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Fish are widely used in numerous fields of basic and applied research. Currently, they are the third laboratory animal group in numbers, and will become increasingly important. Common carp is a major species in both aquaculture and research. Inbred strains of carp by gynogenetic (only female inheritance) and androgenetic (only male inheritance) reproduction techniques were developed at our university. With these methods, homozygous animals are produced in one generation and we present the production of homozygous inbred and F1 hybrid strains of common carp. As in mammalian research, using genetically well defined fish is a methodological necessity since in outbred stocks: (1) repeatability between experiments is low, (2) high levels of inbreeding may have accumulated and (3) high intrastrain variability might obscure treatment effects. Within inbred strains, the variation is reduced and as a result, less animals (compared to outbreds) are necessary to obtain statistically significant results. We illustrate this with experimental data from an F1 hybrid and partly outbred strain of common carp, both subjected to an antibiotic treatment resulting in reduced gonadal growth. Results obtained from a single inbred strain should be generalized with the use of a panel of inbred strains. We show that optimal allocation of animals between and within inbred strains depends on the ratio (variation between strains): (variation within strains). When selecting a panel of inbred strains, attention has to be paid to genetic relations between strains to avoid testing within a limited genetic range. It should be considered that in inbred strains, (genic) dominance and interaction effects are absent, due to the absence of heterozygous genotypes. In general, variation within inbred strains will be reduced for traits with a high degree of genetic determination. However, in inbred strains of carp produced by gynogenesis or androgenesis, the chromosome manipulation treatment induces considerable (environmental) variation. By using F1 hybrids of carp, derived from crossing homozygous clonal siblings this source of variation can be avoided. Still, variation in F1 hybrids of carp is relatively large and varies greatly between strains when compared to inbred strains of laboratory rodents. It is assumed that their poikilothermic nature makes them more susceptible to environmental variation. Using inbred fish lines will increase experimental quality and leads to a more efficient use of experimental animals.

The biology and population dynamics of Sardinella longiceps and S. fimbriata were studied around East Java, Indonesia. The total catch of Sardinella spp. in East Java was 56 000 tons in 1993, and more than 50% of this catch was landed by purse seiners. Samples of purse seine catches were taken from three landing sites around East Java, at the Madura Strait, the Bali Strait and at the Indian Ocean. Biological data were collected on a monthly basis, during a period of 2 years, from March 1990 to March 1992. Patterns in reproductive activity were determined on the basis of changes in geometric mean gonado-somatic index (GSI) of mature fish. Length-based methods were used to estimate growth and mortality. Peak catches of sardines from the Madura Strait and the Bali Strait were recorded at the beginning of the rainy season around November and December. The Indian Ocean produced peak catches during the dry season, from July through October. Considerable differences exist between monthly catches from peak seasons and monthly catches from off-seasons. Patterns in reproductive activity could be recorded for the fish from the Madura Strait and both species of Sardinella showed peak reproductive activity there around November and December. Both species were estimated to grow to lengths of around 12, 17 and 19 cm in their first, second and third year respectively. Based on the age structures in the catches from different sampling sites, in combination with the migration patterns of the fish, it was concluded that both S. longiceps and S. fimbriata stocks can be divided into northern and southern populations. The northern populations were sampled in the Madura Strait and were assumed to be from the Java Sea, Makassar Strait and/or Flores Sea. These stocks consist of three year classes and do not seem to be under excessive fishing pressure. The southern stocks, well known from the Bali Strait sardine fisheries, are concluded to be under very heavy fishing pressure. These stocks consist of only two year classes and hardly any fish reach the length of maturity. Regulations controlling fishing effort are needed urgently for these fisheries.

Pubertal female Clarias gariepinus (recipients) were exposed for 62 days to holding water from intact, completely castrated, seminal vesicles-extirpated or testes-extirpated adult male or from intact adult female conspecifics (donors). In operated male donor groups, levels of six androgens (measured by RIA) were lowest in testes-extirpaied and completely castrated males. However, even complete absence of the testes (GSI 0%) did not eliminate circulating androgens. Male holding water exerted primer pheromonal action in enhancing ovarian development of recipient females, irrespective of the male donor group. Holding water from female donors was ineffective, comparable to controls (fresh water). Thus, although the effect of holding water is linked to the male gender, the gonadal origin of ovarian growth-stimulating compounds in the holding water could not be demonstrated.

Stimulation and inhibition of gonadal development by intersexual contact was studied in pubertal African catfish, Clarias gariepinus. The effect of a possible interaction was studied by evaluation after a 98-day experimental period of gonadal development in combinations of intact and anosmic males and females. In addition, separate groups of males and females, respectively, were exposed to holding water from these combinations. A tentative model of stimulation of gonadal development by intersexual contact in pubertal fish was developed. Males stimulate ovarian development of females by both olfactory and tactile cues. In addition, males seem to enhance gonadal development of other males through olfactory stimulation via holding water. In contrast, females tended to inhibit male gonadal development, especially through tactile cues. It seems that although males are hampered by female tactile stimuli in their gonadal development and ability to stimulate male gonadal development, their ability to stimulate female gonadal development is not affected.

1. 1. Pubertal vitellogenic and previtellogenic female Clarias gariepinus were exposed to holding water from a mixed-sex population of adult conspecifics. 2. 2. Exposure to holding water caused an accelerated ovarian growth in both cases. 3. 3. Analysis of holding water by gas chromatography and mass spectrometry (GCMS) yielded the presence of several steroids and steroid glucuronides known to be produced in adult, prespawning C. gariepinus . 4. 4. The possible role of these compounds in stimulating ovarian growth is discussed in relation to earlier findings on their pheromonal properties.

Shrimp, Penaeus monodon (Fabricius) and Penaeus merguiensis (de Man), culture on East Java is described with special attention to the differences in production characteristics between areas and districts. Traditionally, tambak culture developed along the North coast of East Java where the majority of modern tambaks are still located. The practice never developed extensively on Madura's Island. With the exception of the latter, intensification, startingin 1984-1987, touched all areas. In 1991, the combined production of P monodon and P. merguiensis reached 35 000 Mt, representing a value of US$ 220 × 106. The following year, a decline in total production was noted, mainly caused by a diminished production of intensive farms. Possible causes for this production drop are explored.

Temporal and spatial patterns in the fishery for Sardinella spp. around East Java, Indonesia, were studied in an attempt to develop an efficient catch and effort sampling strategy for this highly variable fishery. The inter-annual and monthly variation in catch, effort and catch per unit of effort (cpue) are quantified and discussed, using official catch reports and reports from local village cooperatives. In 1993 the total catch of Sardinella spp. in East Java was 56 000 tonnes and the total effort was equivalent to 5000 units of purse seine. A maximum sustainable yield (MSY) of 40 000 tonnes of sardines is estimated, at an optimum effort of 3000 units of purse seine. The present study focuses on the purse seine fishery since this fishery accounts for more than 50% of all sardines landed in East Java. Purse seiners use lamps to attract fish and peak catches are landed around the new moon. Catches are smaller towards the full moon, when the fishery is inactive during a period of 10 days. Considerable differences exist between monthly catches from peak seasons and monthly catches from off-seasons. The fishery is further characterized by a relatively large amount of zero catches. A catch and effort data recording system (CEDRS) is developed based on the analysis of temporal variation in cpue and effort in the purse seine fishery for sardines. A purse seine fleet, with a variable size of 40 to 70 vessels, was sampled in Probolinggo harbour at the Madura Strait, during 4 to 6 days per month from March 1990 until March 1991. The overall mean effort of the fleet was 36.1 trips per day, of which on average 12.6 trips per day resulted in non-zero catches. The geometric mean cpue over the non-zero catches was 404 kg per trip. The proposed CEDRS has an accuracy of 30% for the estimated annual catch, 21% for the cpue and 9% for the effort (non-zero catches). A minimum required number of 4 sampling days per month is calculated for the temporally stratified CEDRS, with months used as strata within years, and lunar phases as strata within months. For this purpose, the lunar cycle is divided in three lunar phases, one around the full moon, one around half moon and one around the new moon. Within the proposed CEDRS, no sampling takes place in the lunar phase around full moon, when the fishery is inactive. The sample of 4 days per month is proportionally allocated over the other two lunar phases.

Adult female African catfish, Clarias gariepinus , were manipulated to enter the phase of ovarian recrudescence by induced ovulation and stripping. These females were exposed to various conspecific stimuli for 33 days. At the end of the experimental period, gonadosomatic indexes (GSIs) were higher in females which had received holding water from a mixed-sex population than in comparable controls. The effect was abolished when recipient females had been rendered anosmic, indicating the presence of chemical substances perceptible through olfaction. Fecundity estimates and histological analysis suggest that the increase in GSI due to pheromonal stimulation is caused by both an increased recruitment of oocytes into the stage of exogenous vitellogenesis and by an enhanced deposition of yolk material in the oocytes. It is concluded that male C. gariepinus release pheromones with a stimulatory effect on vitellogenesis. Neither anosmia itself nor metabolites in holding water affected ovarian recrudescence or body weight increase. The biological significance of such pheromones is discussed in the context of observations on reproduction of C. gariepinus made in the natural environment.

Ovarian growth in pubertal African catfish was followed during a 100-day period. Different combinations of male sensory stimuli resulted in three distinct levels of ovarian development. A basic level (ovarian weight 5.3–7.5 g; GSI 1.9–2.7%) was reached in controls (no contact with males) and in females having visual and auditory contact with males. An intermediate level (ovarian weight 11 g; GSI 4%) was reached if olfactory contact with males was possible. A maximum level (ovarian weight nearly 20 g; GSI 7.3%) resulted from unlimited contact between the two sexes. The question is discussed whether the difference between maximum and intermediate levels of ovarian growth should be ascribed to a better water quality due to experimental conditions rather than to the presence of male tactile stimuli. The possible existence of male primer pheromones responsible for the observed stimulation of ovarian growth in pubertal African catfish by enhancing vitellogenesis is also discussed.

A comparison was made between the fecundity of female African catfish, Clarias gariepinus, transferred from their natural habitat in Northern Israel to nearby fish ponds and an indoor hatchery respectively, and conspecifics reared and kept in an indoor hatchery in The Netherlands. The results indicate that an inherent endogenous rhythm rather than the natural light periodicity determines the cyclical changes in ovarian activity, and that this internal rhythm is determined by environmental factors at an early stage of development. High water temperatures and the presence of males seem to enhance ovarian activity and to shorten its resting period. The significance of gonadotropin secretion by the pituitary for the ovarian cycle is discussed. It is concluded that for propagation of C. gariepinus throughout the year, independent of the seasons, broodfish should be reared and kept in hatchery tanks at a water temperature of 25°C, with proper feeding, in the presence of males, and at any local light periodicity.

The relationships between Penaeus monodon production and three crop characteristics in 107 ponds on nine shrimp farms in East Java were studied. Overall differences of production (Mt ha-1 year-1), survival rate (%), stocking density (number m-2) and mean weight at harvest (g) between regions and between farms were significant, while the difference of production between farms was also significant within regions. Overall analysis revealed that production was positively correlated with survival rate, stocking density and mean weight at harvest, while there was a negative correlation between stocking density and survival rate. Results imply that more attention should be paid to improving shrimp survival. The higher on-farm production in South East Java is linked to higher survival rates and higher post-larvae stocking densities than in North West and North East Java, while similar individual weights at harvest to North West East Java are reached. In this context, the relationship between coastal estuarine water quality and yield needs further investigation. Other parameters which need further investigation are farm management, post-larvae origin and duration of the culture period.