THE INFLUENCE OF TEMPERATURE DURING THE EMBRYONIC PERIOD ON LARVAL GROWTH AND DEVELOPMENT IN CARP, CYPRINUS CARPIO L., AND GRASS CARP, CTENOPHARYNGODON IDELLA (VAL.): THEORETICAL AND PRACTICAL ASPECTS
Department of Pond Fisheries, The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
ABSTRACT. This work proposes modifications to the existing system for identifying the steps of embryonic and larval development in fish. The term “compensatory phase of development” is proposed for the phase from hatching to the first intake of food. Both the new designations of these steps and the new name of this phase do not require a declaration of whether the hatched individual is considered to be an embryo or a larva, something that has been, to date, a matter of dispute. Unification will allow for the wider use of the new nomenclature, and make easier the comparison of results. This work examines the influence of the thermal history during the embryonic period (temperatures of 20, 24, 28, and 32°C) on later development, growth, and survival of common carp, Cyprinus carpio L., and grass carp, Ctenopharyngodon idella (Val.) larvae, at a constant temperature of 23°C. It was confirmed that the optimal temperature ranges for the embryonic development of common carp and grass carp are higher than those currently applied widely in practice of 18-22°C and 21-26°C, respectively. Based on the evaluation of the development, growth, and survival of the larvae, it was determined that the optimal temperature for embryonic development is 26-28°C for the common carp and 32°C for the grass carp. It was confirmed that even a short-term increase in temperature from 20°C to 24°C during the compensatory phase has a positive influence on subsequent common carp larvae growth.
Key words: EMBRYO, LARVA, EARLY DEVELOPMENT, ONTOGENY, TEMPERATURE, COMMON CARP, GRASS CARP
Michał Korwin-Kossakowski, The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Department of Pond Fisheries, Żabieniec, Główna 48, 05-500 Piaseczno, Poland, Tel./Fax: +48 (22) 7562088; e-mail: email@example.com
The first aim of the thesis was to attempt to systematize terminology referring to early fish ontogenesis based on an analysis of the literature and observations of the embryonic and larval development of common carp and grass carp (Table 2). Hatching fish are viewed by some researchers as embryos and by others as larvae. The use of these terms, which stems from varied approaches to early developmental biology, hampers communication and understanding among those writing on this topic. Depending on the convictions of the researcher describing it, the developmental phase following hatching is referred to variably as the “free embryo phase” or the “yolk-sac larva phase”. The current work proposes two changes that will enable the proponents of these two theories to apply one common system for describing ontogenesis. The disputed phase from hatching to the first exogenous feeding is referred to as the “compensatory phase of development” (Figs. 1, 2). During this phase, the hatched individual, whose state of development varies depending on the influence of environmental conditions, must achieve locomotor independence by the inflation of the swim bladder with gas. Next, it must achieve a developmental state that permits it to attain energy independence, which means consuming and digesting exogenous food. Thus, regardless of its initial state, the individual must reach the subsequent crucial point after hatching through its own development. The term “compensatory phase of development” does not describe whether the individual is an embryo or a larva, which means that it is acceptable to proponents of either theory. The second important modification regards the division of the embryonic (E1-E9) and larval (L1-L6) steps, which have long been in use and are still used currently (Peňáz 2001). The present work proposes to supplement the names of the steps after hatching, considered in this division to be embryonal (E), with symbols referring to larval development (L). This means that if hatching occurred at step E8 (as in common carp), the subsequent step would be referred to as E9/L0. If, however, hatching occurred at step E7 (as in grass carp), then the subsequent step would be referred to as E8/L0, and the next as E9/L01. The names of later steps, which refer to larvae, would remain unchanged (Table 15). This modification would allow disseminating this clear and convenient division that has been in use for many years, while also making easier the comparison of results described by proponents of various approaches to the concepts of “embryo” and “larva”.
The second aim of the thesis was to attempt to verify if the temperature during early ontogenesis (from fertilization to the first exogenous feeding) influences subsequent growth and development. The development of common carp and grass carp was studied at four temperatures (20, 24, 28, and 32°C), and then further development, growth, and survival were studied at the common temperature of 23°C. It was confirmed that the duration of development (ô) was shortened at higher temperatures (Tables 3, 5 and Fig. 3). It was also observed that increased temperature hastened embryonic development more in grass carp (Table 4 and Fig. 5) than it did in common carp (Table 6 and Fig. 6). As reported in the literature, the equalization of differences in hatched larva length during the compensatory phase of development was confirmed in both species (Tables 7, 8). Temperature during early ontogeny was confirmed to have an influence on subsequent growth and development during rearing at a common temperature of 23°C (Tables 9, 10). It was also confirmed that by applying various temperatures during the early ontogenesis of grass carp (from 20°C to 32°C), it is possible, at the same moment following fertilization, to obtain larvae that are nearly fourfold larger, at weights of 27.72 and 105.99 mg, respectively (Table 11). Using the duration of the compensatory phase of development and survival and growth (Fig. 7), the temperatures during early ontogenesis which are the optimal for subsequent rearing of the larvae of both species were determined. The optimal temperature for later common carp growth was 26-28°C during early ontogenesis, while the most appropriate of the studied temperatures for grass carp was 32°C (Fig. 8)