ABSTRACT
Groups of St Peter's fish Sarotherodon galilaeus were trained during 28 days of classical conditioning to respond to an acoustic signal by approaching a feeder. Their ability to retain the acoustically conditioned behaviour was tested after eight different intervals ranging from 12 to 188 days from termination of training. Retention tests comprised 7 consecutive days of retraining and the fish response was compared with that of naive fish. Fish response drastically diminished with time. After 55 days, there was no apparent expression of memory on the first test day but fish response was restored on subsequent retraining days, indicating the existence of latent memory. Six months from the end of training, there was no indication of behavioural retention and the response completely vanished. The study was conducted in the context of sea ranching, with classical conditioning used to gain control over fish location. In light of the present results, it is suggested that periodic reinforcement of the acoustically conditioned behaviour should be used.
Subject(s)
Acoustics , Conditioning, Classical/physiology , Retention, Psychology/physiology , Tilapia/physiology , Animals , Behavior, Animal/physiology , CuesABSTRACT
Intersex individuals, possessing both male and female genital openings, were assessed in two groups-7 and 19 months old-of Australian red claw crayfish (Cherax quadricarinatus). All intersex individuals investigated were functional males, as suggested by their malelike morphology and the presence of testes, sperm ducts, androgenic glands, and viable spermatozoa. When an ovary was present in an intersex individual from either group, the gonadosomatic index, the diameter of the oocytes, and the ovarian cytosolic polypeptide profile were similar to those of immature, pre-vitellogenic females. We conclude that intersexuality in C. quadricarinatus does not indicate a case of protandric sequential hermaphroditism, as previously suggested. The case of intersexuality described here presents a unique model for the study of the role of the androgenic gland in the regulation of sex differentiation in crustaceans.
ABSTRACT
For four months we marked and followed through female maturation and adult male mophotypic differentiation, the growth of all 150 individuals in an experimental population of Malaysian giant freshwater prawns (Macrobrachium rosenbergii). Small immature female prawns had high growth rates. Growth of female prawns nearly ceased after maturation. This compensatory growth process produces adult females having a unimodal, symmetrical size distribution with a mean above the size threshold for maturation (about 18-26 g). The small male morphotype has a low growth rate, while the orange claw male morphotype has a high growth rate. As the orange claw males transform to the blue claw morphotype, growth ceases. Examination of changes in size rank during the maturation process supported the leapfrog phenomenon. The fastest growing, largest orange claw male is the first to metamorphose to the blue claw morphotype (at a size of 35 g). As other orange claw males exceed this size, they transform in a sequential process so that the most recent blue claw male is generally the largest blue claw male in the population. Thus, growth of males is depensatory throughout the process of morphotypic differentiation, leading to a wide size range of orange and blue claw males. The leapfrog phenomenon is discussed in terms of the reproductive success of the blue claw males and compared with related growth processes in male poeciliid fishes. Implications of this growth process for aquacultural productivity includes the stimulatory effect on the remaining prawns of selectively harvesting the largest blue claw and orange claw prawns and suggests that the inclusion of a small proportion of large "target" blue claw males might stimulate the rapid growth of orange claw males in a population of smaller prawns.
