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More than 40 species of lampreys (Petromyzontiformes) are known worldwide. Some of them are parasitic and feed on the blood of fish or other aquatic animals. Lampreys spawn once in their lifetime, after which they die. One of the representatives of the ichthyofauna of European rivers is the river lamprey, Lampetra fluviatilis. The river lamprey is now an endangered species due to loss and degradation of their habitats. The present study investigated gonadal development without hormonal stimulation in female river lampreys during puberty under controlled conditions for a period of seven months. Female river lampreys were kept in conditions that mimicked the natural environment. During the November–May period, samples were taken monthly to determine the extent of gonadal development and gastrointestinal and liver changes using histological examination. From the results obtained, the dynamical changes were determined for the following: gonadosomatic index (GSI; %), hepatosomatic index (his; %), and digestivesomatic index (DSI; %). With the gonadal development of female lampreys, an increase in GSI (7–23%; November–May) and a decrease in DSI (0.4–0.1%; November–May) histological changes were observed in the gonads (oocyte development), intestines (over time, decreased lipid vacuoles and enterocyte apoptosis), and in the liver (decreased lipid vacuoles and hepatocyte apoptosis over time) and in the digestive system resulting from its degradation. Also, it was observed that there was a change in the color of the liver to green in April. This study demonstrated the key role of the liver in the oocyte maturation process in this species.

Successful propagation of fish depends on many factors including the optimal administration routes and delivery vehicles of spawning agents. In our experiments, the effects of different routes of administration and delivery vehicles of Ovopel (mammalian GnRH-analouge and metoclopramide) on ovulation were compared in African catfish (Clarias gariepinus). Seven females per treatment were used (BW = 606–1088 g). In experiment 1, fish in treatment 1 and 2 were given intramuscular (IM) and intraperitoneal injections (IP) of Ovopel suspended in fish physiological saline, respectively. For treatment 3 and 4, Ovopel was suspended in fish physiological saline (NaCl) and fish sperm (SP), respectively. The suspensions were introduced into the ovary of the females by a catheter. In experiment 2 (verification or clarification experiment), two treatments were administrated identically as experiment 1 for IM and SP. As a new treatment (SI) sperm was introduced into the ovary by a catheter, the Ovopel were administrated intramusculary. In both experiments, all females ovulated in all treatment groups. The relative number of stripped eggs was also similar among treatments within experimental cycles. Hatching rate was significantly lower for treatments where fish sperm was introduced to the ovary by a catheter whether it contained Ovopel (39.1 ± 18.3 %; SP, experiment 1 and 35.1 ± 21.2 %; SP, experiment 2.) or not (SI: 46.0 ± 9.2 %). While in other treatments, hatching rates were significantly higher and varied between 55.1 ± 16.1 % (IM), 66.7 ± 9.3 % (IP), and 63.4 ± 9.0 % (NaCl) in experiment 1 and 61.9 ± 12.0 % (IM) in experiment 2. The result of ovarian lavage with hormone preparations in saline have shown that the effects this novel method do not differ from the effects of reproduction with the use of traditionally injection by needle.

Growth patterns during early development of four species of riverine cyprinids, common dace (Leuciscus leuciscus L.), ide (Leuciscus idus L.), chub (Squalius cephalus L.) and common barbel (Barbus barbus L.), over 30 days of rearing, were analyzed. The study period covered three successive phases of larval development (preflexion, flexion, postflexion) and part of the juvenile development. The growth analysis carried out in the present study shows that significant allometric growth occurred mainly in preferentially localized body parts (head and tail) and was also associated with an increase in body height. The replacement of temporary structures (e.g., fin fold absorption) and the appearance of definitive structures around 21 mm TL (beginning of the juvenile period) corresponds to a stabilization of the relative growth of most parts of the body. This is probably due to the fact that the studied species had completed the most important part of the remodeling process (metamorphosis) and had achieved a body shape that allows juveniles to colonize faster water habitats. The results also indicate that individuals of species that are less developmentally advanced at the time of hatching (common barbel, chub) show greater initial dynamics of change in growth rate than individuals of species whose individuals are more advanced in ontogeny (common dace, ide). In addition, the small differences observed in growth parameters between successive periods analyzed, supported by the results of previous studies on these species, probably reflect the lack of abrupt changes in the behavior and habitat of the species studied.

Controlled indoor reproduction of European eel is commonly recognized as a prospective tool to prevent extinction of this fish species. There is a little information about diversity of bacterial microflora of European eel during long maturation under controlled but changing thermal and salinity conditions. Characteristics of the composition of the bacterial microflora inhabiting the body surface of fish kept firstly in fresh and then in salt water, may help enhance the survival of spawners and spawning efficiency. Knowledge about the presence of potentially pathogenic bacterial species and their antibiotic resistance is particularly important. Methods: This study analyzed the bacterial microflora of two types of necrotic changes on the skin of eel females during artificial maturation under fresh and saltwater conditions. Results: A total of two hundred and forty bacterial strains were isolated from necrotic dermal changes on fish in freshwater and saltwater conditions. Both the bacterial number and biodiversity were greater in freshwater than in saltwater. Psychrophilic bacterial strains in freshwater were twice as abundant as in saltwater, especially among isolates which were cultured from the mucus or from ulcerative changes around the chip injection point (up to 1010 cfu/mL). 16 S ribosomal RNA gene sequencing of isolates from the freshwater conditions revealed the presence of twenty genera of bacteria, including: Pseudomonas sp., Comamonas sp., Escherichia sp., Aeromonas sp., Citrobacter sp., Burkholderia sp., Pantoea sp., Enterobacter sp., Yersinia sp., Edwardsiella sp., Serratia sp., Bordetella sp., Morganella sp. and Chromobacterium sp. In saltwater conditions, five genera of bacteria were found dominantly: Pseudomonas sp., Aeromonas sp., Yersinia sp., Vibrio sp., Edwardsiella sp. In freshwater conditions, the bacteria were mostly resistant or resistant to all tested antimicrobial drugs. Conclusions: Changes in bacterial microflora during controlled indoor reproduction of European eel predispose fish to bacterial infection especially during the first freshwater step of female maturation. New, alternative to antibiotic therapy, methods should be adopted to prevent infections and enhance spawning efficiency.

The maraena whitefish, Coregonus maraena (Bloch, 1779), is often considered a suitable candidate for intensive aquaculture diversification in the EU. However, only a few such farms in Europe are in operation. Rearing this species in recirculating aquaculture systems is a recent innovation, and optimisation is necessary to standardise aspects of larviculture. This 30-day study investigated the effect of stocking densities of 25/L, 50/L, 100/L, and 200/L on the survival and growth of maraena whitefish larvae in a recirculating aquaculture system. The four groups of larvae (initial weight = 7.4 ± 0.1 mg; initial total length = 13.0 ± 0.1 mm) in three repetitions were reared in a recirculating system. Larvae were fed fresh live brine shrimp metanauplii every 3 h at a rate converted to larval stocking density. After the experiment, 10 larvae from each tank (30 of each density group) were weighed on a digital microbalance (ABJ 220-4M KERN, Germany, readout = 0.1 mg) and measured manually on images taken with Leica MZ16 A stereomicroscope and a digital colour camera with 5-megapixel resolution for Leica DFC420 Image Analysis. No significant differences in final body weight, total length, size heterogeneity, condition factor, or survival were found among treatments (P > 0.05). The highest non-significant survival rate and growth parameters were observed in larvae reared at 25/L. On the contrary, it is possible to rear maraena whitefish larvae at high stocking density without any subsequent negative consequences for growth and survival. As no significant differences in any evaluated parameter were observed between groups of larvae at the highest and lowest stocking density, we conclude that it is possible to rear maraena whitefish larvae at high stocking density (and 200/L) without any subsequent negative consequences for growth and survival.

Farmed fish and shrimp are continuously challenged by multiple stressors during their life stages, such as hypoxia, pH fluctuations, different salinities, high nitrite, un-ionized ammonia, injury during handling, inadequate nutrition, or food shortage, which can eventually adversely impact their health, welfare, and growth rates. Besides, these stressors can weaken production and decrease their resistance to diseases. Scientists and researchers have been making concerted efforts to find new, safe, and inexpensive supplements to mitigate the negative influences of stressors and thereby enhance the productivity of farmed aquatic animals. Some microalgae are microscopic unicellular organisms that were found to be promising feed supplements due to their richness in important nutrients such as minerals and vitamins. Moreover, some microalgae contain several bioactive phytochemicals that exhibit anti-inflammatory, antioxidant, and immunomodulatory properties. Several field-controlled studies provided evidence that using microalgae as feed supplements led to improved growth, physiological functions, immunity, antioxidant capacity, and disease resistance in farmed finfish and shellfish species. This review article emphasizes the beneficial role of the cyanobacterium Arthrospira platensis and seven microalgal species, including Chlorella vulgaris, Parietochloris incisa, Dunaliella salina, Aurantiochytrium sp., Haematococcus pluvialis, Tetraselmis sp., and Nannochloropsis oculata in mitigating stress effects in farmed finfish and shellfish species. The conclusions of this article throw light on the potential benefits of using microorganisms in aquaculture.

This study aimed to determine the dietary effects of honeybee pollen (BP) on growth parameters, intestinal microbiota, hepatic histoarchitecture, and intestinal histomorphometry of African catfish Clarias gariepinus juveniles. The feeding experiment was carried out in a recirculating aquaculture system under controlled conditions for 21 days to achieve more than a 10-fold increase in weight in fish from the control group. Fish were fed well-balanced commercial feed without any supplements and served as a reference group (group C) and other diets enriched with varying BP levels as 1% (BP1), 2% (BP2), and 3% (BP3). Results showed a significant (p < 0.05) effect of the dietary BP not only on the growth parameters (such as final body weight: 5.0 g to 6.6–7.5 g, weight gain: 0.23 g/d to 0.31–0.35 g/d, body length: 84.7 mm to 93.8–95.9 mm, and specific growth rate: 11.7%/d to 13.1–13.7%/d, group C vs. experimental groups, respectively) but also on the development of beneficially important gut microbiota, such as lactic acid-producing bacteria. In BP-enriched groups, an average of 45% higher body weight gain was observed compared to those reared in the control group. The histological analysis showed that dietary BP may have a positive effect on the development of the intestinal tract and may enhance the absorption of nutrients with the potential ability to maintain a normal hepatic histoarchitecture of the treated African catfish. The results obtained suggest the optimum level of BP additive to feed for African catfish should be 1%.

One of the finfish species that European and North American breeders are most interested in is the northern pike, Esox lucius. Artificial reproduction and the production of viable larvae has a huge impact on further culture. The quality of stripped gametes is highly variable. Therefore, it is important to use gametes with maximum efficiency, which has a direct impact on the amount of stocking material produced and therefore on the economics of production. The aim of this study was to compare northern pike fertilization efficiency, expressed as the survival rate of embryos until hatching. In the first experiment, the highest percentage of hatched embryos was observed in groups of eggs fertilized in a saline diluent prepared with deionized water (after reverse osmosis: group D), at 61.2% and 56.5% in the NaCl5-D and NaCl6-D groups, respectively. The highest percentage of hatched embryos in the second experiment was observed in the egg groups activated with Woynarovich solution (V) at 75.5% and 74.7% for V-D (D—deionized water) and V-T (T—tap water), respectively. In all cases, preparing the activation medium using T versus D water resulted in lower fertilization percentages and lower percentages of hatched larvae. At the same time, two variants (V and B1—Billard solution) were tested during mass spawning in three hatcheries using hatchery water (tap water). The results showed that repeatability was the highest when using activation medium B1.

This study analysed the effect of feeding a freshwater fish, barbel (Barbus barbus), with Artemia sp. enriched with polyunsaturated fatty acids (PUFA). Barbel larvae were divided into two groups, which received a daily dose of nauplii at 50 % of the fish body weight. One of the groups received nauplii enriched with PUFAs (group E), whereas the other received nauplii without enrichment and was used as a control group (group C). After 21 days of feeding with Artemia, the fish were switched to artificial feed. The second stage of the experiment lasted 28 days. Supplementation Artemia with PUFA improved the growth and feed utilisation indices. The mortality rate in group E was lower than in group C, although the differences were not statistically significant. Histological analyses revealed better development of the active area of intestines, as well as an increase in the neutrophil count in the blood. The fatty acid profile changed: the percentage of EPA and DHA increased. Use of Artemia enriched in PUFA in barbel rearing protocol proved to be an effective method of improving the effects of culturing the larvae.

This study determined the contents of cadmium (Cd) in the muscles, ovaries, and eggs of silver female European eels. The analysis of cadmium content was performed on female European eels caught during commercial fishing in freshwater in Warmia and Mazury (Poland), and then subjected to artificial maturation and ovulation processing under controlled conditions. The content of cadmium (Cd) in the tissues was determined by flameless atomic spectrometry using an electrothermal atomizer. The analysis showed statistically significant differences between the cadmium content in the muscles, ovaries, and eggs (p < 0.05) of female European eels. The lowest cadmium content was found in the muscle tissue (0.0012 ± 0.0001 mg kg−1 wet weight) and the highest in eggs (after ovulation) (0.0038 ± 0.0007 mg kg−1 wet weight). Moreover, a relationship was found between the cadmium content in the muscle tissue and the ovaries (R = 0.673; p = 0.0117) in the same fish. The movement of cadmium from tissues to oocytes may indicate a significant problem concerning this heavy metal content in the reproduction of European eel.

This experiment analysed the operation of submerged and dripping biological filters with three types of filling: commercial fitting HXF12KLL (CF), two innovative polypropylene aggregates (PPA) and polyethylene screw caps for PET bottles (PSC). The experiment determined the time needed to reach full filter functionality at the maturation stage, the time needed to start successive stages of the nitrification process and the maximum concentration of each nitrogen compound in water in the recirculation systems. The filter operation characteristics after the maturation stage were also examined. These issues are crucial during the preparation and launch of new aquaculture facilities. A literature analysis indicated that the ability of biological filters to oxidise nitrogen compounds is affected by a number of factors. Studies conducted at various centres have covered selected aspects and factors affecting the effectiveness of biological filters. During this study, the model fish common carp (Cyprinus carpio) was used. The current experiment involved examination of biological filter maturation and operation during the carp fry rearing stage, which allowed the biofilter operation characteristics to be determined. At the third day of the experiment, the ammonium concentration reached approximately 3 mg NH4-N/dm3. It remained at this level for 10 days and later decreased below 0.25 mg NH4-N/dm3. The maximum nitrite concentration ranged from 11.7 mg/dm3 to 20.9 mg NO2-N/dm3 within 9 to 20 days and later decreased with time. Nitrate concentrations were seen to increase during the experiment. The all applied biofilter media showed possibility to be used in commercial aquaculture systems.

The European eel Anguilla anguilla is a highly important market species which is also increasingly in danger of extinction in Europe. One of the ways of protecting the species in the natural environment, while maintaining its market supply, is its aquaculture, e.g. due to much higher survival rate under controlled conditions than in the wild. However, this can be done only when an effective artificial reproduction biotechnique is developed. The aim of this study was to use an ultrasound device to determine the sex and to perform a biopsy of the gonads, which is a part of complete protocol of eel artificial reproduction. The findings indicate that ultrasonography is highly useful in determining the sex in migrating eel (100% of sureness) and in performing high-precision biopsy of the gonads. The present method gives the possibility to quick determine the maturity of the female gonads. The application of ultrasonography (USG) is totally safe for fish and a portable ultrasound device can be used in both the laboratory and in the field.

This study demonstrated that individual fecundity of 34 migrating European female eels Anguilla anguilla increases linearly with body weight (BW) and total length (TL). The total individual fecundity of fish from 560 to 1960 g BW was between 981 x 103 and 6320 x 103 eggs, respectively. The mean relative individual fecundity equalled 2415 x 103 (± 524 x 103) per kg BW. The values of this parameter ranged from 1753 x 103 to 3224.5 x 103 kg–1. Based on the results, it might be suggested that A. anguilla has lower total individual fecundity than New Zealand longfin eel (Anguilla dieffenbachii), American eel (Anguilla rostrata) and Japanese eel (Anguilla japonica) although it has one of the highest fecundity values per kg BW. Total fecundity was strongly depended from fat level in muscle (R2 = 0.9523) and ovary (R2 = 0.9531) as well as level of DHA content in ovary (R2 = 0.8967) and muscle (R2 = 0.6274) (N=10). There were no important relationship between total fecundity and protein level as well as in muscle and ovary

The eel is a catadromous fish which spends most of its life in freshwater and adults swim to the Sargasso Sea region to spawn. While preparing for the reproductive process, eels undergo a metamorphosis to become what is called silver eel; a process involving changes in the colour and weight of the body and an increase in the eye size. These are indicators of fish maturity and they facilitate the selection of fish for reproduction under controlled conditions. During this study, changes in the body weight (BW) and eye size in female European eel were observed while being given weekly hormonal injections of 20 mg kg–1 carp pituitary homogenate and kept in 15°C freshwater and in 15°C saltwater with a salinity of 32-33‰. Fish kept in saltwater but not subjected to hormonal stimulation were used as a control group. Furthermore, after the experiment was finished, females in the control group were kept for next 5 months, with the same environmental parameters maintained. Differences between the treated groups were observed as early as week 4 of the experiment. An increase in fish BW was observed in fish kept both in salt and freshwater which were subjected to hormonal stimulation. On the other hand, changes in eye size were observed in the fish kept in saltwater, both in those hormonally stimulated and otherwise. The eye diameter in the fish kept in fresh after hormonal stimulation did not change significantly.

This study presents artificial induction using tench eggs, Tinca tinca (L.), of androgenetic origin. The oocytes taken from common bream, Abramis brama (L.) and common carp, Cyprinus carpio L. were genetically inactivated using UV irradiation and then inseminated using tench spermatozoa. Androgenetic origin (haploid or diploid embryos) was checked using a recessive colour (blond) and morphological markers. The percentage of hatched embryos in all experimental groups was much lower than in the control groups. All haploid embryos showed morphological abnormalities, which were recorded as haploid syndrome (stunted body, poorly formed retina, etc.). The optimal dose of UV irradiation of common bream and common carp eggs was 3456 J m–2. At this dose, almost 100% of haploid embryos were produced at a hatching rate of over 6%. Lower UV-ray doses affected abnormal embryo development. The highest yield of tench androgenesis (about 2%) was noted when eggs were exposed to thermal shock 30 min after egg activation.

The aim of this study was to evaluate a procedure of weighing live fish larvae and to determine its impact on the survival and growth rates based on the example of ide Leuciscus idus(L.). The platform with larvae was then dried on the blotting paper and next weighed together with larvae. The weight of the larvae was calculated by deducting the weight of the platform from the total weight recorded. After weighing, the fish were returned to the rearing tank. Fish from the control group were not manipulated during the whole experiment. No significant differences were recorded in larvae survival, weight and length (91.33±4.73%; 41.69±10.70 mg; 17.56±1.44 mm and 94.00±4.00%; 49.40±10.79 mg; 18.41±1.24 mm in E group and C group, respectively). Significant differences were recorded in case of SGR that reached 15.80±0.29 in C group and 14.60±0.17 in E group. The described method may be a useful tool for determining fish larvae weight. Although it requires conducting further researches in order to establish the influence of accompanying factor such as e.g. kind and concentration of anaesthetic.

The aim of this study was to determine the effect of age of female ide on spawning success under controlled conditions. All ide breeders were collected from one wild population. Data concerning reproductive parameters were collected during induced spawning under hatchery conditions. The age of mature females ranged from 4 (average weight 504 g) to 9 years (average weight 2540 g) and the youngest collected females (3+) (average weight 330 g) were immature. The females from group 4+ produced smaller oocytes (1.28 mm diameter after hydration) than older fish (1.44-1.57). There were no differences in oocyte sizes in females 6+ and older. The highest relative fecundity (mean 44,621 eggs kg-1) was noted for fish aged from 5 to 7. Eggs obtained from the oldest females had the lowest biological quality: the highest percentage of dead embryos during incubation (49.9) and the highest percentage of morphological abnormalities in hatched larvae (5.6%). In addition, in the group of the oldest females, only 67% of fish produced eggs.

In this study the effect of six activating buffers on the movement parameters of sperm was determined and short-term storage of semen in TLP buffer was attempted (0.292g NaCl; 0.012g KCl; 0.011g CaCl2; 0.004g MgCl2; 0.105g NaHCO3; 0.002g NaH2PO4; 50ml; pH 8.6). Sperm was collected from five orfe individual, and spermiation was stimulated by means of an intraperitoneal Ovopel injection. The basic parameters of spermatozoa motility were measured after the semen was diluted with six different activating solutions, previously used successfully in other fish species. The motility analysis was conducted on a Crismas apparatus. Additionally, short-term storage of semen in TLP buffer was attempted. Subsequently, motility parameters were verified after 0 (Control), 24 and 120 h of storage at 4°C. It has been found that Lahnsteiner’s buffer (100 mM NaCl, 10 mM Tris, 0.5% albumin, 199 mOsmkg-1) was found to be the most effective in sperm activation. In this paper, the spermatozoa motility of colourful ide is indicated for the first time. Finally, there was a successful attempt at short-term sperm storage for five days. For artificial insemination, it is very important to select the most effective solution to stimulate sperm motility. Data regarding sperm manipulation of orfe are scarce, so the aim of the study was to determine the basic sperm quality parameters of the colour ide form, i.e. Leuciscus idus aberr orfus.

The aim of this study was to evaluate the suitability of females for artificial reproduction of common tench based on an analysis of the size and percentage share of oocytes sampled in vivo. The females were collected from natural waters (lakes) during the spawning season, After catching, the selected fish were transported to the hatchery, where the fish were kept under controlled conditions and oocytes were collected from all females. It was found that sampled oocytes were different in size and developmental stages. Oocytes were classified into 3 groups: small, medium and large. The diameter intervals for each group were 0.18-0.22 mm, 0.48-0.57 mm and 0.95-1.01 mm, respectively. Analysis of the percentage of the largest oocytes showed that their numbers decreased in time from over 40% on Day 1 to slightly over 10% on Day 10. A positive correlation was found between the percentage of the largest oocytes in the cathetered egg sample and the weight of the stripped eggs during artificial reproduction. The percentage of the largest oocytes (diameter 0.95-1.01 mm) might be used as an indicator of the possibility of reproducing wild tench. No statistical differences were observed in latency time and embryo survival of females showing different quantities of the largest oocytes.

Two forms of ide Leuciscus idus (L.) spawners: wild-coloured and ornamental: yellow-coloured were kept at three various temperature regimes shortly before spawning at optimal temperature regimes (group 1), under natural temperature conditions (group 2) and in rapidly increasing temperature (group 3). The quality and quantity of collected semen, ovulation rate and survival rate of embryos to the eyed-egg-stage were recorded. The quality of semen from group 3 (where the temperature increased over the thermal spawning optimum) was the worst (46 and 51% motility of spermatozoa for the wild-coloured and yellow form, respectively). The quantity of collected semen also was the lowest in the same groups (1.1 and 1.0 cm3 kg-1 for the wild-coloured and yellow form, respectively). Increasing the temperature to 16°C also caused a decreasing percentage of ovulated females (70% and 60% of ovulation for wild-coloured and yellow form, respectively) and biological quality of eggs (48.9 and 47.8% embryo survival for wild-coloured and yellow form, respectively). Fluctuations of temperature at a level of 8-14°C (group 2) did not negatively affect spawning results, except for a longer latency time (over 44 hrs). The results suggest that the temperature regime shortly before controlled reproduction of ide plays an important role influencing reproductive success.

This study was aimed at determining the effect of stocking density on growth, survival and development of asp Aspius aspius (L.), ide Leuciscus idus (L.) and chub Leuciscus cephalus (L.) larvae, reared under laboratory conditions. Fish larvae were obtained during artificial reproduction. The larvae were fed ad libitum with freshly hatched Artemia sp. nauplii. Eight density variants from 50 to 400 individuals per 1 L (at the interval of 50 individuals L–1) were tested. The initial rearing was carried out for 21 days at 25°C in a recirculation system especially designed for that purpose consisting of 16 tanks with a capacity of 1 L each. The fastest growth rate for all three species, expressed as the greatest average total length, weight and most advanced ontogenetic stage at the end of the experiment was obtained at the lowest stocking density. Fish from other treatments, particularly at densities exceeding 150 individuals L–1, were characterized by similar body sizes and the same ontogenetic stage on the last day of rearing. The recorded differences in the length of larvae among treatments became visible during the first (asp) or third (chub, ide) week of rearing. No effects of stocking density on larval mortality were found during the experiment.

In the current paper we present a method of rearing tench (Tinca tinca L.) larvae under controlled conditions, fed on dry food (Gemma and Perla) and Artemia nauplii or decapsulated cysts of Artemia. Tench larvae were obtained after artificial spawning by aid of Ovopel stimulation. Two experiments were conducted during which fish were divided into 4 groups (in duplicate) and placed in 30 dm3 glass fish tanks set up in a recirculating system. The fish were fed ad libitum and reared for 25 days. Larvae were fed exclusively (experiment 1) or after 10 days (experiment 2) of receiving Artemia nauplii with two types of compound feeds and decapsulated cysts of Artemia. The best growth rate was observed in the control group fed on Artemia nauplii and in the group offered decapsulated cysts in both experiments. The highest survival rate, over 96%, occurred in the control group. A twofold worse survival rate was obtained in the group fed exclusively on dry food. Applied transition schedule had significant effect on survival rate among treatments, however it did not influence the percentage of body deformations occurring in groups receiving compound feed only. The results obtained indicate the necessity of applying gradual transition from live food to compound feed and the improvement of feeding schedules in common tench culture.

In the current paper we present a method of rearing tench (Tinca tinca L.) larvae under controlled conditions, fed on dry food (Gemma and Perla) and Artemia nauplii or decapsulated cysts of Artemia. Tench larvae were obtained after artificial spawning by aid of Ovopel stimulation. Two experiments were conducted during which fish were divided into 4 groups (in duplicate) and placed in 30 dm3 glass fish tanks set up in a recirculating system. The fish were fed ad libitum and reared for 25 days. Larvae were fed exclusively (experiment 1) or after 10 days (experiment 2) of receiving Artemia nauplii with two types of compound feeds and decapsulated cysts of Artemia. The best growth rate was observed in the control group fed on Artemia nauplii and in the group offered decapsulated cysts in both experiments. The highest survival rate, over 96%, occurred in the control group. A twofold worse survival rate was obtained in the group fed exclusively on dry food. Applied transition schedule had significant effect on survival rate among treatments, however it did not influence the percentage of body deformations occurring in groups receiving compound feed only. The results obtained indicate the necessity of applying gradual transition from live food to compound feed and the improvement of feeding schedules in common tench culture.

Morphological development and allometric growth of laboratory reared Nannacara anomala were studied from hatching to the loss of larval characters and beginning of squamation (18 days post-hatching) at 26°C. The mean total length (TL) of larvae and juveniles increased from 3.74 mm at hatching to 9.60 mm at metamorphosis. Morphogenesis and differentiation were most intense during the first week of development. During this period (TL interval = 3.74 - 4.84 mm) there was an evident priority to enhance the feeding and swimming capabilities by promoting accelerated growth in the head and tail regions. Following this period, there was a major decrease in growth coefficients, indicating a change in growth priorities. Observations on the early development of Nannacara anomala confirmed the basic uniformity development of a substrate brooding cichlid.