Know the
Fish Eggs Holomorphology Egg
Types Collection Identification Dignosis
Introduction
Almost all marine bony fishes are oviparous and a few of them are ovoviviparous and viviparous. The egg number of oviparous fishes have great differences from small numbers of hundreds, such as salmon has hundreds, to three hundred millions as in ocean sunfishes. Fishes spawn few eggs that are generally demersal eggs, which usually are attached or adhered under the gravel or in the crack of rocky reefs. Fishes those spawn many eggs are normally floating type and either drift in the ocean or coastal area by the waves. Most of the parent fishes that spawned demersal eggs have the nesting behaviors, so the identification of species can be done by the parental nursery behavior of the adult fishes. But most of the pelagic eggs found in the marine waters are too difficult to identify the species.
In the past, identification of fish eggs is by recording their continuous morphological changes from eggs hatch to larval and to juvenile fishes then to adult fishes. Some of the fish eggs are collected from the field of oceans, rivers and some of them are from the fish hatcheries. To identify these fish eggs, optical microscope is used most of the time. Fish egg classification reports are available since the beginning of 19th century. Syosi (1924) provided a checklist of 53 pelagic eggs along the coastal areas of Japan. Prof. Mito(1960a, 1960b, 1966)described 200+ fish egg forms and published the atlas and checklist of fish eggs collected from the Kyushu area of Japan from 1951 onwards. Also there were 349 types of fish egg forms described in Okiyama (1988). The book An Atlas of the Early Stage Fishes in Japan is the best tool for the egg forms and retrieve information nowadays. For the past years, Japanese scientists use hatching methods to explain over 20 types of marine fish egg forms (Suzuki et al, 1981, 1996; Suauki & Kobayashi, 1989; Kazunori et al, 1982; Tanaka, 1995, Shukei et al, 1990; Jettrey & Moyer, 1985). In mainland China, Institute of South China Sea, Chinese Academy of Sciences: Xiamen University and Yellow Sea Research Institute have added the species composition of fish eggs into their ocean ecological survey in South, East, and Yellow China Sea. Chao & Chen (1985) published Fish Eggs and Larvae in the Offshore Waters of China which includes 100 types of fish eggs. Chiang(1997)and Hu & Chiang(1991)have identified, 40 families, 26 genus, and 36 species at the central and northern parts of Taiwan Strait. However, the lack of information relating to this aspect still exists.
For twenty years, SEM is used to observe tiny structure found on the egg membrane surface and also in the micropyle region (Riehl, 1982). Later, many research reports are published relating to this topic (Hosokawa 1985, Mikodina 1987, Riehl & Koscha 1993, Hirai 1993, Britz et al 1995, Breining and Britz 2000). In Taiwan, Chen et al, (1999) used micropyle ultrastructure to classify four species of sparids, eggs and infer their phylogeny. Wu(2000)and Shih(2002)also applied this method to identify lizardfish and parrotfish eggs but add molecular techniques, and suggested that only DNA sequence could identify the species level. Shao et al (2002) discussed the advantages and defects of optical microscope, SEM and DNA sequences, and suggested that the identification using morphological characters can only identify the family or genus level. Therefore, simply using altas or diagnostic keys for identification may lead to mistakes, and this is because the characters of fish eggs are not specific enough to species identity. Many closely related species possess the same morphological characters, so when referring to the altas or the diagnostic key, some of them may key to the species, but the same characters may also belong to the characters of other species or even to whole family or genus. Even use additional observation of SEM for ultrastructures it cannot guarantee the identification to the species level. The only way to confirm the species is using DNA sequence alignment.
Figure 1. shows the identification relations of these three methods. This reminds the readers, particularly to pay attention in advance for identification. That is when you check the form of fish eggs fitted in one of the species assigned in this book, you could only confirm it to the genus or family level, but not exactly belong to that particular species. On the other hand, the fish egg designated to that species in this book is certainly the morphology of that species. Furthermore, most of the identification in this book is according to the Alats of Okiyama (1998), Mito(1960a & 1960b) and Chao & Chang(1985)and so on. Some of the species are the first descriptions from our research in these years. It includes 22 species of fish eggs that are collected either from the known species from the fish hathery farm or from mouth-breeding cardinalfishes. The authors are responsible for allthe drawning and photos including the scanning electron microscope
Shao et al (2002), for the first time used the mitochondrial DNA sequence of fish egg and sequence alignment of known adult fishes to identify the species. This method is also used to reconfirm the identification made in the past using fish egg atlas or diagnostic keys. Due to high cost of molecular biology facilities and the technical difficulties, it is not so easy to establish the complete molecular data of all adult fishes. However, the adult fish sequence is needed in advance to compare with the eggs. At the same time, if proceeding with the investigation of DNA sequences, one must classify the fish eggs first in order to collect adult fish sample of that particular group (taxa) to build up the species DNA sequences database. In brief, the characters observed by optical and SEM could possibly identify the order, family, and genus level: each level of identification has its own values. As a result, publication of this book has both values in terms of academic research and use.
Generally fish eggs size is small, so people wont pay much attention. In the past, fish eggs are considered as one of the zooplankton without further identification. Nevertheless, fish egg contains many important information of fish life history and fish ecology. So it plays an important role in environmental impact assessment, fishery stock analysis, fish propagation, seedling release, and fish farming. Besides, fish eggs themselves are important prey item in whole marine food web. Therefore, the identification of fish egg is as important as fish larvae.
Old Egyptians began eating fish eggs in the year of 2500. Initially fish eggs are added with salt to lengthen their editable time. Later on fish eggs become the desktop munificent objects. Many people describe the taste of fish eggs as butter flavor, fruit flavor, or special dividual seawater smell, and they even dissolved instantly when put into the mouth. Because of the different nature of fish eggs, soft, lubricate, fragrant, brittle and delicious, people love to eat it very much. Some fish eggs are even wrapped in oil membrane, which results in the delicious juicy nature. Because of high nutrition, fish eggs become routine necessity for human beings in the form of caviar, fish egg sushi, fish egg salad, mullet roe etc. Those large-sized fish eggs like salmon, trout, flying fish, etc, and many economically important fish eggs such as mullet, sailfish, cero, etc. All of these fish eggs are eaten by people in the unripe form before spawning.
However, when people eat fish eggs, why dont they think that kill chicken to get eggs will totally obstruct the primary stage of fishs life cycle. This leads to population and resource decline drastically. Especially using weaved straw mat to collect flying fish eggs or catching fishes during their spawning migration which will leads to severe depletion of the stock, e.g. massive catch of mullet or catch groupers or croakers in their spawning aggregation. Poisoning, electric fishing and blast fishing, also have destructive effect to egg laying or hatching fishes.
Taiwanese people love to eat fresh seafood very much, but the bad habit of eating rare species, fish eggs, and larval fishes should be changed. The restoration of larvae and fish eggs is one of the key factors to keep the fish resources sustainable. The conservation research must contain the long-term monitoring of the species composition and their spatial and temporal distribution of fish eggs in the coastal waters around Taiwan. All of the delimitations of Marine Protected Areas search for breeding and spawning grounds should establish the basic distribution data for fish eggs and larvae. We believe that the publication of this guidebook should be very useful for the identification of fish eggs in the future.
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