Atlas of abnormalities in gametogenies and early life stages of sturgeons

Harald Rosenthal

• Verlag: Books on Demand
• Jahr: 2015
• ISBN drucken: 9783739257754
• eBook-ISBN: 9783739259451
• Auflage: 1
• Thema: Betriebswirtschaft
• Thema: Business allgemein

The Society intends to act as an international forum of scientific discussion for all persons interested in pertinent issues on sturgeons while at the same time seeking opportunities for close co-operation at an international level.The vision for this society is to see stocks thriving once again in important sturgeon waters in the basins of Caspian, Asov, Black, North and Baltic seas, rivers in Siberia and China as well as in the Great Lakes region of the United States and Canada in addition to other North American watersheds. The Society therefore hopes through its activities to enhance the understanding of species protection world?wide and across na1onal borders in regions with different cultural and political backgrounds (using the highly endangered sturgeons as case examples) in order to foster the sustainable use of natural resources that are traded globally.

1. Introduction

1.1 Brief history of sturgeon fishery decline and conservation in Russia

Accounts on the history of sturgeon populations in the Caspian Sea and elsewhere have been extensively reported (Korobochkina, 1964; Khodorevskaya et al., 2009; Lukyanenko, 1999; Pourkazemi, 2006; Rosenthal, et al., 2006; Ruban and Khodoresvskaya, 2011). A drastic decline in the abundance of sturgeon populations occurred during the last decades of the 20^th century. This was caused by a complex array of interacting factors. The most detrimental causes that gradually and increasingly threatened the populations world-wide and particularly around the Caspian Sea, were (a) the increasing fragmentation of rivers by the construction of hydroelectric power dams, the interruption of migrating routes of spawners to the upstream spawning sites, (b) inefficient management of the fisheries, (c) increased illegal catches, and (d) water pollution (Raspopov, 1992; Veshchev, 1991 a,b; 1998; Khodorevskaya & Novikova, 1995; Vlasenko, 1997; Krasikov, Fedin, 1998; Novikova, 1992; Ruban, 1999; Ivanov, 2000; Novikova & Khodorevskaya 2000; Khodorevskaya et al., 1997; 2001; 2002; 2009; Veshchev, 2000; Khodorevskaya, 2002). An abrupt decrease in abundance of most sturgeon populations practically necessitated a general banning of commercial fisheries in Russia and, in some cases, listing of certain species and populations in the RF Red Data Book and the endangered species inventories of the federal administrative entities.

In the late 1950s and early 1960s a rapid decline in natural reproduction of Caspian sturgeons was associated with the reduction in available spawning grounds of the Volga River. This has led to develop controlled breeding and to establish hatcheries producing large quantities of larvae and juveniles for release. Subsequently, hatcheries also became important to maintain sturgeon populations in other rivers and basins (e.g. Ob River, Yenisei River, and Baikal Lake).

In recent years, sturgeon culture has been used as principal tool to provide juveniles for release to maintain valuable sturgeon stocks (Khodorevskaya, 1999; Barannikova et al., 2000; Kornienko, 2000). It has been shown that controlled reproduction and release of progeny into the Volga-Caspian basin accounted for about 99% of Beluga (Huso huso, Linnaeus 1758) catches, 56% of Russian sturgeon (Acipenser gueldenstaedtii, Brandt and Ratzeburg, 1833) recruits, and 36% of Stellate sturgeon (Acipenser stellatus, Pallas 1771) recruits (Khodorevskaya et al., 2000). However, releasing programmes were drastically reduced in recent years, partly due to the absence of suitable spawners (Barannikova et al., 1994; Dovgopol and Ozeryanskaya, 1994; Zhuravleva, 2000; Khodorevskaja et al., 2007). In the case of Stellate sturgeon, catches of spawners caught in the wild and exploited at hatcheries in the Volga Delta showed a tendency towards lower ratios of ovulated females that can be obtained after hormonal stimulation. These ratios declined from 64-67.7 % in 1993-1994 to 47.5 % in 1995. In the Volga River, males (3 %) and females (28 %) of Stellate sturgeon revealed abnormal gametogenesis. An increase in diversity of these abnormalities was also registered in the hiemal groups of the Volga Russian sturgeons at the beginning of upstream migration (Saenko, 2000). One may argue that besides environmental effects on reproductive capacity, there may also be a problem with “outbreeding depression”, thus indicating an effect that fits well with Seleye’s (1952) adaptation syndrome where responses to environmental stressors (e.g unnatural culture environments) may have its significance in higher levels of integration (e.g. performance at the reproductive level of the next generation). However, at the time where stellate sturgeon showed this type of effect, 96-98 % of the Beluga females still produced high quality eggs (Kamolikova and Kokoza, 1997).

1.2 The need for global cooperation on sturgeon conservation

Over the past decades the status of most sturgeon species has considerably worthened despite various efforts in many regions. There is need to increase our efforts including international cross-border cooperation in order to save these species:

• Considering the continued decline of many of the sturgeon species to crisis level,
• noting the limited number of experts working in the field of sturgeon conservation, and
• recognizing that man-made impacts are still increasing with massive negative effects on these highly endangered species,

we wish to reiterate the basic statements made in the “Ramsar Declaration on Global Sturgeon Conservation” (Rosenthal, et al., 2006), pointing to the needs of immediate and long-term commitments (time horizon 30-50 years) to regain self-sustaining populations. It is strongly recommended to join forces across borders and share experiences and concepts in support of adequate national and international research to guide management adequately within the limited time frame available for recovery.

It is for this reason that the World Sturgeon Conservation Society was established in 2003 with the aim to (a) foster the conservation of sturgeon species and restoration of sturgeon stocks world-wide, (b) to support the information exchange among all interested in sturgeons, and (c) to enhance cooperation between fisheries, science, local administration and governmental agencies while also (d) to dissimminate scientific information on conservation issues through high quality publications and conferences. The present publication is exactly serving this purpose.

1.3 New approaches in sturgeon conservation culture

The efficiency of controlled reproduction depends on numerous factors such as the quality of gametes of parental fish and on the adequate incubation and rearing methodologies to obtain healthy and viable fry. According to numerous data, sturgeons from various basins demonstrate a wide range of abnormalities in development and functioning of the reproductive system that directly influences the egg quality and the capacity of embryos for survival in the natural environment (Dettlaff et al., 1981; Faleeva, 1987; Romanov, 1990; Romanov & Altuf’ev, 1990, 1992; Romanov et al., 1990; Romanov and Sheveleva, 1993; Akimova and Ruban, 1992, 1996; Shatunovsky et al., 1996).

While we recognize that some of these abnormalities and malformations must be related to environmental deterioration, it is difficult to correlate these observations to particular environmental stressors or pollutants, mainly because of lack of quantifying data. At the same time, these malformations at embryonal and larval stages can also be caused by suboptimal culture conditions. For example, embryonic malformations have been used in biological effects monitoring programmes to quantify contaminant body burden of gonads with the intensity of embryo malformations in North Sea commercial fish species (Westernhagen et al, 1981; Cameron et al, 1992; Dethlefsen et al, 1996). Therefore, to assess the quality of methods to produce healthy and viable eggs and progeny is a matter of high importance. There is a future need to employ a more standardized investigational protocol for sturgeons. Unfortunately, this type of standardization has not yet been done. Once these protocols are in place, the use of developmental abnormalities as biological indicator in the reproductive system can become more meaningful, particularly if these can be quantified at cohorts or population level. It has to be noted that any organism responds to any stressor by a limited number of compensatory mechanisms which have been highly successful in evolution (Seleye, 1952). Effects may, therefore, be very similar regardless of the stressor while the intensity may be factor-specific, depending on the exposure concentrations.

There is a wealth of literature on the bioassay and biological effects monitoring that will have to be considered in the future. The concept behind the idea to use biological effects to assess environmental stress is based on the so-called “Seleye`s adaptation syndrome” (Seleye, 1952), indicating that any effect observed in one stage of ontogenetic development (gamete, biochemistry of the cell, early and late embryos, larva, juvenile, adult, cohort and population) will have its causes in the levels below and its integrative effects in the levels above (Rosenthal and Alderdice, 1976). For example when observing a malformation (e.g. microphthalmia) in an embryo shortly before hatching, the cause of this malformation may have occurred at the stage of differentiation of the eye tissue when the egg may have temporarily been exposed to low oxygen level in an incubator (too tightly surrounded by other eggs). However, the significance of this effect is expressed at later stages of development (e.g. first feeding stage, impaired vision and lack of precision in hunting for food items). The concept on the direct link between environmental stressors...

Inhaltsverzeichnis

• Epigraph
• Table of Contents
• 1. Introduction
• 2. Materials and methods
• 3. Structural abnormalities in gonads and gametes (Appendix I, II and III)
• 4. Structural abnormalities in sturgeon larvae (Appendix IV)
• 5. Structural abnormalities in juvenile sturgeons (Appendix V)
• 6. Discussion
• 7. References
• Appendix I - Abnormalities in structure of ripe oocytes in sturgeons from Volga-Caspian basin and aquaculture broodstocks
• Appendix II - Abnormalities in egg structure of Siberian sturgeons during the different periods of gametogenesis found in natural populations
• Appendix III - Abnormalities in the structure of sturgeon testes
• Appendix IV - Structural abnormalities in sturgeon larvae of the Volga-Caspian basin and in aquaculture
• Appendix V - Abnormalities in sturgeon juveniles from the Volga-Caspian basin and from aquaculture
• Copyright