Abstract: Background and Objective: Feed is a prerequisite for all forms of life. A study of the food and feeding habits of fish is very important in any fisheries research programme. If the experiment was under controlled condition, it was inevitable to know the feeding habits and food of the experimental fish. The ultimate aim was for the captive breeding and larval rearing of the fish. Thus, the objective behind the study was to understand the food preference of the adult and the young ones, there by culturing the preferred feeds under laboratory conditions. The live feed culture will open up a new way for aquaculture promotion. Materials and Methods: Monthly samples of Hypselobarbus kurali (H. kurali ) were collected from the fishes caught by local or traditional fishermen along the Kulathupuzha region of Kallada river system. Data were calculated by annual feeding index which is the ratio of the number of specimens whose feeding were either active or moderate to the total number of specimens examined during that year×100. Results: For the present study, it was observed to be Daphnia sp. represented the major diet of young fishes. The feed preference was also noted to be the Daphnids. Daphnia sp. alone was consumed by H. kurali up to the size of 90-109 mm size class and dominated in the food up to 120-29 mm size class. Thus, if these zooplanktons are mass cultured under laboratory condition, then it will be a boon to the fisheries sector and there by fresh water fish aquaculture. Conclusion: So the present study provides a clear idea about the feeding profile of H. kurali and opens a new virtue for culturing the species under captivity providing its preferred food.
INTRODUCTION
Captive breeding studies cannot get completed without knowing the feeding trend and status of the species which is going to be reared in captivity. Food and feeding of a species can be examined and studied in different steps. Information on food and feeding habits of fishes is essential for better understanding of their growth, breeding and migration. It was inevitable to have knowledge on natural diet of an animal which was required for the study of its nutritional requirements, its interaction with other organisms and its potential for culture1. The spectrum of prey consumed by a species helps to define its fundamental niche2 and its realized niche terms of interaction with co-habituating species. Understanding the food and feeding of an individual species add on to the possibilities of culturing the same under captivity3-8.
For the better management of fish stock, knowledge of food was inevitable as it forms the most important factor regulating or influencing the abundance, growth and migration of fishes. Several scientists have discussed the food of fishes in relation to sexual cycle, condition of feed, selectivity in feeding and drawn conclusions that bear upon the biology of the species concerned9-15.
For analyzing fish stomach contents, occurrence method, numerical method, point method, volumetric method and gravimetric method are widely used16-20. Hence, to study food and feeding habits of fishes, the method chosen must suit the diet of the fish to be studied. The most appropriate measure of dietary importance was the one where both the amount and bulk of a food category were recorded21. Pre-ponderance method22 takes into account the frequency of occurrence as well as bulk of food items that is the volume, providing a definite and measurable basis for grading different food items. As this method suits the carnivorous and omnivorous fishes, this method was used widely in investigations.
The present study will put light on transportation, artificial maintenance set up, water quality and food and feeding of H. kurali. Several steps in transportation methods were practiced and refined into an efficient and effective technique. The anesthetized fish transportation technique assured 100% success. Once the fishes were transported and brought to lab, its water quality maintenance and providing suitable system which complements its natural system became the prime important issue which needed immediate attention. The fishes thus acclimatized to the system were provided with feed. The feeding biology studies done in the fish helped in determining the most suitable food for the fishes.
MATERIALS AND METHODS
Monthly samples of H. kurali were collected from the fishes caught by local or traditional fishermen along the Kulathupuzha region of Kallada river system. After wiping the fishes in the lab each fish was measured to its total length and weight to the nearest mm and mg, respectively. After dissecting out the abdomen the fishes were examined for the sex, maturity stages and degree of fullness of stomachs. The variations in the fullness of fish stomach were classified as ‘gorged’, ‘¾ full’, ‘½full’, ‘¼full’, trace and empty. The stomachs of fishes were removed, weighed and preserved in 7% formalin for further analysis.
The index of preponderance method 22 was adopted here. The index of preponderance was worked out by:
where, Vi and Oi represents the percentage of volume and percentage of occurrence indices of each food item, respectively and I the index.
Food items of fishes were identified up to generic level. It was counted and measured volumetrically. All unidentifiable and partially digested food items were grouped under digested food remains. There was detritus as the major food constituent as the fish was omnivorous. For the analysis of fullness of stomachs, they were grouped into actively fed (gorged, full and ¾ full stomachs), moderately fed (½ full stomachs), poorly fed (¼ full stomach) and stomachs with traces of food or empty. A total of 180 specimens were randomly selected, comprising of 98 males measuring between 165-348 mm and 71 females measuring between 160-339 mm total length. Eleven juveniles measuring between 92-160 mm. TL (total length) were also used for the present study. Food analysis was done in relation to months, sexes, maturity stages and size groups. The fishes were classified with a class interval of 10 mm length groups.
Annual feeding index23 was calculated which is the ratio of the number of specimens whose feeding were either active or moderate to the total number of specimens examined during that year×100.
RESULTS
The list of food items occurred in the stomachs of H. kurali is given in Table 1. Analysis of stomach content showed that the food of H. kurali consists of two major components arthropods and detritus along with some negligible phytoplankton remnants.
| Table 1: | General diet composition of H. kurali |
| Table 2: | Index of preponderance values of different food items in the stomach of H. kurali
|
These two together formed 63.7% of the food (Table 2). Rotifers formed 25.29% whereas protozoans and miscellaneous together formed 11.01%. Among the total food item analyzed arthropods dominate in constitution by 55.91% of the diet. Among these, the major groups were crustaceans, copepods and cladocerans (39.74, 9.13 and 7.04%, respectively). Among crustaceans Daphnia sp., Siola sp., Daphanosoma sp. and Moina sp., were abundant. Among rotifers, Brachionus sp., dominated the most (17.00%) followed by Keratella sp., (5.31%) and the remaining unidentifiable rotifers (2.98%). Among miscellaneous items partly digested insect larvae, a fish head and some matters unidentifiable were present.
Daphnia sp., (crustaceans) was the most preferred food item in most of the months followed by Brachionus sp., (rotifers). Unidentified digested reminants were found plenty in certain months. Among protozoans, Chlamydomonas sp., Opalina sp., Vorticella sp., etc was found. Cyclops sp., (Copepods) was recorded during Diaptomus sp., was found. Zooplanktons other than Daphnia sp., was found only occasionally in the stomachs. While Bosmina sp., (arthropod) was observed in 6 months through out the study period. Tropocyclops sp., were recorded only for 2 months. Holopedium sp., Alonella sp., Sida sp., Macrothrix sp. and Latona sp., was recorded for the study. Calanoid sp., were found in the stomach for only 1 month. Mud and detritus were found in the food throughout the year, that also in a very well pronounced quantity (Table 3).
Juveniles preferred crustaceans as the major food item with an index value of 83 whereas in male and female the values were 29 and 22, respectively. The index value for detritus and mud was 13 for juveniles while in males and female which formed major component had index values of 69 and 74, respectively (Table 4).
Daphnia sp., alone was consumed by H. kurali up to the size of 90-109 mm size class (Table 4) and dominated in the food up to 120-129 mm size class. From 110-119 mm onwards, mud and detritus started dominating along with rotifers and protozoans, while rotifers were found dominant in 130-139 mm size class fishes. Insect larvae remnants in 200-209 mm size class and 240-249 mm size groups were found to have a mixed group of all zooplankton with no constant representatives. Mud and detritus along with arthropods were the only food item observed above 250 mm of H. kurali.
Daphnia sp., was the most favored food item in males of 160-199 mm length (Table 5). The index of preponderance values were 98.7, 69.4, 52.1 and 36.05 for 160-169, 170-179, 180-189 and 190-199 size groups, respectively. The index values for all crustaceans together, respectively were 99.8, 67.4, 53.6 and 39.5 from 210 mm onwards. Males of H. kurali fed on rotifers, protozoans, insect remnants, zooplankton mixtures, mud and detritus.
| Table 3: | Monthly index of preponderance of different food items of H. kurali pooled |
| Table 4: | Size wise index of preponderance of different food items of H. kurali |
| Table 5: | Index of preponderance of different food items in different size groups of male H. kurali |
| Table 6: | Index of preponderance of different food items in different size groups of female H. kurali |
The females fishes of 200-219 mm preferred Daphnia sp., and with growth the preference shifted to mud and detritus (Table 6). Crustaceans were an important diet in the size group from 160-199 mm. From 250 mm onwards the preference completely shifted to mud and detritus with mixtures of zooplanktons (rarely). Mud and detritus formed the chief food item in the size group ranging from 230-259 mm. The results showed that while smaller sized fishes prefer Daphnia sp., as the diet, larger ones feed exclusively on mud and detritus.
Hypselobarbus kurali quite often prey up on entire organisms and stomachs exclusively contained crustaceans, digested insect larvae, fish remnants, mud and detritus. The stomach often was gorged with detritus by 37.79% and arthropods representatives up to 55.91%.
DISCUSSION
Knowing the feeding habit of a fish is inevitable for breeding it in captivity. By studying the gut content of the fish at different size range and for male and female a clear image of the diet preference and feeding trend could be figured out. For the present study it was observed that the fishes of the lowest size range mostly preferred Daphnia sp. As the fish grows the preference shifted to rotifers and protozoans and ultimately to mud and detritus. It was simply evident from the list of feed composition that the fish is strictly omnivorous, among which the planktons dominated the most. Studies points that fishes such as Rutilus rutilus also feeds extremely on zooplankton24. Insect feeding was also noticed in other fishes like Wallago attu25.
The feeding intensity of fish was related to its stages of maturity, reproductive states and the availability of food items in the environment26. Live foods are able to swim in water column and are constantly available to fish and shellfish larvae are likely to stimulate larval feeding response. The small fingerlings, thus, studied in this study had showed minimal quantity and variety of feed and it may be due to the aforesaid reason. It was observed that for H. kurali juveniles preferred mostly the cladocerans. Studies revealed that the cichlids and cyprinids are zooplanktivorous when they are young. Rotifers, copepods, crustaceans and their nauplii were eated by O. mossambica less than 50 mm long27. About the same mixture of zooplankton is found in the stomach of S. galilara in a Nigerian pond28. Small specimens (11-21 mm) eat some phytoplankton also. The next stage of individuals shifted to zooplankton before yielding to an adult detritus feeding habit. The zooplanktivorous habit remains same in young marine detritivores29. The older fishes showed variation in feed composition and also quantity which also supports the statement of Ricker26.
As the growth progress, the preference was shifted to protozoans and rotifers and ultimately to detritus. The result was same with that of some cichlids. In O. mossambica as it grows the diet typically changes from one zooplankton to one composed of algae, diatoms, amorphous detritus and sometimes the leaves of macrophytes upon which periphyton grows30. The gradual transition of cyprinid larvae to a juvenile and then to an adult, studied in lake Lucia, Zululand, was characterized by consuming about 70% of invertebrates food until the fish are about 50 mm in length to less than 10% of the same when they reaches 250 mm31. This so called detritivorous is labeled as a notorious diet switcher, varying all the way from algae-detritus diet to a carnivorous one32,33. Study was conducted on a novel approach to prey recognition and feeding behavior, in wild Goliath grouper (Epinephelus itajara) in the field consuming both mobile and non-mobile prey on an artificial reef in the Gulf of Mexico34. The DNA barcoding as a method for piscine prey identification of three catfish species (one native and two invasive) of Chesapeake Bay, USA was also worked out35. Study that integrates fatty acid and isotopic analysis to understand foraging ecology of Chinook salmon in the California Current and demonstrates the value of combining these analyses for resolving foraging ecology was also being worked out these days36. Study on Pacific cod (Gadus macrocephalus) diet data as a basis for estimating octopus complex natural mortality and minimum biomass was also a new arena of study these days37. Studies were also conducted on a meta-analysis of the diets of 18 commercially-important ground fishes and their life stages from the U.S. Pacific Coast38. The present study was focused on identifying its feed composition of H. kurali and thereby identifying its feeding trend. This study forms the stepping stone as the feed so identified could be cultured under controlled condition, which will definitely open a new door to the field of aquaculture. By understanding the feed composition in the gut of fingerlings also puts light to the scope for larval rearing and thereby aquaculture promotion.
CONCLUSION
Study on food and feeding of Hypselobarbus kurali revealed the fact that the food preference of the fish right from its juvenile stage is for Daphnia sp. The knowledge on the feed preference had opened a new window to enhance the culture of the same under captivity. The live feed culture of Daphnia sp. will serve as food for the captively breed and reared new larvae of H. kurali. Thus this study forms a foundation for uplifting a new species on to the aquaculture scenario.
SIGNIFICANCE STATEMENT
This study discovers the feeding profile of the fish which is planned to be reared under captivity. Thus knowing the feeding priority will definitely help the researchers to develop the feed under controlled condition and to raise the larvae of the fishes providing their staple diet. This study will help the researcher to uncover the most crucial part of captive breeding which is the feed. Thus, this study helps to understand the feed requirement of a species which is planning to be breed under captivity.
ACKNOWLEDGMENT
The authors are grateful to the Western Ghat Cell, Department of Planning and economic affairs for their support.