying capacity. Therefore, biological interactions between hatchery populations and wild populations are being studied (Kaeriyama and Edpaline 2004). Hilborn (1992) has warned that the excessive release of hatchery fish decreases the genetic diversity of Pacific salmon, including chum salmon. Accordingly, artificial propagation and the preservation of wild populations must be jointly considered in order to preserve the natural balance. Kaeriyama (2002) was concerned about the infection of wild fish by hatchery fish diseases. Considering this background, the reliable production of hatchery fry with good physical conditions is more important than an increased number of released hatchery fry for the sustainable artificial propagation of chum salmon. Chum salmon fry are intensively cultured in high density conditions in hatchery ponds. In general, intensively cultured fish are commonly under high physiological stress resulting from deteriorated rearing conditions (Patinõ et al. 1986; Papoutsoglou et al. 1987). On the other hand, it has been impossible to monitor the physical conditions of hatchery fry cultured in high density conditions, and practical environmental conditions for the culture of fry in good physical conditions have not yet been found. Shishamo smelt migrate to their natal river on the Pacific Ocean side of Hokkaido in early winter to spawn (Hikita 1930, 1958). Adults spawn 1.4 mm sized eggs in freshwater environments about 3 to 9 km upstream from the estuary (Ito 1959, 1963, 1964; Okada and Sasaki 1960; Okada et al. 1975, 1976; Omi 1978b). The larvae migrate to the estuary immediately after hatching carried by the snow-melt water during the following spring, and mature after 2 or 3 years of life in the ocean (Omi 1978a). All of the fish are anadromous (Miyaji et al. 1976). On the other hand, Japanese smelt, which are distributed around the whole of Hokkaido, consist of anadromous and lake-resident types (Hamada 1961; Katayama et al . 1999). Anadromous-type fish migrate to their natal stream and spawn 0.8 mm sized eggs in shallow streams from April to June (Shiraishi 1961; Torisawa 1999). The general lifespan of the fish is 1 to 2 years (Utoh and Sakazaki 1983, 1984, 1987; Torisawa 1999). For the artificial propagation of shishamo and Japanese smelt, larvae, obtained by artificial insemination, are released into the rivers or lakes through the drainage of hatchery waters (Iwai and Osama 1986; Kusuda and Teranishi 1996; Izuka 2003; Kitsukawa et al. 2003). However, the efficiency of the propagation has not yet been accurately evaluated. It is necessary to first produce a lot of seed to perform a pilot release, in order to establish effective seed-release methods and to elucidate the effects of releasing hatchery seed. Some shishamo and Japanese smelt hatcheries intensively culture eggs using upwelling flow-type acrylic and cylindrical jar incubators (Kusuda and Teranishi 1996; Kitsukawa et al. 2006). However, it was found that eggs cultured in the jar incubators showed low hatching rates (Takeda et al. 2002). In a few shishamo smelt hatcheries, eyed-stage embryos are released into the river (Mizuno et al. 2004b, 2005) before they hatch. However, the most appropriate time for releasing eyedstage embryos into the river is unknown. In this monograph, I review research performed on the improvement of seed production techniques in salmonids and osmerids, with the aim to solve some of the problems mentioned above. In Section 2, three approaches to evaluating and improving the seed quality of hatchery masu salmon smolt are described. Section 3 reviews 2 studies on the development and application of techniques evaluating seed quality in hatchery masu salmon parr for spring juvenile release. Section 4 deals with 2 studies dealing with the establishment of techniques to monitor physical conditions and the elucidation of appropriate culture conditions in chum salmon fry. In Section 5, three attempts to develop techniques to improve survival rate in artificial propagation of shishamo and Japanese smelt were deS. Mizuno / Aqua-BioSci. Monogr. 5: 103–143, 2012 105 doi:10.5047/absm.2012.00504.0103 © 2012 TERRAPUB, Tokyo. All rights reserved. scribed. The final chapter describes the implications and perspective studies of the improvement of seed production techniques in salmonids and osmerids. 2. Evaluation and improvement of seed qualities in 1+ hatchery masu salmon smolts