Production and predation rates in a cannibalistic Arctic char (Salvelinus alpinus L.) population

Abstract – Production of cannibalistic Arctic char ( Salvelinus alpinus (L.)) and their prey conspecifics were estimated in an allopatric population, situated in an alpine ultraoligotrophic lake in central Norway. Estimates of population abundance were obtained by mark recapture and successive removal experiments. Assuming stable age distribution, we estimated mean yearly biomass (±95% CL) of char in sampled size groups vulnerable to predation (60 to 150 mm) to 7.93 (5.11–14.30) kg · ha⁻¹. Similarly, mean yearly biomass (±95% CL) of cannibalistic char (> 250 mm) was estimated to 0.62 (0.50–1.06) kg · ha⁻¹. Annual production (±95% CL) of char in length groups 60 to 150 mm was estimated to be 4.31 (2.74–8.03) kg · ha⁻¹ · year⁻¹, and production (±95% CL) of cannibalistic char to 0.19 (0.15–0.33) kg · ha⁻¹ · year⁻¹. Depending on the food conversion factor (set to vary from 0.1 to 0.4), the cannibalistic char removed from 10% to 40% of the production of char in sampled size-classes vulnerable to predation yearly. The overall ecological efficiency in energy transfer between the prey and predator population was 4.4%.     

Do cannibalistic fish possess an intrinsic higher growth capacity than others? A case study in the Asian redtail catfish Hemibagrus nemurus (Valenciennes, 1840)

This study relied on the day‐by‐day analysis of bioenergetics and prey size preference in larvae and juveniles of Hemibagrus nemurus selected at random, held in isolation (28.5°C, 12L:12D) and feeding ad libitum on conspecifics [21 fish, 12–46 mm total length (TL), dry mass (DM) of 1–145 mg]. Several traits concur to make young H. nemurus highly cannibalistic: (1) high predation capacities (largest prey = 88% and 70% TL in fish of 8 and >40 mm TL, respectively), (2) opportunistic feeding behaviours with no marked size preference and (3) an unusual combination of high food intake (>100% DM at 1 mg DM) and very high gross conversion efficiency (>0.70). A growth model was constructed from the top performances of fish feeding maximally (16 of 21 fish) and indicated that the risk of cannibalism would be high and permanent except for meal frequencies over five daily meals. Cannibals emerging spontaneously under communal rearing (6 fish L^?1, three daily meals) grew more slowly or just at the same rate as predicted by the growth model constructed from siblings selected at random. This indicates that the individuals that become cannibals do not possess higher intrinsic capacities for growth than others.     

Using attraction to light to decrease cannibalism and increase fry production in guppy (Poecilia reticulata Peters) hatcheries. II: the effects of light and cannibalistic adults

Predation of newborn fish by cannibalistic adults is a major cause of fry loss in guppy breeding tanks. The efficacy of using light to attract newborn guppies into a safe area, thereby reducing the cannibalism rate, was evaluated in aquaria. The aquaria were divided using small‐mesh netting into a section with adult fish and a safe section without adults, above which a light source was installed to attract the newborns. Both, the presence of cannibalistic adults and the light, increased the number of newborns in the safe section. The effect of the cannibals was pronounced during the day, and the effect of light seemed to be more pronounced at night. The presence of light significantly decreased cannibalism rate after 30 min, but not 16 h after the introduction of newborns. When tested with cannibalistic adults that have not been fed for 5 days prior to testing, cannibalism rate was higher and the effect of light on reducing cannibalism was evident both 30 min and 16 h after the introduction of newborns. The results demonstrated the potential efficacy of using white light in reducing cannibalism and increasing fry yields in guppy hatcheries.     

Bioenergetics of cannibalism in juvenile barramundi Lates calcarifer (Bloch): exploring growth advantage of fish fed live prey and formulated diet

The present study investigated the growth performance of juvenile barramundi Lates calcarifer (Bloch) fed conspecific prey (CP), formulated diet (FD) and a mix of both (MIX) using a bioenergetics approach. Fish in the MIX treatment ingested significantly more CP than FD by dry mass. However, prey mass ingestion and cannibalism rate in the MIX treatment were significantly lower than in the CP treatment. This indicates that the provision of alternative food does not complete mitigate cannibalism, but it can significantly reduce cannibalism in barramundi. Fish in the FD treatment showed a significantly higher daily food intake than fish in the CP or MIX treatments. However, fish fed conspecifics showed significantly better feed conversion efficiencies, apparent digestibility rates and growth performances. Exclusive cannibalistic barramundi assimilated significantly more energy consumed, with 1.5% of energy lost in faeces comparing with 7.3% of siblings feeding exclusively on FD. Consequently, exclusive cannibals channelized more energy consumption into growth (57.1%) than those fed solely on FD (43.9%). Therefore, high energy allocation into growth promoted better feed conversion efficiency and growth performance of cannibalistic barramundi than siblings fed solely on FDs. This study implies that fast‐growing cannibals may continuously prey on slow‐growing conspecifics due to growth advantage through cannibalism. Therefore, size heterogeneity should be reduced at initial stocking and controlled as fish grow to avoid the emergence of new cannibals.     

大口鲇苗种同类相残的研究

在不同条件下，对大口鲇苗种（全长1．07－9．43cm)进行同类相残研究，结果表明，饵料缺乏时的相残率均显著地高于饵料充足时（P＜0．01，N＝8），放养密度对大口鲇苗种的相残行为有影响，大口鲇苗种相残最严重的时期是在平均全长1．07－2．68cm阶段，当平均全长达6．71cm以上时，相残行为较弱，苗种间个体大小存在差异，尤其是大规格苗种间出现个体大小差异时，相残行为较严重，饵料缺乏是导致大口钻苗种发生同类相残的主要原因，高放养密度和个体大小的差异会诱发和促进同类相残的发生。     

大黄鱼人工育苗研究

1998年5月，从福建购得大黄鱼（Pseudoxciaena crocea）受精卵200万粒，经10h充氧运输，获上浮好卵150万粒，次日孵出仔鱼120万尾。在水温18－22℃条件下，经40d培育，育出2cm鱼苗38万尾，成活率32％。鱼苗从1.2cm开始互相残食，是前期减量的主要原因，应加强轮虫、卤虫的营养强化，以避免营养缺乏性。     

Dynamics of intracohort cannibalism in cultured fish

Abstract Cannibalism is a frequent phenomenon in fish, especially in culture environments where fish are unable to escape predation via habitat segregation or migration. Not all cultured fish species start to exhibit cannibalism at the same age or size, nor is cannibalism equally intense in different species or life stages. Predator to prey size ratios vary substantially between species and life stages, chiefly because cannibalism is governed by gape size limitations and allometric growth of mouthparts. The development of sense organs, hard body parts, swimming and escape capacities in both the predator and the prey also influence prey size selectivity. The dynamics of cannibalism are influenced by these, as well as by environmental, factors that have effects on feed intake, growth depensation and facilitate or complicate the displaying of cannibalistic behaviour. Knowledge about cannibalistic behaviour and the logistics of cannibalism along with environmental enhancement are prerequisites for the mitigation of cannibalism in aquaculture. Also, within the context of strain selection, it is of importance to determine whether cannibals are natural‐born killers or just lottery winners. These factors are discussed, chiefly as they apply to intracohort cannibalism. In addition, guidelines are suggested for cannibalistic risk assessment, and methods for mitigation of cannibalism are discussed.     

Food and feeding habits of ribbonfish Trichiurus lepturus in coastal waters of south-western Taiwan

ABSTRACT:   The catch of ribbonfish Trichiurus lepturus in the coastal waters of south-western Taiwan has significantly declined in recent years. To examine the effects of exploitation on the feeding habits of ribbonfish, 1570 specimens were collected on a monthly basis during March 2002–March 2003 from the landings by trawlers operating in the coastal waters of south-western Taiwan. The size of the ribbonfish ranged from 83–298 mm preanal length (PL), with a peak at 201–250 mm PL. Although they fed on shrimps and squid, fishes including Benthosema pterotum , Bregmaceros lanceolatus and Encrasicholina heteroloba were their main food items . In particular, B. pterotum was the most important food all year except during summer. No evidence of cannibalism was found in this study. No differences between day and night were found in the feeding activity of T. lepturus . However, B. pterotum and Acetes intermedius were the most important prey in the daytime, whereas B. lanceolatus , B. pterotum and E. heteroloba were at night. Feeding activity and the number of food items increased with increasing size of ribbonfish. Their feeding intensity in February to June, the main spawning season, was significantly greater than in other months. Changes in the food and feeding habits of this species before and after the recent period of heavy exploitation are discussed in detail in this study.     

Onset and development of aggressive behavior in the early life stage of Japanese flounder

Onset and development, and diel rhythm of aggressive behavior were observed in the early life stages of Japanese flounder Paralichthys olivaceus . The frequency of nip was counted as an index of aggressive behavior. No aggressive behavior was observed during the larval stage until day 39 after hatching (when fish were 13.2 mm in standard length (SL)) in the experimental tanks. The onset of aggressive behavior was observed on day 39, coinciding with completion of metamorphosis from the larval to the juvenile stage, and it developed until day 46. During the metamorphosing stage, typical shivering behavior (Ohm (Ω)-posture) was observed, and it showed a peak on day 19 (SL 7.6 mm) and decreased thereafter. Ω-Posture disappeared in the juvenile stage. Aggressive behavior and Ω-posture were only observed in the daytime. Settlement was first observed from day 19 in less than 30% of larvae and all individuals settled from day 39. As Ω-posture was observed regardless of the presence or absence of food and the peak of frequency in Ω-posture was observed in a specific stage of metamorphosis, this behavior is not related to feeding behavior, and it is possibly a precursor to aggressive behavior in this species.