Ewa Kamler

Developmental response of carp, Cyprinus carpio, larvae fed different foods or starved

SynopsisThe developmental interval, body length, dry and wet weight were determined in carp larvae during the first 2 weeks of exogenous feeding. Six feeding groups were reared at 26°C; four groups received different artificial diets, whereas zooplankton-fed larvae and unfed larvae served as controls. It was found that larval developmental rate can be modified by the type of food. The diet affects the relationship between developmental step and weight. The effect of diet on the relationship between development and length becomes manifest at older steps (after longer feeding the same diet). A threshold point, after which satisfactory results of feeding artificial diets to carp larvae can be expected, depends not only on body size but also on the degree of development.

Gravimetric techniques for measuring consumption of live foods and artificial diets by fish larvae

Abstract Three gravimetric techniques for measuring the consumption of various foods by carp larvae are presented. I — Evaluation of the consumption of very fine zooplankton (rotifers) by larvae was based on measurements of the changes in prey number; corrections were made for energy losses of rotifers. II — Assessment of the consumption of larger zooplankton (cladocerans) by larvae was based on measurements of changes in prey dry weight; corrections were made for prey mortality. III — Determination of the consumption of artificial diets (starters) was based on measurements of changes in starter dry weight; corrections were made for starter losses in water.

Endogenous feeding period

Yolk is the main energy source for most fishes during the endogenous feeding period,* which begins at fertilization (or any other triggering stimulus that begins cell division) and ends with the onset of exogenous feeding by the hatched larvae (Fe to S in Fig. 4.1). There is an obvious difference between the early development of fish and that of some other oviparous animals, such as invertebrates, reptiles and birds: the former hatch before their yolk is fully resorbed (H in Fig. 4.1).

Characteristics of fish reproductive products

The terms ‘strategy’ and ‘tactics’, both derived from military science, are useful in the analysis of fish reproductive processes (Wootton, 1984). Wootton considers reproductive strategy as a ‘overall pattern of reproduction typically shown by individuals in a species’; it consists of a complex of traits, e.g. age at first reproduction, fecundity and many others, including size and nature of gametes (Wootton, 1982, 1984). Although the original meaning of the terms strategy and tactics implied rational planning, this implication has no relevance to biological processes. The latter occur in variable environments; both the overall reproductive strategy and is tactical variations are adaptative. One approach to the study of such adaptive mechanisms is by analysing the relationships between traits of reproductive strategy and environmental variables.

Feeding of fish larvae in aquaculture

The main objectives of fish culture are to maximize survival and growth, which accordingly are measured to evaluate the effects of rearing technologies. Survival and growth are usually computed from samples taken at the beginning and at the end of the experimental period. These determinations are open to errors which may reduce the reliability of comparisons.

Mixed feeding period

A mixed feeding period can be defined as a time when yolk reserves are reduced and the larval fish must commence external feeding. Mixed feeding usually occurs between the initiation of external feeding and the complete resorption of the yolk sac.

Early exogenous feeding period

Balon (1986) proposed three life-history models for fishes: indirect, transitory and direct. Indirect ontogeny comprises five periods: embryo, larva, juvenile, adult and senescence. The transitory model has an alevin period as a vestige of the larval period. In the direct model the free embryo transforms directly into a juvenile. Balon (1986) showed that elimination of the larval period occurs in species producing few, but large, eggs; within such eggs (Section 4.1) incubation is prolonged. Hence, a shift along the r-K continuum (Pianka, 1974) in the K direction would be connected with an elimination of the larval period from fish life history.